Are radiator valves (ambient) temperature sensitive?

[andycambo]

I've had a radiator off in a room for about two weeks whilst the room got plastered.

Today, I opened the windows a little more than usual to try and help get the remaining moisture out of the room so I can get painting this weekend. About an hour later I stick the heating on as it's pretty cold here at the moment and then a further 20 mins later noticed the boiler had dropped all of its pressure.

I tried to refil and the pressure dropped rapidly which is when I rapidly dropped one and run upstairs to see water gushing out of the point where the radiator connects (the one with the heat controls).

Basically nothing has been touched so can only assume the drop in temperature has cause the metal in the valve to contract and therefore no be completely sealed any more.

Could there be another reason it could completely fail? I've now closed the window and have a candle underneath to see if that will work...

[vdp1]

You need to take the thermostatic top of the valve and screw a plastic cap on instead. The valve will open if the temperature drops close to freezing in the room.

[andycambo]

vdp1 said:

You need to take the thermostatic top of the valve and screw a plastic cap on instead. The valve will open if the temperature drops close to freezing in the room.

Cheers, was hoping it would be something simple. Will go seek a plastic cap!

[vdp1]

Hope I'm not too late. Just to add, if you unscrew the thermostat of the top of the valve this will have the same effect of opening the valve fully so either put the rad back on or blank it off somehow.

[dirkgently]

Go to a plumbers merchant and buy some 1/2" or 3/4" brass caps depending on valve size. Never trust a valve to hold.

[Gingerbread Man]

You get 'decorators caps' for this exact reason that screw the TRV totally shut. Otherwise they will open up for frost to prevent freezing.

If you can't find the cap, you can buy a brass cap which can go over the radiator/ valve joint. Seal this with a rubber washer in the cap, or PTFE on the valve threads.