Faulty motorized valve body

on 29/08/2014, asalcedo supposed :

Are you certain it is the valve, rather than the actuator?

Could you maybe borrow an actuator from a another zone, to double check the operation. The reason I suggest it is that the actuators are much more troublesome than the valves.

Is the spring intact? The motor only opens the valve, it's the spring that closes it.

As I mentioned, I have tried a brand new motorized head, but still, when the lever moves to the Auto (closed) position, the valve still lets hot water through.

I agree that the heads are far more likely to fail than the valves. In the last 10-12 years I have had to change two or three heads, never a body. However, this system is over 15 years old, so the valve bodies have already lived long.

If I do have to change the body, I am inclined to do so with the other four in the house, they are not expensive and I don't want to be draining too often.

Graham. submitted this idea :

If it is the spring type, this type fails with quite alarming regularity, but never have I seen the springs break. More often they simply jam through wear, or the micro-switches fail - sometimes the motors fail.

As said, try a replacement actuator.

I replaced the old motorized head with a brand new one.

The new seems to work fine, the lever can be moved to the manual open position and then, when released, moves all the way back to the closed position.

Can I conclude that if the valve does not close with a new head, it is the valve body that needs to be replaced?

asalcedo explained on 31/08/2014 :

I'm not sure I understand..

In your first paragraph you said the new one works fine, then in your above paragraph you are asking if it might be the body again.

Of course if the new head doesn't fix it, the valve body has to be passing.