I posted a while ago about radiators heating up when the central heating is
turned off but just the hot water is turned on (conventional boiler).

I've realised that the radiators are also heating up - almost all of them -
when their thermostatic valve is switched off.

It seems too much of a coincidence that every thermostatic valve - about 8
of them - could be faulty.

Does this sound like a reverse circulation problem?

If so is there a way of fixing it without causing too much disturbance to
pipe work?