TRV Problem?

[Camila]

I had my boiler serviced this week and at the same time I asked the engineer to fix a thermostatic radiator valve on one of my radiators. It had previously not been fixed properly meaning that the radiator was always on the highest setting which wasn't a big problem for me. However, now that the valve functions properly in terms of being able to turn it etc I have a problem with the radiator staying hot.
When I first put the heating on the radiator gets hot - but after an hour or so it's stone cold even if I adjust the TRV or the main thermostat temperature. I've tried it with other radiators in the house on and off but still get the same issue. I can only get that radiator hot again by turning off the heating, waiting for everything else to cool down and than turning it back on again.
Is this just a dodgy TRV? It seems that maybe the pin gets jammed in when the radiator is hot enough but isn't getting released again to get more hot water until the whole system cools down. That's my inexpert thoughts but would be good to hear if anybody knows what is likely to be the problem.

 

[Armo74]

A TRV works by measuring the room temperature, some are filled with wax, some with a liquid. The way it works is that you set the TRV to a certain setting and as the temperature in the room increases the wax/liquid expands pushing the pin down which closes the valve which stops the flow of water through that particular radiator. Then as the room decreases in temperature the wax/liquid retracts opening the valve letting the heated water flow through to heat the room again. I would suggest that it is doing it's job perfectly fine.

 

[Camila]

I've spoken to my plumber and he thinks there is a problem with the wax/ liquid that's stopping it heating back up once it's reached the temperature - even after the temperature goes back down again. It is not allowing the temperature to increase again until the whole system is stone cold. It should work by getting warm, shutting off when it is warm enough, and then as things cool below the required temperature to boost it up again. It isn't doing this - will only heat up again once the entire system has been shut down and restarted later once everything is cold.
So I'll try a replacement TRV.

 

[Armo74]

Remove the head and see if the pin pushes up and down, if it does try another head off another valve and see if that works if it does then it is a faulty head.