Air Lock/Blocked Cold Feed Boiling Issues - HELP!

[cr0ft]

Hi all,

Advice appreciated. I drained down a 13 rad open vented heating system today to replace all the TRVs on the ground floor. Obvious signs of corrosion in the system (header tank full of brown water).

Changed TRVs, on trying to fill the system realised that no water was coming in from the header tank (couldn't bleed any radiators at all). So I am thinking blocked cold feed.

After a bit of pipework alteration in the loft, connected the mains connection to the F/E ballvalve to the open vent pipe and carefully filled the system with mains pressure water down the open vent pipe, stopping to bleed all radiators. Eventually managed to fill all radiators.

Turned on the boiler and pump (having also set the 2 control valves to manual and bleeding the hot water indirect circuit) and the radiators are all getting hot, great news.

After about 10 minutes, boiling water starts spilling over into the F/E tank from the open vent (spurting out every 20 seconds or so).

Is this likely to be due to the blocked cold feed (which I'm looking to fix tomorrow) or is there something else afoot?

The boiler is about 15 years old and is an old floor-standing boiler. Grunfos pump which seems to be filled with water rather than air.

Any thoughts appreciated!

 

[Puddle]

Well get up and running correctly and see how you go,the blocked cold feed should not cause the problem,maybe restricted flow due to air in pipework or you could have damaged boiler thermostat if boiler run with air in heat exchanger/no water
If cold feed blocked up,possible blockage on flow from heat exchanger but if all rads getting hot hopefully not,persume cold feed going down to boiler,were it joins will probably be blocked point
Also possible check of pump and pump valve inners,to check clear

 

[stevetheplumber]

id say yes blocked feed probaly in the tee where it joins ive had similar some where pump over and not running right probably been doing it for ages and it seem when you drain it it gets worse

 

[cr0ft]

Should have been more specific, cold feed goes to airing cupboard on first floor, boiler is on ground floor. Arrangement on return pipe (in order of flow) is open vent, cold feed then pump. I'm guessing this arrangement could cause pumping over with a blocked cold feed. Going to get a magnet on the pipe today to check it - definitely know that the cold feed is heavily blocked, just not sure if it's what's causing the pumping over.

 

[fireblade]

Ijust put a gallo gun on the cold feed in the tank and blast it with co2 unblocked loads of fe tanks like this takes 5 mins if its not blocked it will just blow out the open vent

 

[fuzzy]

Should have been more specific, cold feed goes to airing cupboard on first floor, boiler is on ground floor. Arrangement on return pipe (in order of flow) is open vent, cold feed then pump. I'm guessing this arrangement could cause pumping over with a blocked cold feed. Going to get a magnet on the pipe today to check it - definitely know that the cold feed is heavily blocked, just not sure if it's what's causing the pumping over.

I have come across the cold feed being blocked on the tee as i enters the system on umerous occassions. i found something that expained why this happened but i cannot remember now. cut out the tee and replace.

this could and would cause pump over as it is the cold feed that allows expansion and not the vent. the vent is the safety valve and therefoe doing its job

 

[cr0ft]

Thanks for the info fuzzy. Feel a bit silly not knowing that it's the cold feed that allows the expansion, I thought it expanded through the open vent - oops!

Cut out the cold feed and replaced it today. Was then able to bleed all the radiators. Turned on the heating once the system was filled and bled, the pump was knackered 🙁

One new pump later, the heating system fires up and all works fine for 20 mins or so. Radiators heating up, new trvs working, very happy customer. Then the dreaded kettling starts again, followed very quickly by more water flying out of the open vent and me switching off the boiler and pump again.

My options as I see them now are: -

1. Put in some sludge remover, leave for a week, run pump without boiler to circulate sludge remover. How effective is sludge remover in a cold system?

2. Powerflush the system, hoping that this removes enough sludge and rubbish to get it all working again.

Found out today that the heating system is 27 years old and last had the inhibitor changed 12 years ago. Would have been nice to know that prior to starting the work - will make sure I ask next time!!

 

[Mackattak]

I have come across the cold feed being blocked on the tee as i enters the system on umerous occassions. i found something that expained why this happened but i cannot remember now. cut out the tee and replace.

Its something to do with the hot and cold water mixing at the neutral point over time. Also any blockages around these areas will create positive and negative pressures causing the pump to draw in air or pump over into the header tank respectively.

 

[fuzzy]

Thanks for the info fuzzy. Feel a bit silly not knowing that it's the cold feed that allows the expansion, I thought it expanded through the open vent - oops!

Cut out the cold feed and replaced it today. Was then able to bleed all the radiators. Turned on the heating once the system was filled and bled, the pump was knackered 🙁

One new pump later, the heating system fires up and all works fine for 20 mins or so. Radiators heating up, new trvs working, very happy customer. Then the dreaded kettling starts again, followed very quickly by more water flying out of the open vent and me switching off the boiler and pump again.

My options as I see them now are: -

1. Put in some sludge remover, leave for a week, run pump without boiler to circulate sludge remover. How effective is sludge remover in a cold system?

2. Powerflush the system, hoping that this removes enough sludge and rubbish to get it all working again.

Found out today that the heating system is 27 years old and last had the inhibitor changed 12 years ago. Would have been nice to know that prior to starting the work - will make sure I ask next time!!

The water is failing to get round then, its not returning for some reason? May require a flush out of some kind. Can you check the water temperature at the bottom of the rads, just before it pumps over. Also try taking all trv heads off and opening the lock shields fully and then run system. The TRV's can be over sensitive depending on type, may require 'slacking off'? try those things and please let me know what happens

 

[sparky]

Sludge remover best used at normal operating temperature. You say run with just the pump on is this because of the boiler/open vent problem?
How can you run the pump without the boiler? Turn the gas off?

 

[moogwai]

Ijust put a gallo gun on the cold feed in the tank and blast it with co2 unblocked loads of fe tanks like this takes 5 mins if its not blocked it will just blow out the open vent

what's this gallo gun?? not heard of one of them before!!! you say it will shift a solid blockage in the neutral point?

 

[stevetheplumber]

what's this gallo gun?? not heard of one of them before!!! you say it will shift a solid blockage in the neutral point?

i assume thats a pump up drain unblocker good tip moogie
not sure if an air seperator wouldnt split the state some of those get in

 

[moogwai]

i assume thats a pump up drain unblocker good tip moogie
not sure if an air seperator wouldnt split the state some of those get in

hmmm....never thought about using anything like that,wouldve thought it'll just push the blockage somewhere else in the system at some point and then you're back to square 1. think i'll stick to cutting the pipe out..at least i know the blockage has gone.
have you used anything like that stp??

 

[Billy Bob Bob]

Hi all,

Advice appreciated. I drained down a 13 rad open vented heating system today to replace all the TRVs on the ground floor. Obvious signs of corrosion in the system (header tank full of brown water).

Changed TRVs, on trying to fill the system realised that no water was coming in from the header tank (couldn't bleed any radiators at all). So I am thinking blocked cold feed.

After a bit of pipework alteration in the loft, connected the mains connection to the F/E ballvalve to the open vent pipe and carefully filled the system with mains pressure water down the open vent pipe, stopping to bleed all radiators. Eventually managed to fill all radiators.

Turned on the boiler and pump (having also set the 2 control valves to manual and bleeding the hot water indirect circuit) and the radiators are all getting hot, great news.

After about 10 minutes, boiling water starts spilling over into the F/E tank from the open vent (spurting out every 20 seconds or so).

Is this likely to be due to the blocked cold feed (which I'm looking to fix tomorrow) or is there something else afoot?

The boiler is about 15 years old and is an old floor-standing boiler. Grunfos pump which seems to be filled with water rather than air.

Any thoughts appreciated!

you probably have a blocked neutral point[were the cold feed enters the system]cut it out and replace

 

[fireblade]

Gallo gun is compressed co2 like air rifle cartridge would not leave home without one bought at parts centre i have cleared blockages in radiators and header tanks last one was after changing a cylinder heating would not fill gave the f and e tank a quick blast happy days got a handy cone one the end to put into rad air vents well recomended can also blow out dust etc heres a link just for info like i say bought at parts centre probably breaks up blockage like a drain unblocker does
Gallo Condensate Blowout Gun - AZ Partsmaster

 

[moogwai]

Gallo gun is compressed co2 like air rifle cartridge would not leave home without one bought at parts centre i have cleared blockages in radiators and header tanks last one was after changing a cylinder heating would not fill gave the f and e tank a quick blast happy days got a handy cone one the end to put into rad air vents well recomended can also blow out dust etc heres a link just for info like i say bought at parts centre probably breaks up blockage like a drain unblocker does
Gallo Condensate Blowout Gun - AZ Partsmaster

very interesting.....may have to invest in one just out of curiosity,good find fireblade.🙂

 

[fireblade]

Honesly moogwai excellent investment cartidges are not that cheap probably cheaper from an air rifle shop got to look into it i used to do the rads on the top floor of an office every winter they would not work used to try and vent them take the air vent out no water and no air used the gallo gun opened the flow on the first rad and the return on the last rad two or three blasts would clear it put the air vent in job done went to parts centre lad said do you want to buy one of these i said what would i do with that went back a month later bought one and never looked back no fun when you get a blocked cold feed late at night

 

[moogwai]

heh heh....just got one of fleabay with 6 cartridges for £30.....i look forward to using it on my next blocked cold feed,think ive got one in a few days.
so i just stick the attachment onto the cold feed inside the f&e tank and let it go??

 

[fireblade]

Yes mate water in the tanks a bit cold on the arm in winter just press on hard or it can get messy😀

Very satisfying when the water starts gurgerling down the cold feed good price off flea bay

 

[moogwai]

😀

Yes mate water in the tanks a bit cold on the arm in winter just press on hard or it can get messy😀

i know mate,will invest in some rubber gloves that go upto me elbows!!! i hate cold water!!! and i suppose the effect would be like a massive fart in a small bath!!!

there was only one on there so i thought i'd better grab it quick!

 

[fireblade]

very well described😀😀

 

[moogwai]

indeed....lol....will let you know how i get on with it.

 

[fireblade]

Cheers mate

 

[cr0ft]

Fuzzy,

Definitely not the TRV heads, I've replaced 7 and all are set to setting 5 (max) - new Comap heads and valves, that's how all this trouble started 🙂

There didn't seem to be any huge difference between the temperatures across the rads before it pumped over, not that I'm keen to turn it on again till I've found the fault - there was a LOT of boiling water flying into the tank.

Sparky,

It's an old floor standing boiler, when the boiler is off if I switch CH or HW on the timer, the relevant 2-way motorised valve opens and on comes the system pump (Grundfos). Water then begins circulating, including through the boiler (I can here it moving round). I don't want to turn the boiler on and leave it for a week or there will be nothing left of her upstairs ceiling or heating system probably!! Today was the first time I've been scared as a plumber, her central heating system was sounding like a steam engine!

Going to powerflush the system early next week, will see how I get on - I'm taking heart that it did actually run for 20 minutes today before problems started!

 

[fireblade]

wouldn't be the trvs shutting down with no bypass thats causing it to pump over

 

[cr0ft]

I thought of that too fireblade, but the upstairs towel rail doesn't have a TRV on it, so I guess that is the bypass. 🙁

 

[macplumb]

Have you opened the manual air vents ( if there is any) could be locked in the coil restricting flow so water is boiling off and blowing out of vent. Is the boiler triping out?

 

[Puddle]

sure we are not talking boiler thermostat gone and system over heating,boiling over?

 

[cr0ft]

Circulation around the system does seem to be there but it seems to be minimal even with the pump on setting 3. I do think the boiler thermostat is not working though, given how violent the overpumping/steam is into the header tank.

As she is an OAP, she's keen not to replace her heating system basically - the system is totally caked up with rubbish so I'm thinking a powerflush will do it no harm to try and get it working again. Perhaps this block-up has just revealed that the boiler thermostat is knackered too.

 

[fuzzy]

Circulation around the system does seem to be there but it seems to be minimal even with the pump on setting 3. I do think the boiler thermostat is not working though, given how violent the overpumping/steam is into the header tank.

As she is an OAP, she's keen not to replace her heating system basically - the system is totally caked up with rubbish so I'm thinking a powerflush will do it no harm to try and get it working again. Perhaps this block-up has just revealed that the boiler thermostat is knackered too.

i have had a problem with new TRV;s even when on 5 they shut down when the room is still cold? ive had to back off the nut holding the head. Just thought it may be something else to eliminate. id turn the pump down, if it is only going through 1 rad and set on 3 presuming the trvs are the prob it would pump over

did you check the bottom of the rads? how old are they? you could take 1 off and flush it through outside, check the amount of corrosion that comes out, thats a good indicator of the sludge that is in the system. Is the bathroom rad fully open?
Also, try running a hose pipe out of a lower drain with the system off but water keep filling it up, turn any motorised valves on and of, that should get rid of any air

 

[justlead1]

Hi Cold feeds are prone to corrosion as they are the nearest point to active water on cistern feed closed system. The movment of water due to expansion/contraction and evaporation can cause corrosion on beta brass fitting, valve etc. and is far more apparent on larger systems where iron barrel is used. Good Luck

 

[cr0ft]

Bathroom rad is very warm when system runs. Upstairs TRVs haven't been replaced (6 rads out of 13) and those TRVs were working ok before hence why I don't think TRVs is the issue tbh. I know for sure there is plenty of corrosion in the system, top and bottom - water in loft tank was brown with about 1 inch of sludge in the bottom of the tank. On closer inspection there is a sign of a pinhole leakage from one of the radiators.

I've resigned myself to powerflushing the system and have already told the customer that if it doesn't work then imo the system is at the end of it's working life.

Will see how the powerflush goes!

 

[fuzzy]

Bathroom rad is very warm when system runs. Upstairs TRVs haven't been replaced (6 rads out of 13) and those TRVs were working ok before hence why I don't think TRVs is the issue tbh. I know for sure there is plenty of corrosion in the system, top and bottom - water in loft tank was brown with about 1 inch of sludge in the bottom of the tank. On closer inspection there is a sign of a pinhole leakage from one of the radiators.

I've resigned myself to powerflushing the system and have already told the customer that if it doesn't work then imo the system is at the end of it's working life.

Will see how the powerflush goes!

i see, well with all youve said it appears to be sludge corrosion issue for sure, good luck

 

[cr0ft]

Thanks to all for their help with this. I powerflushed the system and cleaned the F/E tank out today and all is now working a treat, for now at least! A 27 year old system now seems to be working as good as new.

It amazed me that it worked for so long with so much rust and silt in it! The muck that came out of the powerflusher drain hose was incredible.

 

[fuzzy]

Thanks to all for their help with this. I powerflushed the system and cleaned the F/E tank out today and all is now working a treat, for now at least! A 27 year old system now seems to be working as good as new.

It amazed me that it worked for so long with so much rust and silt in it! The muck that came out of the powerflusher drain hose was incredible.

well done good result. It shows you it has been corroding for along time! all the rust comes from somewhere! Did you put treatment in?

 

[cr0ft]

Sure did. Risked an acid de-scaler clean too which seems to have sorted out the kettling in the boiler without exposing any unwanted leaks. 2 bottles of my local merchant's finest inhibitor in. Got the follow on sales, basically told her she needs to stop using whoever is servicing her heating and get me in to do it now 🙂 Luckily, I think she agrees..

 

[moogwai]

Sure did. Risked an acid de-scaler clean too which seems to have sorted out the kettling in the boiler without exposing any unwanted leaks. 2 bottles of my local merchant's finest inhibitor in. Got the follow on sales, basically told her she needs to stop using whoever is servicing her heating and get me in to do it now 🙂 Luckily, I think she agrees..

good stuff croft glad you got it sorted, there aren't many plumbers out there that wouldve done everything you have...most probably they would of said "not my problem"
you are like me...won't stop until i get it goin...in the long run you can only benefit from jobs like this one...word will get round.🙂