Single cold radiator

After mother in law complaining the house was cold, we've tracked it down to a radiator that isn't warming up. Its a 5 foot double radiator, quite old model, downstairs on a combi boiler system.

I've tried bleeding air, but just get water, so air isn't the problem.

Looking at it from left to right, there is a TRV on the left hand side

- this moves freely, currently set at max.

On right hand side there is another valve - is this the lockshield valve? Again, this turns freely, and is currently (after messing around with it to see if that was the problem) is turned to max on. The "pin" inside this moves up and down freely, so is lower when it is "off" and higher when it is "on". When I turn it up and down, a small amount of water leaks from this valve, which I'm interpreting as "bad sign".

The feeding pipe on the right gets warm to the touch when the heating is on, the one on the left does not.

Any DIY options I could try here? Rad is in a room with a wooden floor, so not overly concerned about some leaked fluid, but wouldn't want a whole radiator contents to pour over the floor!

Would the whole system need draining down to take off just one rad? Presumably if one of the valves did need replacing, that would necessitate a complete drain down?

Thanks!

Matt

Reply to
larkim
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Take the head off the TRV and check the pin is not stuck down. (it should push in under firm thumb pressure, and spring back up when you release it). If it is stuck this will leave the water shut off regardless of the valves demands.

Sometimes they can be freed with a few taps on the side with a hammer, or the pin pulled up with a pair of pliers.

Sounds like stuck valve.

To remove the rad - not if the valves are working. However to replace a valve without draining is harder (especially if its a downstairs one!)

Reply to
John Rumm

If it is a stuck TRV then would this not be shown by closing the lockshield valve off and opening the bleed valve. It no water comes out then the TRV is stuck.

Adam

Reply to
ARWadsworth

In message , larkim writes

This has been covered recently. Take the top off the TRV and jiggle the pin.

Yes. IANAPlumber!

regards

Reply to
Tim Lamb

That reminds me of a task to empty a system. I couldn't find a drain c*ck anywhere so had no choice but to remove a valve and gain access as it was a lowest point in the system. I used a piece of hosepipe in conjunction with a short length of copper pipe and a compression coupler.

I undid the compression nut until the valve would free if I let go. All the time keeping pressure on the valve to ensure the olive still gave a good seal. I then very quickly removed the valve and quickly covered the end of the pipe with my thumb. After ensuring th threads were the same quickly put this coupler with hosepipe where the valve was and tightened the compresion nut.

I was surprised how little water I lost, and how slowly the inertia of water built up when my thumb wasn't on the end of the pipe!

With the house outlet a couple of feet below the house, and by syphon action I completely drained the system.

One thing I will say with to the OP. In the past I have discovered systems which didn't function as expected, and have found crossed pipes which were acting as if they were in a one-pipe system but where all the other radiators being connected to a flow and return pair. Worth bearing in mind.

Reply to
Fredxx

If the rad valves are both working, a single cold rad can be caused by the circuit being 'unbalanced' ie, the other rads are 'stealing' all the flow. If you reduce the flow through some of the other rads by partially closing their lockshield valves, hot water will now pass through the cold rad.

David

Reply to
David J

"On right hand side there is another valve - is this the lockshield valve? Again, this turns freely, and is currently (after messing around with it to see if that was the problem) is turned to max on. The "pin" inside this moves up and down freely, so is lower when it is "off" and higher when it is "on". When I turn it up and down, a small amount of water leaks from this valve, which I'm interpreting as "bad sign".

Not sure what is meant by a 'pin' on the lockshield

Reply to
John

I took it to mean that the spindle moved up and down on its thread, when rotated. The leaking water would be from the gland - which needs to be re-packed.

Reply to
Roger Mills

Don't bee too sure. You will struggle to bleed a system while the pump is running.

I can't answer that, cos I have no experience of TRV's

Dave

Reply to
Dave

SNIP

For lots of fun it is possible (with experience) to have a replacement valve ready, enclose the whole thing in a stout polythene bag and a seriously decent cotton soak sheet. With both hands inside the bag working VERY quickly you hold the old valve in place, remove the nuts, whip the old valve out of the way and have the new one in place before more than a cupfull of water is lost. Takes practice, confidence and even more confidence, but it does avoid draining down and creating all sorts of airlocks afterwards. Do make sure before you try this that the threads on the old and the new valves are identical. Some faint hearts plug the outlet and the vent at the feed and expansion tank before doing this. A kit called a plumbers mate consisting of two tapered rubber plugs is available for such a task

Reply to
cynic

No! Don't do that, shut the other non lockshield valves off on all other rads, then all the available flow goes through the cold rad. My system is like that, even though it is fed from a normal boiler. My system is a pig to get up and running again after a drain down because of all the loops in it and this is what I do to get it up and running again.

Dave

Reply to
Dave

Yup that would work. (as long as the lockshield shuts right off anyway)

Reply to
John Rumm

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TRV pin moves freely up and down, so it isn't that simple. Am I right in thinking that the hot should come through the locksheild as it does, or is my system the "wrong way round"?

Thanks for all the help so far!

Matt

Reply to
larkim

larkim presented the following explanation :

The answer to that, will depend upon the actual model of TRV. Some can be fitted in flow or return.

Reply to
Harry Bloomfield

How freely? It should take a reasonable push to move it down, and when you let go it should spring back up. If it's not doing that, it might be the valve is stuck, but the pin is not attached to it - so you can lift in independently.

Well both ends are connected to hot pipes, so some may conduct - more so if you bleed the rad when the heating is on. Even if the wrong way round it should still work. Some valves not designed for bi-directional flow (and even some that are) may hiss or whistle when on low flow with the direction wrong.

Reply to
John Rumm

OK, but I can conclude that the radiator itself isn't full of air (which I know is the first thought for a cold radiator).

Matt

Reply to
larkim

simply close off both valves, unscrew the rad and try flushing this out in the garden? Obviously there will be water in the radiator which I can deal with.

Matt

Reply to
larkim

Explained this to a mate once, when he needed to introduce a service valve and a tee into an existing set of rad tails. Vented system, not too much head etc. He said he understood what to do. Anyway, I was working on something elsewhere in his house and heard a "scream", went back to find a new valve assembly in place, but black iron stained water all him, and all over the place including the ceiling! I said I would do the next one. Pipe cutter until almost through - wiggle of the tail to snap it off and thumb in over the pipe end - then quick swap for the waiting valve - push down with one hand while doing up the compression nut a bit to quench most of the flow, before giving it is final tighten. Total water lost; about a cup full.

While watching me he commented that I had pre-assembled the compression joint first! (he had uncovered and recovered the pipe to place first the backnut, then the olive, and then the valve over the pipe, and also forgot to turn the valve off first!

Well worth having, but a carrot can work if you don't have those!

Reply to
John Rumm

Before doing that, have you done what someone else suggested - namely closing the lockshield valve and *then* opening the bleed screw? If little or no water comes out, it indicates that the TRV isn't opening even if the pin is moving!

If you *do* decide to remove the radiator, think carefully about how you're going to drain it. Your remark "Obviously there will be water in the radiator which I can deal with" suggests that you may not have thought about it enough! Assuming that you have a significant other of the opposite gender, getting black gunge from a radiator all over the carpet is *not* something I would want to do, just before Christmas!

Reply to
Roger Mills

Using the face of a hammer (pushing, not hitting!), the I can depress the pin about 3-4mm and it then returns quickly back to the start position. In fact, this is the same action as I've seen on other TRVs in the house that I know are working.

They are Siemens TRVs. Others in the house seem to be on the outflow side of the rad having walked around a few last night, so I think they are in the "right" place.

I'm now slightly concerned that there may be something more fundamental wrong - of the 6 downstairs radiators, in addition to the one I've flagged here, there is another 1 rad which is showing the same symptoms as the first - i.e. cold no matter what the TRV is set at. I haven't yet tested the TRV operation on this other rad as it was difficult to get to last night.

Both of the "dodgy" rads are on the front wall of the house, one in each room either side of the hallway. The hallway rad works fine, but I think that may be fed from the upstairs (its an oldish house), where as the pipes for both of these two rads come from under the floorboards. Both have hot inflow pipes (on lockshield side), but have no heat in the rads themselves.

The system was drained down and powerflushed about 12 months ago with fresh inhibitor added.

Could there be a blockage (air?) in the return loop just affecting a couple of rads? If so, how could I diagnose / fault trace? Is my logic wrong? How could just two rads be affected, not all of them. There are no zones in the system, as far as I am aware there is only one "zone", and the fact that some rads are working whilst 2 aren't leads me to believe it is a proper "trunk and branch" design rather than a single loop of pipework.

Thanks to one and all so far for all of your help / advice / contributions!

Matt

Reply to
larkim

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