V4073A CH won't shut off

[beniamino]

I have a V4073A with a worn out actuator (teeth worn down). Thanks to posts on this forum, I understand that although I can replace the actuator, the real problem is usually that the valve itself is stuck. However, I've removed the actuator, and manually turned the valve with a pair of pliers. It moves pretty easily throughout its whole travel, and seems like it switches OK between CH and HW (the correct pipes get warm). But if I leave it on HW only, after a few minutes the CH pipe is hot, and after 20 minutes, the radiators start to get warm.

What could be causing this? Do the balls themselves get distorted or worn down? Is there anything I can do without draining the system and replacing the whole valve?

Thanks for any advice!

 

[D_Hailsham]

The valve should turn easily by hand without needing a pair of pliers.

It sounds as if the valve is letting by, which suggests a worn ball.

I take it your valve is the version where the actuator can be completely removed (small bump on the cover). If so, you can get a replacement ball kit, part no 272752A/U CARD.

You have to drain down below the valve level, but you don't have to replace the complete valve.

 

[beniamino]

Thanks! That is very helpful -- replacing the ball is a job I can tackle myself, whereas dealing with the compression joints is beyond me. I will have a go!

Ben