Water discharging from the loft vent pipe as CH turns off?

[Markw996]

Hi,
I have just moved into my first home, a 2 bed semi-detatched and as the title says I have a very noisy central heating system.

As it comes on I get lots of bubbling / gurgling noises that last about 10 seconds and seem to originate from either the upstairs radiators or the airing cupboard.

Also as the central heating clicks off it sounds like someone emptying a bucket of water up in the loft right above my bedroom (very worrying the first time it happened!).
I traced the loft noise to the expansion tank in the loft where, as the heating clicks off, I am getting about half a litre of water discharging from the vent pipe back into the tank.

The system is open vented circa 1992 and I take the vent pipe to be the one that rises about a foot above the tank, then bends in a U shape back down into the tank.

I've had breif discussions with a plumber friend and he says it could be the boiler thermostat?!? but I suspect it is more likely to be air in the system somewhere (although I am certainly not clued up on central heating systems) as I did have to bleed a lot of air from by bathroom radiator when I first moved into the house due to it being very cold at the top.

Just to summarise:
I have 2 tanks in my loft and the problem is relating to the smaller tank which does the central heating.
My boiler is located in a downstairs cupboard.
My airing cupboard is upstairs and contains an immersion tank, pump, and a motorised valve of some sort.

I hope someone can help as the noises wake me up in the mornings and annoy the hell out of me in the evenings! 😱(

Many Thanks,
Mark.

 

[jase158]

Hi, When does it happen? (after heating has been on for an hour,as soon as heating comes on, when hot water in use i.e.)
Where do you live?

 

[kimbo]

Like all these jobs it is beter if you are there to make a good judgement however I would be thinking possibly pumping over the vent possibly pump set too fast, air being dragged in through the vent. The vent and cold fill in wrong place should be 150mm apart etc. More information would be good

 

[WHPES]

Easiest way to fix - convert to sealed system. The hours spent on determining the problem which may not be easily fixable would best be put to converting it over.

Do not leave it. Every time you draw air in will encourage rapid corrosion of the radiators, or lose water through the overflow will dilute any rust inhibitor.

 

[wards]

blockage in circs,find blockage in system and rectify,or call in a professional to carry out the work for you.

 

[stevetheplumber]

if its only a small amount of water each time it shuts of raising the vent or oversizing a section around the water line can stop this
but id try running pump down one notch first

 

[yorkieplumber]

Check pipework is correct in cylinder cuboard ie cold feed and vent, the fitting of a airjec is usually a good solution, converting system into a sealed system is rather a drastic measure.

 

[SafeGasInstall]

I might be wrong but I thing you need to get a auto bypass fitted ,if the fault is just after heating goes of ,but if it happens when working let say 1h then I think is the cold feed might be blocked

 

[Markw996]

Thanks for all the suggestions.

I have just taken some photos of the pipework inside my airing cupboard in case anyone can see anything wrong? (sorry but I don't know how to rotate them)



I've also turned the pump down to minimum (it was set on about 2 of 4) and I'll see if it gets better or worse.

The easiest solution seems to raise the vent pipe a bit higher, I may give that a go this weekend as it's a pretty simple job.

Thanks,
Mark.

 

[tamz]

Could do with a bypass valve or even a 15mm gate valve fitted. (on 15mm pipe 1st tee below pump). It is not really needed.
Turning the pump down should help. Also drop the water level in the F&E tank a bit by bending the arm of the ballcock down.

 

[Markw996]

Could do with a bypass valve or even a 15mm gate valve fitted. (on 15mm pipe 1st tee below pump). It is not really needed.
Turning the pump down should help. Also drop the water level in the F&E tank a bit by bending the arm of the ballcock down.

Thanks tamz, so I'll raise the vent pipe by about 10" and drop the water level in the tank by bending the arm and see if the problem goes away.

The vent and cold fill in wrong place should be 150mm apart etc. More information would be good

How would I tell which is the cold fill? Are you refering to the pipes in the loft? If so can you explain what I should be checking?

Unfortunately I don't have any more information at the moment, it does seem worse first thing in the morning though, maybe for the first hour of operation... and less so last thing at night if that helps? I'll have to monitor it for a few days to see if I can give better detail.

Thanks,
Mark

 

[tamz]

It is probably more pump related than anything else.
The system looks piped ok. Vent and feed max 150mm apart so it looks fine. Keep the pump on the lowest setting that it works on (simplified that one a bit).

Could be a bit sludge related.
What colour is the water if you bleed a rad?

 

[Plumbcrazy56]

I have rotated the pictures for you.

And as already stated, I would look for a blockage in the cold feed at the tee indicated by the X

 

[Markw996]

Could be a bit sludge related.
What colour is the water if you bleed a rad?

It was definitely quieter this morning with the pump on the lowest setting, it didn't even wake me up! 🙂

As for the rads, all give clear water except the one in my bedroom which is BLACK water 🙁

I have rotated the pictures for you

Thanks, it was starting to strain my neck!

Could I check for a blockage by removing the pump & rodding the vertical pipe? Or would I need to cut out the tee and replace it anyway?

Thanks,
Mark

 

[Plumbcrazy56]

Try draining the system without turning off the water to the expansion tank. if it drains but the tank stays full then you definately have a blockage.

 

[Markw996]

Check pipework is correct in cylinder cuboard ie cold feed and vent, the fitting of a airjec is usually a good solution.

Would someone be able to see from my photos if retrofitting an Aerjec to my existing pipework is a simple operation?
I know the cold feed is the vertical pipe directly above the pump, but which ones are the vent, flow inlet, and flow outlet?

Thanks,
Mark

 

[yorkieplumber]

Markw966 if you dont know which the vent pipe is and boiler flow, you need to call a proffesional in because if you alter the pipework and block the vent/expansion you could have some serious issuses, without been on site it is sometimes difficult to give a diagnosses, the fitting of a aerjec made by myson (i think) is a simple job to fit, but you need to be reasonable compatent, hope this helps.

 

[jase158]

Come on guys!!!!!!!!
This is not piped up right. The primary return should be connected to the cold feed and the Primary flow should only be connected to the vent, not the cold feed. It looks to me like you are pumping water from the tank through the system, which is circulating through the system. once you are switching it off then the excess water is going back up to the tank.
To test this go into the loft after heating has been off for a while and get somebody to turn heating on. If water in f & e tank goes down then you have a problem with the pipe work and positioning. This water does not go down very often. A few mm is fine but if it half empties then you definetly have a problem with pipe work.
Personnaly i honestly think you need to get a plumber out, this is a complicated system that seems top have had some DIY done before and will need looking at properly, it wont cost hundreds of pounds and you may even get an easy solution.

 

[Reg Man]

Come on guys!!!!!!!!
This is not piped up right. The primary return should be connected to the cold feed and the Primary flow should only be connected to the vent, not the cold feed. It looks to me like you are pumping water from the tank through the system, which is circulating through the system. once you are switching it off then the excess water is going back up to the tank.
To test this go into the loft after heating has been off for a while and get somebody to turn heating on. If water in f & e tank goes down then you have a problem with the pipe work and positioning. This water does not go down very often. A few mm is fine but if it half empties then you definetly have a problem with pipe work.
Personnaly i honestly think you need to get a plumber out, this is a complicated system that seems top have had some DIY done before and will need looking at properly, it wont cost hundreds of pounds and you may even get an easy solution.

Sorry but what century of heating have you come from. I would agree with you back in the gravity one pipe system days of the 1950's. Technology has moved on and the concept shown here is a now relatively out of date fully pumped system and is absolutely correct. (other than the cold feed may be blocked).

The concept is worked by locating the open vent a cold feed as close together as possible (within 150mm) on the flow pipe before the pump. The reason it has to be before the pump, is that this area will be the place of the least pressure on the system therefore preventing circulation into the header cistern.

 

[yorkieplumber]

sorry mate seen hundreds done this way, never had a problem, but i used to fit a aerjec instead of the pipework arrangment as pictured in earlier post, its called a Y plan system hence 3 port valve.

 

[yorkieplumber]

Reg Man thinks you and i think same way, am suprised by the lack of knowledge on this plumbing forum, to be quite honest am shocked.

 

[yorkieplumber]

In the old days when i was a wee lad systems were mainly gravity primaries in 28mm, and pumped heating circuit, 28mm flow from boiler went to cylinder flow on coil then you put a tee in a number 26 and the 22mm end carried on as the vent over expansion tank, the cold feed was on the return side of the cylinder coil. I think this is the system you refering to jase158.

 

[marinegmillie]

F&e vent pipe needs to be 450mm above cisten then back down in to cisten. Could join feed and vent with air separator.

 

[yorkieplumber]

Agree with marinegmillie, aerjec (air separator)

 

[Markw996]

Markw966 if you dont know which the vent pipe is and boiler flow, you need to call a proffesional in because if you alter the pipework and block the vent/expansion you could have some serious issuses, without been on site it is sometimes difficult to give a diagnosses, the fitting of a aerjec made by myson (i think) is a simple job to fit, but you need to be reasonable compatent, hope this helps.

Hi, I appreciate your comments.

This is my first house and my first ever look at a central heating system. I am learning fast and have bought 2 books and a DVD so that I can educate myself as to how it all works. To put you in the picture, I am competant with soldering and replumbed my parents new kitchen with ease.

I'm sure I will work out the best way to fit an aerjec given time to read the books (very in-depth) but I was just asking how I determine which is the boiler flow, and which is the return? They are marked on the boiler of course, but they travel around the house a bit before reaching the airing cupboard (where the mass of pipework is still a little alien to me).

Thanks to all the usefull posts, I like to know how things work so I can keep on top of things before they go wrong i.e. I never would have let the expansion tank get so scaled up as the previous owner has, I'll be checking that every few months!

For now, am I getting warmer? 😕



Thanks,
Mark.

 

[marinegmillie]

Cold feed and vent go up a foot with ya arrows, spot on.

 

[jase158]

This is what everything is?
To everyone who say i am wronge, this is the way i got taught Last year.
So obviously you have all done it and maybe there are hundreds of them out there but that doesnt mean it is right?

 

[marinegmillie]

Spot on jase158!

 

[yorkieplumber]

Agree spot on!

 

[yorkieplumber]

but in a earlier post jase, you said it was wrong, am confused now.

 

[Reg Man]

Jase158, I take it that we can now disregard your post number 18, and we will go with your post number 22.

 

[marinegmillie]

I think what he ment is where the cold feed and vent is piped to pump, the cold feed is quite direct into pump, maybe pulling in some water hence venting back over to get rid, just a thought.

 

[jase158]

but in a earlier post jase, you said it was wrong, am confused now.

I was saying the arrowed pipe is wrong as it is pumping water through the return? the opposite way that you want it? I have never seen one of these installed like this?
And secondly I have never seen a fully pumped system this way? I have learnt something and it proves that college is absolutely useless, all my diagrams in my books show the vent and cold feed going into the boiler, but the pump should be after the vent and cold feed. Surely there must be another way as this looks to me like it will draw water from the F and E tank.

 

[jase158]

I think what he ment is where the cold feed and vent is piped to pump, the cold feed is quite direct into pump, maybe pulling in some water hence venting back over to get rid, just a thought.

finally somebody who understands, is there no other way that this can be piped up?
And for all those who say that this is ancient plumbing, my plumbing doesnt even have a pump. So pumped central heating only cant be that ancient.

 

[Reg Man]

Jase158, I thinking about sliting my wrist over this thread. There are alot of forum members who have an enormous amount of experience probably some go back to 1960's. The H lay out as it is known has been around since the introduction of fully pumped central heating systems back in the 1970's. It is the only proven method of installation which works and does not cause pumping over on an open system Ect: Give me any manufacturer boiler instructions from this time to current day and it will show this method of piping. Your labeling on the photograph is spot on.

 

[jase158]

Jase158, I thinking about sliting my wrist over this thread.

Thats a bit drastic? I was saying that i was wronge and everyone else is right,

May i just explain a couple things,
1. I have never installed a pump or a full central heating system
2. I am relatively new to plumbing, compared to some of the people on here,
But what i am saying is, just because everybody does it this way and it works this way doesn't neccessarily mean its right, although it is right this time
and isn't there any other way of doing it?

 

[jase158]

Let me just ask a question.
Where the pump connects in does it pull water as well as push the water around the system? or does it simply push the water round?
If it pushes only then obviously this is where i am getting confused, but if it pulls the water, what prevents it from pulling the water from the F and E?

 

[Reg Man]

Thanks jase158, feel better now.

The best leap forward I think, is sealed systems. They don't suffer many of the water quality problems you get on the open systems. Only draw back is the manual top up.

 

[jase158]

Thanks jase158, feel better now.

The best leap forward I think, is sealed systems. They don't suffer many of the water quality problems you get on the open systems. Only draw back is the manual top up.

Doesnt this have to be a new (ish) boiler though, Condensing type or combi? as there has to be a AAV, Expansion Vessel and PRV?

 

[Reg Man]

From post 19 Quote:The concept is worked by locating the open vent a cold feed as close together as possible (within 150mm) on the flow pipe before the pump. The reason it has to be before the pump, is that this area will be the place of the least pressure on the system therefore preventing circulation into the header cistern. Quote:

 

[Reg Man]

Doesnt this have to be a new (ish) boiler though, Condensing type or combi? as there has to be a AAV, Expansion Vessel and PRV?

Not necessarily. I fitted sealed systems back in the 1980's on cast iron boilers. They did have to be fitted with overheat thermostats and manufacturer would have to state it was suitable for sealed systems. The expansion vessel, PRV, Pressure gauge and filling loop were the extra bits we had to install.

 

[RoryD]

You have a blockage, you will need a powerflush and perhaps a reconfiguration (clearly haven't seen the system). I get this all the time mate.

 

[Markw996]

You have a blockage, you will need a powerflush and perhaps a reconfiguration (clearly haven't seen the system). I get this all the time mate.

Thanks, I have a plumber coming to powerflush the system tomorrow afternoon, in preparation of me fitting all new TRVs and a Magnaclean.

I might ask him to fit an air separator at a later date as I can't get my head around the flow & return connections.

 

[tamz]

Jase158, I thinking about sliting my wrist over this thread

😀😀

May i just explain a couple things,
1. I have never installed a pump or a full central heating system
2. I am relatively new to plumbing, compared to some of the people on here,
But what i am saying is, just because everybody does it this way and it works this way doesn't neccessarily mean its right, although it is right this time
and isn't there any other way of doing it?

Still got a lot of learning to do eh🙂

Let me just ask a question.
Where the pump connects in does it pull water as well as push the water around the system? or does it simply push the water round?
If it pushes only then obviously this is where i am getting confused, but if it pulls the water, what prevents it from pulling the water from the F and E?

If i have time later i will draw you a couple of pictures that will help explain how it works.

 

[philip mc geown]

i agree have been in many an old house with this type of layout, but it is a reconised piping method and many people still use it 2day!

 

[fuzzy]

cannot see how that system works, isnt the return joing on the positive side of the flow, how does the water get round?

 

[fuzzy]

oh its a bi pass i presume, will adding a bi pass valve help?

 

[tamz]

oh its a bi pass i presume, will adding a bi pass valve help?

It is a bypass without a valve. Fitted by an eejit as it is not necessary in the first place and if he fits one, at least valve it.

If the kids don't come through i'll not be doing much tomorrow so i may explain how different systems work with a few drawings.

Clue = neutral point.

 

[efficient]

got to be the best post ive read.... ****ing myself here about you lot arguing over a basic layout. The layout is spot on other than the bypass needs a ABV on it. If there is water coming out the vent pipe then theres got to be a blockage not allowing the circulation hence water coming out the vent its got nowhere else to go..

 

[Reg Man]

got to be the best post ive read.... ****ing myself here about you lot arguing over a basic layout. The layout is spot on other than the bypass needs a ABV on it. If there is water coming out the vent pipe then theres got to be a blockage not allowing the circulation hence water coming out the vent its got nowhere else to go..

Totaly agree. Its basic layout, the only way to pipe up open systems over the years. I think some of the forum posts, got a little consfused.

 

[fuzzy]

It is a bypass without a valve. Fitted by an eejit as it is not necessary in the first place and if he fits one, at least valve it.

If the kids don't come through i'll not be doing much tomorrow so i may explain how different systems work with a few drawings.

Clue = neutral point.

yes tamz it is due to the neutral point, obviously punping over is under positive pressure ie, pushing not pulling, did they suss out the problem? is the pump on the right way? if it was working properly then started to fault there must be a reason. if its been like that from new or since some work was carried out then all fingers point to that!

 

[fuzzy]

just read some posts, yes i agree the layout is VIP and therefore as good as it gets, cold feed is the neutral point and therefore the vent is within the neutral zone and shouldnt pump over all else being correctr. ive seen loads of these blocked at the cold feed.

When waters hot it should expand up the cold feed, if it blocks it wont be able to expand into the F&E cistern and has to expand up the vent. then it cannot come back into the system. its not really pumping over as such but expanding over. saying its pumping over leads people to believe theres a feed and vent fault, without seeing the system in operation its hard to say but i agree cut out the tee and replace would be first check.

fuzz

 

[Bartdude]

What's going on?? What's this ancient system? They don't show this on the course.

I'll tell you what,let's rip it out and stick a combi in😛

 

[tamz]

The basic principles of system design are being lost due to combi's and sealed systems being more popular bit it should be important to know the basics.
There are dozens of ways to pipe a system all based on a few basic layouts.
Understanding how the position of the feed vent and pump effects the water circulation helps.
Here are a couple of drawings. (this could have been a far longer post but i have simplified a lot of things)

I'll start with this one. Basic common layout for a gravity HW, pumped heating on an old cast iron boiler.



The position of the feed connection to the system is called the neutral point. Everything from the pump to the feed is under positive pressure (from the pump) and everything after the feed is negative.
In this drawing the only part of the system under positive pressure is from the pump to the boiler (as this is effectively the point the feed connects). The rest of the circuit is under negative pressure (the water is being pulled).
Because the cast iron boiler holds so much water it also acts as a neutraliser and the water flow from the pumped side slows right down so has very little effect on the gravity side.
It used to be though having the pump on the return like above would help the gravity circuit. In reality it didn't have any real effect.
A system laid out like this will not draw air or pump over (unless a blockage is introduced).


Same system with the pump on the flow. The heating circuit is now under positive pressure (being pushed). This is the better pump position as pumps can push better than they pull.

Move on a few years and motorised valves are introduced and systems become fully pumped. Still using high water content cast boilers, so we get something like this.

Feed and expansion still connected to boiler so position of the pump does not cause it to pump over or draw air. Pump on the flow so the system is under positive pressure.


Same thing with pump on the return. System under negative pressure.


If you use a low water content boiler or the feed and expansion are taken from the pipework, where or how they are connected starts creating problems.

Pipe it as above and a suction effect is introduced to the expansion pipe and if the pump is set too high it will draw air. Fitted like this to a low water content boiler where the pump speed usually had to be set high this is why a lot of systems fitted in the 80's/90's are full of sludge.
Easy quick way to over come this was to combine the feed with the expansion like this

This stopped the problem as the pump had to pull water from the F&E tank rather than air. It was not ideal though.

So they developed this system

Provided the feed and expansion tees were kept within 150mm of each other, the pump would have very little effect on the expansion pipe. Go much beyond the 150mm spacing and it will pump over.

There are dozens of variations of these layouts. Just think how the position of the feed and expansion will effect the system or introduce blockages and think what would happen.

A bit quickly explained and i have missed out a lot but the basic principals are shown. Hope this is of some use to someone.

 

[tamz]

What's going on?? What's this ancient system? They don't show this on the course.

I'll tell you what,let's rip it out and stick a combi in😛

They don't show much on the courses because they probably don't fkn know. Combi is the answer to everything😀

 

[fuzzy]

yuve too much time on yer hands tamz!!! lol
youve pretty much said what i said but with more background, i agree alot of newbies tend to favour combis as its all they know. i dont think its the tutors who are at fault, lazy and/or semi skilled plumbers are

 

[tamz]

yuve too much time on yer hands tamz!!! lol

I know lol

 

[SafeGasInstall]

" i dont think its the tutors who are at fault, lazy and/or semi skilled plumbers are"

don't think you were born skilled .....every one deserves a chance and every one who wants to become pro will go through anything to become pro !!!

Thank you for your time TOM !!!!

 

[Horse]

Gents,
New to this so please be gentle.

I have tonight noticed a small amount of warm water spurting out of the vent / overflow pipe into the FE tank when the pump turns off, in water or heating position. Not a lot less than half an egg cup. Only noticed when overflow started dripping outside.
Looking at the vent pipe outlet which was under water its been there a while. (Blue colour)
I have just recently removed and refilled a radiator during decorating. About a week ago.
I have some brown sediment in the tank but whole system is only 10 years old.
I have read the thread and the position of the neutral pipework looks about right.
What height should the overflow/vent pipe invert be above the water level in the tank?
Mines about 4-5 inches. I have seen 18 inches quoted elsewhere but the boiler installation manual says nothing.
When the pump runs I can see a gentle wafting backwards and forwards of sediment around the FE tank outlet.

Any help/advice/sympathy would be gratefully received.
Horse

 

[SafeGasInstall]

dear horse,
first you need some one to see it or picture would help . you have corrosion starting in your system (luck of having inhibitor) ! have you had any air in your radiators lately any cold spots ?

 

[apple-plumbing]

If the Vent pipe is discharging back into the F&E Tank but the water level doesn't rise high enough to reach the Warning Pipe and discharge outside then the Cold Feed from the F&E to the Hot Water Cylinder won't be blocked. The water level in the F&E should be 1/3 full when cold to allow for expansion when everything gets hot. The level should however be above the Cold Feed. The arm of the Ball Valve can be bent down to achieve this. The Cold Feed and Vent Pipe should be as close together behind the CH Pump to encourage Negative Pressure. The boiler could be boiling the water and the Vent doing it's job. The Boiler has a thermostat which can fail and could be checked by a plumber to see if this is funtioning correctly. The Vent Pipe should rise at least 450mm above the F&E and back down in a big arc, to prevent any surge effects - hope this helps

 

[Horse]

dear horse,
first you need some one to see it or picture would help . you have corrosion starting in your system (luck of having inhibitor) ! have you had any air in your radiators lately any cold spots ?

Thanks for the response. I will get some pictures and post. I have no cold spots and the recently removed radiator only had a little black sludge in it. I have had a little air 'single wooshing' in the system recently, twice I have heard it, in the last month. I fitted an auto bleed valve on the radiator in the bathroom (did it as it was a new tall ladder type radiator, over a year ago) I have not had a problem with air in any radiators since. I would add at present the vent pipe outlet is below the overflow level, so when I noticed it today the pipe was 1 inch under water. Have checked the thermostat and it is operating fine. Also it does this in CH a only as well as Hot Water. Again thanks. Horse

 

[apple-plumbing]

If you turn everything off and leave to cool, drain a bucket of water from the CH system via a Drain Valve on the Ground Floor with a Hose, does the level in the F&E drop? This will test for a blockage where the Cold Feed tees into the circuit and the only way expanded water can escape is through the Vent Pipe...this is quite common

 

[Reltub]

Looks from them pics like it's piped up correctly few things i would look at ; Pump the right way round, is there enough head above the pump(2m), flow and returns the right way round.

 

[Horse]

Hi
Thanks for reply the tank did overflow. Well dripped so blocked feed a possibility. As soon as I can( work commitments) I will try your drain refill test and get back. I will change the vent pipe height and arc as well. Thanks for staying with me on this. I will post as soon as I can.
Horse.

 

[tamz]

Raise the vent to around 450 above the F&E and take it out of the water. Bend the ballcock down a bit to reduce the fill level and bail some water from the tank.

 

[SafeGasInstall]

and get some local plumber to power flush you heating and put inhibitor before is to late

 

[Markw996]

Hi,

The plumber let me down on Friday but should be coming Thursday to powerflush my system.
Whilst it's drained I'm going to do a few modifications to the pipework to try to rectify the problems I've been having.

I've finally worked out how to best fit an Aerjec to my system, I'm also going to replace all my leaky or old TRV's, and extend my vent pipe a little bit.

The ballcock has been bent down a bit and I've bailed out about 15 litres from my F&E tank (Feed & Expansion 😕 ).

Finally, could someone please give me a BES part number of a good quality bypass valve to fit into my vertical 15mm bypass pipe?

Thanks,
Mark.

 

[fuzzy]

Easiest way to fix - convert to sealed system. The hours spent on determining the problem which may not be easily fixable would best be put to converting it over.

Do not leave it. Every time you draw air in will encourage rapid corrosion of the radiators, or lose water through the overflow will dilute any rust inhibitor.

shouldnt be hard to find, think converting is an expensive cop out

 

[fuzzy]

Hi,

The plumber let me down on Friday but should be coming Thursday to powerflush my system.
Whilst it's drained I'm going to do a few modifications to the pipework to try to rectify the problems I've been having.

I've finally worked out how to best fit an Aerjec to my system, I'm also going to replace all my leaky or old TRV's, and extend my vent pipe a little bit.

The ballcock has been bent down a bit and I've bailed out about 15 litres from my F&E tank (Feed & Expansion 😕 ).

Finally, could someone please give me a BES part number of a good quality bypass valve to fit into my vertical 15mm bypass pipe?

Thanks,
Mark.

its a common componentglad your sorting the problem, blocked feed is most probable
just ask at your local plumbing merchant for an auto bi pass,

 

[Bartdude]

I'd use the Honeywell bypass valve on this page.

By-pass, Pressure Reducing Valves & Thermostats<br>Condensate Pump & Fittings

 

[SafeGasInstall]

If it was me i would def change valves before power flush ,but let the plumber do the job other way you might flad the house, and it will be you ho will pay for it !

 

[Reltub]

I wouldn't use an airjec I find the "H" system alot better, also rather than a power flush if the sytem is really badly sludged i would recommend a manual flush i.e taking all the rads off the walls and manually flush outside with a hosepipe, this method is alot better than powerflushing in my opinion and can be quicker and gurantees a clean system, i would then also add some sludge remover to help clear the pipework and give a couple of flushes. Would also repipe the cold feed in 22mm.

 

[fuzzy]

i dont like airjecks, i dont like pumps pointing down either, they recon its fine with an h or airjeck but boisey in my experience

 

[apple-plumbing]

If the conclusion after the 'drain test' is the Cold Feed is not blocked and water is not entering the F&E via a faulty Float Valve (isolate the Float Valve for a few days to test for this), then you may have a breech in the HWSC. The design in 'vented' systems where the CWSC's water level is higher than the F&E means that there need only be a pin hole in the Cylinder's coil for the difference in head pressure between the 2 circuits to force water to backfill into the Primary Circuit causing the F&E level to rise and overflow. The only place these 2 systems mix is in the Cylinder and it's common for an old Cylinder to breech and present you with these symptoms

 

[SafeGasInstall]

good point apple -plumbing but this will be continues overflowing in the f&e ,not just a high level of water

 

[Horse]

good point apple -plumbing but this will be continues overflowing in the f&e ,not just a high level of water

Thanks for the input. The fill is only a 'spurt' when the pump stops, in CH or Hot Water, not a continuous flow. I wondered if it been like it a long time, and has only shown due to the tank ballvalve refilling after the radiator was put back, slightly raising the level to near the overflow. But I will do the tests above and report back as soon as I can. Cheers

 

[SafeGasInstall]

and put some pictures here to make it easy for all of us

 

[Horse]

and put some pictures here to make it easy for all of us

Will do

 

[tamz]

The fill is only a 'spurt' when the pump stops, in CH or Hot Water, not a continuous flow.

It is caused by a bounce in system pressure as the pump stops. It will be cured if you lift the vent higher.

 

[jase158]

The basic principles of system design are being lost due to combi's and sealed systems being more popular bit it should be important to know the basics.
There are dozens of ways to pipe a system all based on a few basic layouts.
Understanding how the position of the feed vent and pump effects the water circulation helps.
Here are a couple of drawings. (this could have been a far longer post but i have simplified a lot of things)

I'll start with this one. Basic common layout for a gravity HW, pumped heating on an old cast iron boiler.

View attachment 2125

The position of the feed connection to the system is called the neutral point. Everything from the pump to the feed is under positive pressure (from the pump) and everything after the feed is negative.
In this drawing the only part of the system under positive pressure is from the pump to the boiler (as this is effectively the point the feed connects). The rest of the circuit is under negative pressure (the water is being pulled).
Because the cast iron boiler holds so much water it also acts as a neutraliser and the water flow from the pumped side slows right down so has very little effect on the gravity side.
It used to be though having the pump on the return like above would help the gravity circuit. In reality it didn't have any real effect.
A system laid out like this will not draw air or pump over (unless a blockage is introduced).

View attachment 2126
Same system with the pump on the flow. The heating circuit is now under positive pressure (being pushed). This is the better pump position as pumps can push better than they pull.

Move on a few years and motorised valves are introduced and systems become fully pumped. Still using high water content cast boilers, so we get something like this.
View attachment 2127
Feed and expansion still connected to boiler so position of the pump does not cause it to pump over or draw air. Pump on the flow so the system is under positive pressure.

View attachment 2128
Same thing with pump on the return. System under negative pressure.


If you use a low water content boiler or the feed and expansion are taken from the pipework, where or how they are connected starts creating problems.
View attachment 2129
Pipe it as above and a suction effect is introduced to the expansion pipe and if the pump is set too high it will draw air. Fitted like this to a low water content boiler where the pump speed usually had to be set high this is why a lot of systems fitted in the 80's/90's are full of sludge.
Easy quick way to over come this was to combine the feed with the expansion like this
View attachment 2130
This stopped the problem as the pump had to pull water from the F&E tank rather than air. It was not ideal though.

So they developed this system
View attachment 2131
Provided the feed and expansion tees were kept within 150mm of each other, the pump would have very little effect on the expansion pipe. Go much beyond the 150mm spacing and it will pump over.

There are dozens of variations of these layouts. Just think how the position of the feed and expansion will effect the system or introduce blockages and think what would happen.

A bit quickly explained and i have missed out a lot but the basic principals are shown. Hope this is of some use to someone.

Wow thank you for this, I never got taught any of the other systems in college. The first system was the only one we got taught. I paid 600 pound at college and did not get shown any of that, the only part we did get taught was that pumps must be after the vent and cold feed. But nothing to that extent, thank you

 

[apple-plumbing]

In the early stages of a breech in the coil in the HWSC, the symptoms can worsen when the Primary Circuit is hot, as it can open allowing water to back fill from the Secondary Circuit. When the Primary cools down it could close. Combine this with a 4% drop in water level plus bailing the F&E, this may give the impression the overflow is not continuous. I agree, I would expect the Vent Pipe to vent due to a blockage when expanded water takes the shortest route to escape from the Primary Circuit. If there is a blockage in the Cold Feed this will prevent the water from re-entering the Primary Circuit trapping it in the F&E causing the level to rise every time the system vents until it overflows. But if the volume of water continues to rise intermittantly and the shortest route is the one open to atmosphere (as it has least resistance), this maybe the early signs of a breech too. Replacing the CF section of pipe as it joins the Flow would confirm if there was a blockage at this point. Partial blockages around the system can also cause these symptoms, Power Flush on Thursday and let us know the outcome

 

[tamz]

Wow thank you for this, I never got taught any of the other systems in college. The first system was the only one we got taught. I paid 600 pound at college and did not get shown any of that

Stick a pound in the charity box of your choice for the lesson😉

 

[apple-plumbing]

One final test for a coil breach inside the HWSC is to isolate the taps & toilets in the house and electricity to the boiler. Isolate the Float Valves to the CWSC & F&E too and mark the water levels on the inside of the tanks. If after a set period of time the water level in the CWSC has dropped and risen in the F&E there is a breach. The longer the period of testing, the more conclusive the results will be

To test for Pump Over, cut a 2 litre soft drink plastic bottle in half and securely & safely hang this from the top of the Vent Pipe using string (may have to insert a fitting to have something to hang off) so that the open end is under the end of the Vent Pipe where it would discharge into the F&E, to catch any water pumped over. It's important to test that should it fill the plastic container it will still overflow into the F&E. Ensure the plastic container is large enough to hold a fair amount of water without putting too much strain on the Vent Pipe. If it's full after a normal cycle of demands for HW and/or CH (and these can be tested for separately) there may be a blockage (or partial blockage) somewhere in the pipe work. This is normally where the Cold Feed from the F&E tees into the Primary Circuit. Cut out & replace. Pump Over normally introduces oxygenated water into the CH too, so more air than normal being collected in one of the Radiators and black when bled are signs of Pump Over

Pump Over can also be attributed to the CH Pump being installed the wrong way round and bad design; where the Vent Pipe & Cold Feed (in that order) are not connected correctly (normally within 150mm of each other) at the neutral part of the circuit

 

[Horse]

Sorry taking so long to post a response. I extended the vent pipe the extra amount as suggested to give a better arc. I also passed a small 6mm od tube down the outlet of the expansion tank all the way down and past the joint that we thought may be blocked. There were no discernible blockages. I bent the ballcock arm to roughly leave the tank 33% full. Everything now appears ok and when the pump stops I can see a little warm water (thermal blur) coming back up the Expansion tank outlet, like it should do, with nothing spurting out the vent pipe. Thanks to all the people who contributed advice, it was most appreciated and proved to be 100% correct.