Hi all

My heating system has two Landis and Gyr 2-way spring-return motorised
valves (Landis and Gyr ZA-V222). The one for the hot water cylinder
gets stuck in the open position, so even if the mains power to the
system is turned off, the spring does not return the valve to the
closed position. It first did this on one occasion two weeks ago, but
since then has been working fine until yesterday. Now it sticks every
time. I removed the synchronous motor and found that I can manually
return the valve to the closed position by rotating the toothed plate
(which normally meshes with the cog on the synchronous motor) but it
needs a quite a lot of force. If I then use the spring-loaded "manual
override" lever to move the valve towards the open position, the
return spring does not have enough strength to pull the mechanism back
towards the closed position.

Are there any tricks to free up a jammed motorised valve, or do I need
to replace it?

thanks

Julian