Trv Problems

[sddsddean]

Can the plastic thermostat bit of a TRV go wrong? One of our rads is not warming up. If I take the top plastic bit off, the pin in the top of the valve is free and the thus the rad comes on, so I don't think there is a problem with the valve itself. So it must be the thermostat bit, though I've never heard of one of these breaking and I can't find any info online, so do they go wrong? which means you have to buy a new one?

[Buenchico]

You seem to have answered your own question! If the pin is moving freely (and the radiator heats up when it's raised) then whatever controls its movement is clearly at fault.

You don't need to replace the whole valve though as you can buy the heads separately. e.g. http://www.heatingcontrolsonline.co.uk/radiator-valves-c-28.html/replacement-trv-heads-c-28_51.html

[KARL]

There is often a way to adjust the range across which the head activates the valve - the head contains a module which expands with rising temperature. What I think you might be able to do is shunt the range to cause the head to push the pin down later as the temperature rises. All this depends on the make and model of valve.

Another option to buying the head on its own is to buy an entire valve on eBay, even a used one, because this may turn out to be the cheapest choice, and then if the valve is discontinued then eBay may be your only option.

[sddsddean]

I really just wanted to see if the 'body' does go wrong, but tend to agree with you both that that is what has happened. I'll try swapping 2 bodies over this weekend and see if the other rad doesn't work, then I know if its the body or not. Thanks for your help.