cold rad

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cold rad

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PaulRB

I have 1 cold rad in a downstairs cloakroom.
I have flushed it, tested the valves ( not trv ) and connected a hose from the o/side tap to each valve to blast any air-locks.
I have turned off all other rads and it still won't work.
I have replaced rad with a length of 15mm pipe and the pipe gets hot immediately! Put a new rad back on and it works for 2/3 days then fails.
If I draw 1/2 a bucket from the return pipe, hot water is drawn thru the flow pipe and the rad works for 2/3 days.
I know it could be a blockage, either air or sludge, but how come I can always draw hot water thru if I drain from the return pipe?
It seems as if there is something stopping the free flow thru the system which I can by-pass by encouraging the flow when draining.
I would be interested in advice as to what should be my next step.
Someone must have come across this before!!
Thanks
 
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PaulRB said:
ok rad has 2 pipes - 1 bringing hot water, other returning water to boiler. I think of them as the flow and return pipes.
There is a drain valve on the return pipe which I can use to drain about 2/3 pints.
This is replaced by hot water thru the flow pipe and, once I have some circulation, the rad will work for 2/3 days, until the water in the system cools. Then I have to drain again. ( obviously I can't keep draining so I'm looking into why the rad works for 2/3 days then stops )
I think you're right about the hot water by-passing the flow pipe but I can't get at the joint to put in a swept tee.
Not the pump - it's new + working fine.
Thanks
Click to expand...

you could be drawing air from the flow yes, and this may heat up the rad yes, but if theres an aitr lock on the return it wont work or will partially work. shut the flow valve and draw the water through, that will drag water from the return pipe

is the pump the same size and power? what setting is it on?
 
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Reply to Halesowen 1

Ok Ok I hear you!
Trouble is, I phoned around to get a plumber in.
Regular guy said he was just too busy, 3 others didn't even get back to me.
I've spoken to about a dozen plumbers down at the local plumbers merchants and they've all said the same thing ie; air lock, sludge, long pipe run, by-passing tee etc.
When I tell them what I've done they all scratch their heads and say they would've done the same.
If I could find 1 plumber who said " I know what that is. I've come across it before. Do this." I'd jump at it.
The only thing I want to avoid is taking up the carpet/floorboards in the other room to access the pipe joint.
However, that may be the only way.

Can you tell me why I can get hot water into the rad AND it will carry on working fine for 2/3 days before stopping.
If the new pump can circulate the water ok for 2/3 days why do you think its the pump?
Appreciate your help, thanks.
 
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well its certainly something causing it, im still not convinced you have all the air out of it, until you isolate the return and draw it from the flow pipe then do the same with the flow you will never be sure all the air is out

air can be trapped at the top of pipes but not the full bore, therefore restricting flow but not stopping it. if thi sis a long run when it fires from cold it may bi pass. you have to keep trying these things or you may never find out

once you have eliminated this check the pump power, the speed you have it on.

then if all this is fine and you say valves are fine and pipework fine you only have option of putting swept tee in and/or re pipe if you want a proper solution
 
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Thanks.
When I drain down the system to fit an air vent and iso valves I suppose I could also fit a drain valve in the flow pipe and try shutting off the return valve + drawing water thru the flow pipe.
I've tried running the pump on all 3 settings but no joy.
I really think it needs a swept tee but I didn't want the hassle of gaining access.
Might have to swallow it and take up the carpet.

Thanks again
 
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Why are you fitting iso valves and air vent??
All the system worked fine before with nonw of this. This will not solve your problem.
Have you balanced the system correctly once you have had heat to the rad??
Did you buy the identical pump??
Why would it need a swept tee?? it has never had one before.
Think logically, none of these things on system when it was working fine so why would you put one in now??
Where abouts are you?
 
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are the pipes level, bit of a long shot but if they have air in a bit of pipe which isnt straight, the air will stay there, with using for a few days steam (or something similar as wont be steam as has to be 100 degrees to get steam) could buid up and cause it to completely block, when draining slightly it is removing a little bit of air and then building up over a few days?

told you it was a long shot, but to find out if this is even remotely possible, check the pipes in loft to see if they are level. if not, try to lower them.
 
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have you altered the height of the peipes when you swapped the rad? that may have put a air lock situation in the pipes?

dont worry about aav's just draw the water from each pipe seperately, that will clear the air if there is any

if its dragging air in it will be poor vent inlet position or a leak on the negative side of the system
 
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Ok.
Fitting air vent in pipe in case it is an air lock.
To do this, I will have to drain the system so I might as well fit iso valves in 2 pipes feeding the rad so that, at a later date, if I can't solve the problem, I can fit a towel rad with heating element without having to drain the whole system.

Yes I bought the identical pump.
I'm in Dorset and around here plumbers are like gold-dust. It does P me off though, when they don't even return a call.
Haven't altered height of pipes. Already thought of that and I took up floorboard in wardrobe to access pipework in the hope that I could lower the pipework and reduce chance of air lock.
Not possible because pipes travel over 2 walls.
I will try dragging hot water into rad with all others turned off and leave the system like that for 3/4 days to seee if rad continues to work.
If it does, that would point to balancing of system.
If it stops working after 3/4 days I don't know what could be the cause.
I suppose I find it so frustrating because it does work properly for those 2/3 days.
Thanks
 
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If all else fails pressurise it, with a Expansion vessel , filling loop and Prv valve you can buy them as a kit. Not too expensive that would be my next move,bit of a strange one, .Good to hear all the idea's though.
 
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PaulRB said:
Ok.
Fitting air vent in pipe in case it is an air lock.
To do this, I will have to drain the system so I might as well fit iso valves in 2 pipes feeding the rad so that, at a later date, if I can't solve the problem, I can fit a towel rad with heating element without having to drain the whole system.

Yes I bought the identical pump.
I'm in Dorset and around here plumbers are like gold-dust. It does P me off though, when they don't even return a call.
Haven't altered height of pipes. Already thought of that and I took up floorboard in wardrobe to access pipework in the hope that I could lower the pipework and reduce chance of air lock.
Not possible because pipes travel over 2 walls.
I will try dragging hot water into rad with all others turned off and leave the system like that for 3/4 days to seee if rad continues to work.
If it does, that would point to balancing of system.
If it stops working after 3/4 days I don't know what could be the cause.
I suppose I find it so frustrating because it does work properly for those 2/3 days.
Thanks
Click to expand...

may work for 3/4 days if a partial air lock, thats why i asked if the pipes had moved, ive had it before, long shot i know but we are running out of options. dont put aav iin, its a waste of time, drawing water out of each pipe will solve air problem if it is. shut of both valevs and take off rad, connect hose to each outlet and drag through
 
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Thanks Fuzzy.
Haven't moved any pipes.
I'll have to fit a drain valve on the flow pipe in order to drag water thru.
Already have one on the return pipe.
Are you saying that, once I draw water thru both pipes, any air should be gone and the system should work as normal?
What worries me is that after working for 3/4 days air may be getting back into the system, or do you think I'm not actually purging the system of air and its the same air gradually returning to the pipe, causing a blockage?
Wouldn't an air vent cover that possibility?
When you talk about a poor vent inlet position, do you mean the pipe that hooks over the expansion tank in the roof?
If so, couldn't I extend that pipe to end underwater, so it couldn't suck in any air?
Thanks
 
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i cannot ensure you that it will fix the problem but it will eliminate the problem being air.

fitting a aav could cause issues, if air is entering the system theres a problem, if you try to fix this by aav you will keep bringing in fresh water which is untreated and has fresh oxygen, therefore it will cause corrosion, not a good idea. aavs are only there to help initial filling

dont extend the pipe, it shouldnt suck in air, were is the vent (hooked pipe) inlet, cold feed to sysem and pump in conjunction with each other?
 
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There is a vent pipe hooked over the expansion tank in the attic.
Directly below the expansion tank is the airing cupboard with a copper hot water tank, pump and 3-way valve.
The boiler is in the garage.
I think I need to shut the wheelhead valve on the flow side and then drain some water from the system, clearing it of air in the return pipe.
Then shut the lockshield valve on the return side and drain some water from the system, clearing it of air in the flow pipe.
Then I shouldn't have any air in those pipes.
You may be right that air is trapped in the return pipe which is stopping the circulation, and I thought it was in the flow pipe.
Thanks.
 
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Hey PaulRB....let me know how it goes. I am trailing you trying to work this out.
I eventually got my rad to warm up by turning all other rads off but it took a loonnnngggg time and it didnt even get hot....just warm to the touch!!
Put the rads back on and kitchen rad still does not work.
 
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whats the output of the new rad compared to the old rad?

im guessing that restriction in a towel rad is greater than normal rad which may restrict flow more than previous and contribute to it not/struggling to circulate
 
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Thing is, I've shut off all the other rads and I've shut off just the towel rad and it still hasn't helped.
The new rad is a direct replacement for the old one.
I know from talking to people that this is a very common problem. A rad stops working for no apparent reason, usually when you switch on the heating for the first tine after summer.
Thanks
 
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Can't really suggest anything that hasn't already been said other than fitting auto air vent is a bad idea. Yes if it is air it will work but when you move house it will be still there under the floor unseen and may cause a plumber agro!

Like the diy'er who tiled his bathroom floor over his c/h pump and a year later it needed replacing.

Nothing worse than working on a system thats been 'messed with'.

Get those carpets up Paul!
 
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Sorry, haven't had time yet. Still gotta work!
I hope to have a go on Thursday.
Realise I don't need to put a draincock on the flow pipe, I'll just turn off the valve at the rad. That way I know when I drain some water from the return pipe it must be replaced with water from the return pipe, and hopefully will flush out any air in the pipe.
I'll let you know how I get on.
Thanks
 
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some drain off valve combinations require the return valve to be open, it may be difficult for you to ensure flow from the flow pipe if this were to be the case
 
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Ok, but I plan to shut off the flow valve while I drain water from the system.
With that valve closed I know the water coming out must be from the return pipe ( can't come from the rad because there will be nothing to take its place ).
I hope that will force any air out of the return pipe ahead of the water.
If it works I will then re-open the flow valve knowing there must be no air in the pipes.
Then I'll see if the circulation returns to the rad.
I'm really hoping that, when I open the draincock, I will hear spluttering and know air is coming out!!
If I can clear all air out of these 2 pipes there should be no reason for the water not to circulate.
If it still doesn't work at least I know it can't be an air lock.
Gonna try this tomorrow.
Thanks again.
 
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PaulRB said:
Ok, but I plan to shut off the flow valve while I drain water from the system.
With that valve closed I know the water coming out must be from the return pipe ( can't come from the rad because there will be nothing to take its place ).
I hope that will force any air out of the return pipe ahead of the water.
If it works I will then re-open the flow valve knowing there must be no air in the pipes.
Then I'll see if the circulation returns to the rad.
I'm really hoping that, when I open the draincock, I will hear spluttering and know air is coming out!!
If I can clear all air out of these 2 pipes there should be no reason for the water not to circulate.
If it still doesn't work at least I know it can't be an air lock.
Gonna try this tomorrow.
Thanks again.
Click to expand...

mmmm, id be more confident if you did the same with the flow, your only pulling water from return, you really should do the same with the flow to ensure 100% you have no air
 
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let us know how it goes

remember you must do the same with both pipes to ensure there is no air in them. doing it with one valeve closed only ensure that pipe has not air in it

if you only do it with the return as you suggest it only ensure the air is out of that one, doesnt prove anything with the flow

after tyhis it may not be air but at least you can eliminate it once and for all
 
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Ok Guys, ( especially Fuzzy ), this is what I've done today, Saturday.
Tied up the ball-cock in the expansion tank so it doesn't fill with new untreated water.
Turned off both valves on problem rad. So any water I drain must come from return(-) pipe and not from rad or flow(+) pipe.
Opened draincock and drew off 1/2 bucket of water. Plenty of spluttering and flow stopped for 1/4 to 1/2 a second before continuing, so obviously a lot of air in return(-) pipe.Took bucket up into attic and refilled expansion tank.( level had not dropped below outlet pipe so no air being drawn into system )
Repeated process and this time water flowed as normal.( refilled expansion tank )
Opened both rad valves and drew off another 1/2 bucket in case there was air in the flow (+) pipe but water flowed nicely. ( refilled expansion tank )
Went round and turned off all other rads and put heating on.
5 mins later we had hot water coming thru pipes and rad got very hot. Turned all other rads back on and ran system for 1 hour. Everything ok.
However, I've had the rad working before so I won't know if this has solved the problem yet. I've turned the heating off and I'm gonna let it cool right down for 24 hours and then fire it up again.
Fingers crossed!!
At least I know there was air in the pipework, now I have to wait and see whether air is getting into the system, which is a different problem. I hope the air was trapped in the pipe when I refilled after replacing the pump and, now I've purged the system, it works as normal.
I'll let you know tomorrow.
Thanks guys.
 
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Ok.
So far so good.
Put the heating on this pm and hot water came thru straight away.
Still not 100% sure the problems solved. It'll take a few days of working before I can relax and put it out of my mind.
I still have to balance the system
Meanwhile I will keep you all posted as the week goes on.
If air isn't getting into the system I should be alright.
I know a lot of people have this problem and are following the thread so I think I should point out some of the main points because different systems and installations would require different solutions.
However, with all the help on hand here, I'm sure most problems can be solved.
I have a gravity fed, 2 pipe system with an expansion tank in the attic.
There is a cylinder in the airing cupboard together with a 3-port valve and pump.
The boiler is in the garage.
Downstairs our floors are concrete so all the downstairs rads are fed from above in a "loop" system.
All downstairs rads have draincocks on their pipework so that when you drain the system, you have to go round each rad and drain them individually if you want to completely drain the system.
I understand that the "loop" system is susceptible to air locks when filling up the system and that appears to be whats happened to me.
I've been lucky because I have draincocks on every rad but other people may not so the things I've tried may not work for everyone.
However, the amount of help and support provided by the guys on this forum should enable everybody to solve their problem.
I thank you all for taking the time and trouble to help out and sticking with it when nothing seemed to be working.
My wife thanks you all too!!!
Hopefully I will report that all is working fine in a weeks time.
Cheers
 
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