On 15 Feb 2021 13:10:00 GMT, David wrote:

On Mon, 15 Feb 2021 12:21:54 +0000, Caecilius wrote:

I've got about 18 radiators with Drayton TRV4 valves. I'm not sure how
old they are as I can't see any date stamps, but I suspect they're about
20 years old.

I'm finding that many of the TRVs shut off at a fairly low temperature
(around 20 degrees) despite being turned up to MAX. Removing the
sensor head completely solves the problem, so I suspect that some of the
sensor heads are starting to malfunction due to age.

Is this a known issue with old TRV4 sensor heads and should I plan on
just replacing the problematic heads, or does this behaviour often
indicate a problem with the valve itself like the spring becoming too
weak which means I should be considering replacing the valves in the
summer?

There should be an adjuster inside - little brass screw which can be wound
in and out.

If the screw can be wound in further then the maximum temperature may go
up.

I can't see any adjustment screw on mine - the only adjustments I can
see are the temperature setting on the main body of the head, and the
limit pin & holes on the underside. There doesn't appear to be any
non destructive way to dismantle the sensor head.