central heating radiator thermostat valve

[alan1947]

is it possible to replace the thermostat on the valve without replacing the complete unit.

[ianmunt]

Provided the plumbed in part is OK the top adjustable sectionis removeable and a replacement can be sustituted

[New Judge]

Beware if you have "Drayton" Thermostatic Radiator Valves (TRVs). (These are white with a solid chrome top).

The Mk3 and Mk4 valves look identical at a glance. However, the top parts of the two are not compatible. The threaded retaining ring which holds the top to the plumbed in part are of different sizes and so you cannot replace a Mk3 top with a Mk4 one. Mk4 valves are the only ones now available, having replaced the Mk3 (from memory) about 7 or 8 years ago.

All of my radiators originally had Drayton TRVs. I have to say they do not seem very robust. The usual fault is for the mechanism to fail so that the radiator is fully on at all times. Previously replacement was a simple matter of buying a new one and just replacing the top (5 minute job). Now I have to drain down the system, remove the entire valve from the radiator and plumbing and instal a new one (about one to two hours). As a result any that fail in the winter months have to wait until the Spring to be replaced as I do not drain my system in winter unless absolutely necessary.

Even some of my Mk4 Drayton valves (no more than 5 or 6 years old) have failed and I am now replacing them with "Salus" brand instead.