GB wrote:


I took the actuator off, and there's a spring loaded piston on the
hydronic part which I can't move. I'm not sure how stiff this is
meant to be? This part of the system is all in 28mm pipework, so it's
a really chunky valve and I'm not clear how easy it ought to be to
move the piston?

In frustration, I gave the piston a few taps with a hammer. On the third
tap, it suddenly sprang upwards, and we now have central heating again! (As
it was stuck fully down, that explains why no amount of pushing would get it
to go down further.)

So, the next question is whether the valve needs replacing? A bit of WD40,
maybe? In short, what do I need to do to stop this repeating, please?

Thanks for all your help.