Cold radiator - help with diagonosis

[PeterL]

Converted the garage last March (into a bedroom) and extended the central heating system to provide a single radiator in it (off a combi boiler). Tested, and everything was fine. Finally put the central heating on this week ('cos it were fecking cold), and the rad in the new bedroom stays cold. The flow pipe gets hot right up to and including the valve, but the rad and return stays cold. This tends to suggest to me that the valve is faulty or blocked.

Can anyone give any pointers, please, before I strip the rad off the wall?

[Roger Mills]

What sort of valves are on the rad? Is one of them a TRV? If so, chances are that its pin is stuck down. You need to remove the thermostatic head (which doesn't involve any water leakage) and check that the pin can be pushed down and will spring back up when released. If it's stuck down, gently tap the side of the valve with a spanner to free it, or pull the pin up with a pair of pliers and then check that it moves properly. [Be very careful not to bend the pin or mangle it in any way - 'cos that will either stop it working or make it leak].

[Ericp]

Bleed the rad.

[Heliotrope Smith]

"PeterL" wrote in news: [e-mail]:

Air lock. The valve is not blocked or faulty.

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[PeterL]

"PeterL" wrote in news: [e-mail]:

Air lock. The valve is not blocked or faulty.

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I forgot to say that I have bled the rad; it is full. This is a bungalow. The flow and return is in the roof space with drops to individual or pairs of radiators. There are a pair of bleed valves on the main runs in the roof space, which also test good.

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[harry]

There may be air trapped in the pipework. The pipework should be installed so that any trapped air will move to a place where it can be bled out. You probably have a high point in the pipe where the problem is. You might be able to move the air along by shutting all radiators down except the one not working and running the pump at full speed.. But the problem will reappear at somepoint,

OR The system may need rebalancing. (ie lockshield valve adjusting.)

[tony sayer]

In article , Heliotrope Smith scribeth thus

Well I've had 4 stuck TRV valves, usually unstick themselves after a well placed wallop on the actuator pin and 0 airlocks..

Just remove the TRV body and see if the small pin sticking up is doing just that, if not genteel tap with small hammer and or if you can wiggle it with a pair of small pliers and it will usually free itself. This happens sometimes after a period of non use as is your case...

Also bleed the rad which you should do from time to time anyway..

[DerbyBorn]

tony sayer wrote in news: [e-mail]:

I guess TRVs are more liable to sieze if the control is left fully closed or fully open for a long periods as the pin won't be being moved.by the wax cartridge (Defeats the purpose of a TRV in my opinion)

[charles]

the control can be at a mid way point and the rad is shut off in summer becasue the room is warm enough. So it could stay in tegh shut position for three or four months - depending on how warm the summer is.

[David WE Roberts]

This suggests that if you turn the heating off for the summer you should remove the TRV so the pin is fully up. Default status next winter is the radiator works. Also normally easier to push down a stuck pin than pull one up.

Cheers

Dave R

[charles]

taht assumes you trust the "summer" to keep you warm. Since I use my gas boliert to provide hot water, the CH will come on as required. None of this "you can't have heating until November" that I remember from my schooldays

true, but it may then stay down. 'Stuck' tends to mean 'stuck' as I have found in the past.

[PeterL]

In article , Heliotrope Smith scribeth thus

Well I've had 4 stuck TRV valves, usually unstick themselves after a well placed wallop on the actuator pin and 0 airlocks..

Just remove the TRV body and see if the small pin sticking up is doing just that, if not genteel tap with small hammer and or if you can wiggle it with a pair of small pliers and it will usually free itself. This happens sometimes after a period of non use as is your case...

Also bleed the rad which you should do from time to time anyway..

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I wish it was as simple as a stuck pin, which unfortunately it isn't because it pushes down and bounces back quite freely. As harry suggested, I'm going to shut down all the other rads, put the boiler on max, and see it that does it. If it doesn't, then I'm going to strip the rad off and hope I find something!

[tony sayer]

In article , PeterL scribeth thus

Well....

Try this. Sure the other valve is opening?

Assuming both valves are closed. Then open the vent screw and see if water comes out. If so turn Both valves shut. Water flow should now stop.

Open One valve and if water then flows out that that valve is working OK, well passing water;!.

Then shut that valve and open 't other one. If water passes then that valve must be OK if not then its not passing anything. If your sure its pin is moving then it must be duff.

Least that way you can track down the faulty valve as if the "input" side is open and the flowing out is "closed" then water will still not flow.

Have fun;!...

[charles]

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another 'killer' is sludge. This can accumulate in low points. It can be quite messy to get out. I did this once in our village hall. It involved catching the sludge in a bucket under that rad feed pipe. Luckily the floor had quarry tiles.

[The Natural Philosopher]

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BTDTGTTS

shut off Every radiator expect the one that is cold and run the pump at maximum rabbit. That SHOULD blow any air out of the roof pipework and into the radiator where you can bleed it.

[thescullster]

If other suggestions don't work and you have to take the radiator off...

Turn off boiler etc and manually open any motorised valves.

Then with a bucket to catch the proceeds, open the feed and return radiator valves one at a time to see if you get decent flow.

I had a similar situation to yours where crud had blocked flow at the valve itself. Pipe got hot as far as the valve, but virtually no flow into rad. Had to carefully position a bucket and then open the valve and rod through it into the feed pipe with a plastic tie-wrap to release the crud.

Phil

[PeterL]

As suggested here, I shut down all the working rads by the TRV and ran the boiler at max setting. That did the trick. The non-working rad got hot quite quickly. Starting with the rad closest to the boiler, I then went back to all the working rads, shut down the lockshield valve, opened the TRV fully and gradually opened the lockshield until the rad got hot. I left the lockshield wide open on the two rads furthest from the boiler and found that the rads nearest to the boiler only needed one turn on the lockshield before they got roasting hot.

Thanks for all the helpful suggestions.

[DerbyBorn]

"PeterL" wrote in news:afdaboFh26vU1 @mid.individual.net:

Glad you fixed it - I was concerned that you thought you would somehow find a fault by removing the radiator! I think of balancing thus: If a pump can push 10 gallons a minute around a circuit and you have 10 radiators that can each pass 2 gallons a minute, then why would the water go to the most difficult radiator? Balancing ensures that all radiators get a share of what is being pumped around. I know that there is more to it than this - but it helps me to understand why balancing is needed.