Central heating trouble with motorised valve

[Murmansk69]

My central heating system has an electric valve in it, which controls whether the hot water produced by the boiler goes to the radiators, to the tank to heat water, or to both.

A few years ago I had to replace the valve because it was sticking and now it's doing the same thing again. I noticed at B and Q that you can replace just the motor within the valve rather than the whole lot, so I did that. It seemed to sort it at first but after a few hours it became clear the problem is still there.

I'm wondering if the valve contains some sort or circuitry that controls how the thing operates - I guess it must because it seems able to tell the valve motor to operate - and I wonder if it could be that that circuitry has gone, in which I will need a whole new valve?

It seems to me that the valve itself is working in that I can move it manually using the lever, and I live in a soft water area so it can't be blocked with hard water deposits.

What happens is that the valve tends to stay in the position for hot water only, even when the hall thermostat is calling for heat - I can push it into the middle position with the lever. In the morning when everything is cold, it comes on and heats the water but leaves the radiators cold.

Any ideas please?!

[Dark Angel]

It could be that the valve spindle itself (not the motor) is sticking owing to sediment/scalle build up inside. Remove the motor and twist the spindle with a spanner/pliers back and forth, round and round until it feels nice and loose. Then replace the motorised valve head and see if that makes a differance.

[Murmansk69]

[Ed Sirett]

Perhaps you could try the Main FAQ on heatign controls.

[Harry Bloomfield]

Murmansk69 expressed precisely :

After a few years of use (and heat), the moving part within the actuator does tend to bind within the fixed part of the actuator. Take the actuator off and double check that the actual valve really is free. It should be possible to turn it with just slightly more than your bare fingers (pliers).

Other possible failures are the micro-switches which are cheap to replace - Maplins sell them for around £1 each. These determine the position of the valve and trigger the pump/boiler, depending upon scheme used.

[Set Square]

There's nothing electrical in the valve itself - it's just a paddle, operated by the spindle sticking out of the top, which directs the flow to one or other or both outlets.

Remove the actuator from the wet part of the valve and make sure that the spindle is free. You should be able to turn it with finger and thumb or, at any rate, with light pressure from a pair of pliers.

Then put the the actuator through its paces while removed - and make sure that it moves to each of the 3 positions according to whether HW only, CH only or Both is selected.

If the actuator isn't moving when it should, there are 3 possible causes - each of which needs to be investigated:

• actuator motor failure

• internals of actuator jammed

• external wiring fault

It's important to make sure that your wiring is the same as that shown in the Y-Plan diagram on the Honeywell web site (I usually give the URL, but it doesn't seem to work today!). the important thing is that there must be a HW-off wire from the programmer, and the cylinder stat must have a changeover switch which feeds a 'satisfied' signal to the valve - otherwise the boiler won't fire in CH-only mode.