On 29/01/2011 09:26, harry wrote:
On Jan 28, 10:54 pm, wrote:
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.

Give it a dose of ptfe spray and see what happens. If it jams up again
you can decide whether to keep freeing it or pay out for a new valve.
Finding the problem took the time.
BTW, you can hear if a pump is running by pressing a big screwdriver
tip to the pump and the handle to your ear.

"The pump impeller shaft is definitely turning, but I have no way of
knowing whether the impeller has come off the shaft. "

Andy