old thermostatic radiator valve

[petronius]

I am trying to replace the head of a very old thermostatic radiator valve (TRV), but it is difficult to find one with same thread size (I am talking about the thread of the securing ring that can be turned by hand and secures the valve head to the lockshield).

I showed the valve to a plumber who told me that the brand is West and that they have a smaller thread than most brands. He says that I should try independent merchants, but I had no joy after a few attempts.

Any help on where to find a compatible valve?

[jfgw]

I suggest a search for "Westherm" or "Comap Westherm". If all else fails, try eBay.

There are adapters available: https://www.heatingcontrolsonline.co.uk ... p-386.html

Julian F. G. W.

[jfgw]

It is best to replace like for like when replacing TRV actuators. Even if a different brand fits, the adjustment range is not likely to be correct and may be unusable. Designs do change and a new actuator may not correctly fit an old body even of the same brand.

I did make a comparison between some different brands seven years ago. Most of what I found will still be valid.

Valves checked were:
Danfoss;
Comap Westherm;
Screwfix;
Terrier;
Siemens;
Drayton;
Honeywell.

I have used the terms "keyed" and "not keyed" to identify where valve actuators are prevented from turning (or not) when attached to different bodies. I can only give a rough idea of how well a particular actuator will work on a particular body.

Danfoss uses a unique fitting and is not compatible with any other brand.

Comap Westherm uses a smaller screw thread and is not compatible with any other brand checked

A Screwfix actuator will not fit any other body. The screwfix body is very similar to the Terrier one but has a square key, not a hexagonal one. It appears to have been made in the same factory but is designed not to be compatible.

A Terrier actuator will not fit any other body.

A Siemens actuator will fit the following bodies: Screwfix (not keyed, likely to shut off at a low temperature even when set to maximum); Terrier (not keyed); Drayton (not keyed); Honeywell (good fit, likely to work fairly well).

A Drayton actuator is the best all-rounder. It will fit Screwfix (keyed but loose); Terrier (not keyed); Siemens (good fit, likely to work fairly well); Honeywell (good fit, likely to work fairly well).

A Honeywell actuator will not fit Screwfix, Terrier or Siemens bodies. It fits Drayton (not keyed).

Julian F. G. W.

[petronius]

Brilliant info - thanks jfgw!

For me the main question is, will a new Westherm valve head be compatible (in terms of thread and functionality) with the old body?