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
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larkim wrote:

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!)
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John.

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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
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ARWadsworth wrote:

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

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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
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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.
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Regards,
Harry (M1BYT) (L)
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On Dec 7, 11:25pm, Harry Bloomfield

Presumably if I am happy that neither valve will "leak" water, I could 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
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In an earlier contribution to this discussion,

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!
--
Cheers,
Roger
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larkim wrote:

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.
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John.

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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
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In an earlier contribution to this discussion,

There could well be an air-lock somewhere. The first thing to try is to turn off all rads except a cold one, and run the system for a bit with the pump at its maximum speed. Any air should collect in the top of the rad, where it can be bled out. Repeat - one rad at a time - with any others which are not getting hot.
When you can get them all hot one at a time, turn them all on again and set the pump back to its normal speed. They should then all get hot at the same time. If some are hotter than others, the system will need balancing.
If there are any radiators which refuse to get hot even when everything is thrown at them, come back, and we'll make some more suggestions.
--
Cheers,
Roger
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OK, that sounds like useful practical advice. Will try tonight. Not sure I can set the pump speed any higher (its a WB greenstar, 24 I think) but I get the principle of forcing everything at one rad only and will have a look at the pump settings.
Cheers!
Matt
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larkim wrote:

ok, that sounds like it is doing what it should then...
You say this is a combi. Can you confirm if the system is vented or sealed? (i.e. header tank for vented, or filling loop and pressure gauge for a sealed system). (the former are prone to airlocks, but not usually the latter)
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John.

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Sealed (no header tank). Before the current boiler (c. 12 months ago) I used to get persistent issues with top rad in the house filling with air, I think from a small perforation in the pipework near the boiler. With current one I don't seem to have this problem, so I don't naturally think there is any air in the system, and I haven't heard any banging etc etc.
I suppose its possible that built up gunk from the old water in the system has been dislodged in the powerflushing and is now blocking the 2 radiators?
Matt
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"larkim" wrote
I suppose its possible that built up gunk from the old water in the system has been dislodged in the powerflushing and is now blocking the 2 radiators?
Matt
I had that! After forcing water flow towards the two blocked rads, the blockage moved to one rad only (the two rads were served by the same 15mm flow and return pipes). The crud actually blocked the valve itself, so had to remove the rad, open the valve and poke the blockage through the valve with a tie wrap! Once disturbed, water started to flow out of the vave, so put a hose on the valve to run water into a bowl and complete the de-blocking operation.
Phil
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It could be that the lockshield valve has dropped. The valve snaps off and then sits at the bottom of the valve blocking the flow. Of course opening and closing the valve would not show this fault as these limits are set by the threads in the valve.
Adam
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John Rumm wrote:

That reminds me of a task to empty a system. I couldn't find a drain cock 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.
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"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
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In an earlier contribution to this discussion,

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.
--
Cheers,
Roger
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In message

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

No.
Yes. IANAPlumber!
regards
--
Tim Lamb

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