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.