I have the exact same thing in my house. I have no less than 3 of these Drayton TRVs in exactly the same condition. 2 of them have been broken for a couple of years but are in rooms where I don't need to adjust the temperature.

Broken Drayton TRV4C head | PlumbersForums.net Broken Drayton TRV4C head | PlumbersForums.net

I also remembered I dislike them because the body only allows the pipe and 15mm tail to go into it a very short distance, which means no adjustment possible to suit pipes and not compatible with straight swaps with other brands bodies to original nuts and olives. In that video he talks about balancing, ensuring -11c from flow to return. Does anyone know how specifically 11c? Best thermostatic head on the market, replaced 6 defunct British Gas Heads that were awful and ugly, this is a classic design and has a lovely smooth action, Setting 3.5 is about 21 Deg and just work perfectly keeping the house warmThis Drayton TRV4 Head Classic is A rated for efficiency making it one of the most energy efficient thermostatic rad valves available. The Drayton TRV4 head is suitable for most domestic heating sytems, with superb temperature range and easy to use functionality. Featured in angled chrome, the valve is also able to balance the system via the TRV. A thermostatic radiator valve allows you to set a radiator at a different temperature, so you can heat your home only where required. This can help reduce your home's energy consumption. Is what it appears to be. Solid and appears genuine. Identical to my original radiator valves so easy replacement when an original one broke

Broken Drayton TRV4 Radiator Valve | PlumbersForums.net Broken Drayton TRV4 Radiator Valve | PlumbersForums.net

Look like Toolstation sell the head on its own. I have mine arriving today. If it works ok, I'll replace the other broken ones in my house.

If testing the trv in the warmer months,Running a trv on 3 or 4 will also delay its re opening and add on the expected delay response time of +/- 20 minutes. Beauty Advent calendars are significantly pricier than chocolate ones, but they've become increasingly popular in the last few years as a way of bagging beauty products at a fraction of the normal cost. They often sell out early, but can also be heavily discounted later if they don't, so here's a round-up of some of the best I’ve seen. If this happens, you may be able to loosen it up by tapping on the valve body multiple times. Tap very gently with something like the end of a screwdriver.