Thermostatic Radiator Valve (TRV) Faulty?

4 Aug 2006
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United Kingdom

At the weekend I replaced two radiators downstairs and while I had the system drained down decided to put a TRV on the bathroom red. Both other radiators upstairs already have them which I fitted a couple of years ago.

The problem I have is that the bathroom radiator does not get hot, its gets very slightly warm (but not much) even with the TRV fully open or the TRV head itself removed.

The pin in the TRV moves freely if I press on it, as well as returning to its original position (maybe 6 or 8mm in height). When the central heating is running the pipe and valve itself gets hot, but the radiator only very slightly warm, as though the TRV is partially blocked or faulty.

I then tried closing off both the TRV and the radiator valve on the other side and draining water from the radiator, the water drains until the level in the radiator drops and then stops. If I open the standard valve on the radiator, the water then begins to flow again. If I shut off the main valve and open the TRV (or take the head off) the water drips out of the bleed valve as though the TRV does open, but only very slightly.

The TRV is dual flow and reversible and I have used two of the same type in the past on other radiators no problem. Thinking about it, I probably replaced the lock shield valve with the TRV but with it showing the flow works either way that should not matter should it?

I thought maybe there was an air block so ran the central heating pump on full for a while with all the other radiators shut off, no change.

Is it just a case the valve is faulty?

Also if I get a new one could I risk just disconnecting the existing one and fitting a new one without draining down? (I stupidly put inhibitor in the system before I checked the radiator was working fully so don't really want to waste another £30 on 2 litres of Sentinel).

For reference the system is a Thermal store, with 10mm plastic pipe. All the other radiators are heating up perfectly.

Cheers for any advice,

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try turning off all other rads to expel air from pipework.
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Did you rebalance the system after replacing the downstairs rads? Also have you tried balancing the bathroom rad?

Thanks for the replies.

I have tried turning all the other rads off and just having the bathroom one on, no help at all.

I have also set the lock shields on the other rads to as they where before I messed with the system. It should be noted before the TRV in the bathroom the rad got very hot indeed with its standard valve on.

I'll have another mess about.

Hmm, I have just noticed if I shut ALL the rads off except the bathroom one, then neither pipe, nor valve gets warm or hot to the touch? Then if I let other rads open for a bit, then shut them down the TRV on the bathroom gets hot but rad doesn't.



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