Earlier this week I tried to turn the thermostat head on the lounge radiator to adjust the temperature to discover it had seized solid. I have used Drayton TRV4s for all of the thermostatic valves I have replaced so far. Anyhow, the reason the head had seized was because the gland seal around the actuator pin had started leaking - not passed the pin, but around the threads that secured it. Expecting to have to replace the whole valve (approx 10 years old), drain down etc., I had bought another valve and Fernox MB1. But after some absent minded Googling on the subject I discovered that this gland seal is replacable. So I rang Drayton and they directed me to a video on their web site (under installer how-tos) showing the procedure. The best bit was that the job could be done live (without draining) and Drayton sent a couple of seals and a plastic tool FOC!
Service worthy of note
Phil