Plumbing: Motorised Valve Case Really Hot When Pipes Are Cold

[OceanTragic]

Does this sound like its faulty? Could it be causing my heating problems?

Quite often we don't have any hot water or central heating (like now) and after reading lots of posts I checked my motorised valve override slider.

The slider has up and down movement but has no resistance when moving it. It can be put at the top but if touched lightly falls to the bottom. Up or down makes no difference to any heating, only disconnecting the power to the heating supply for a minute occasionally makes it work again.

Thanks for any help you can give me.

[Andrew Gabriel]

If this is a 3-port mid-position valve, the usual setup is with the spring-return position being hot water cylinder, and far position being the central heating.

It sounds like the valve is driven fully to the heating position. Does it return to the spring-return position if you disconnect the power to the heating system? This should present resistance to the manual slider.

[OceanTragic]

Cheers for your reply.

After a bit of playing around it seems that no matter where I put the slider when the system is off, switching either HW or CH on makes no difference to the position of the slider.

Also when I try to put the slider in the center it just drops down to the bottom with no resistance.

[OceanTragic]

Forgot to add...

Any ideas why the plastic case is hot? Is this normal?

[Derryck Croker]

The motor bit inside the valve is continously energised (when the ch/hw is on), so it will get hot.

I'd be inclined to inspect under the cover of the valve, and see how/if the mechanism reacts when ch, hw or both are activated. Possibly there's a problem with the cylinder and/or room stat.

The Honeywell valve I have has a notch into which the manual lever can be dropped, it is released from there and positioned under motor control once automatic operation is under way.

[Andrew Gabriel]

It may be that the actuator has got too stiff. As Derryck said, you are probably going to have to look under the cover (having disconnected all the power). In some circuits, when central heating is required, the motor drives the actuator to the far end, which operates a microswitch which turns on the pump/boiler. If the actuator is too stiff, it might not get far enough to operate the microswitch, or the microswitch might have failed.

The spring should be able to return the actuator, except that if the system is switched off with the actuator in mid-position, it can remain there until touched. (The unit requires power to degauss the motor after locking the actuator in mid-position, without which it can stay locked in mid-position.)

The manual slider is not normally connected directly to the actuator, and loose slider usually means the actuator is already in the mid or far positions. On some 3-port valves, the slider can only lock the actuator in the mid-position, and on others it can lock in the mid- and far-positions.