Heating not switching off

[sammerano]

Hi,
The central heating system in my house consists of an electronic programmer, and split circuits for up and downstairs.

The first problem I had was in October, upstairs wasn't heating at all, I found out that the motorised valve for the upstairs circuit had failed (the electrical part). I bought one for around £35 and all was sweet.

Since then I noticed that downstairs was heating all the time, even if only upstairs was selected on the programmer. Also the heating wouldn't switch off, even when it was all turned off on the programmer, the boiler just kept going until I turn off the trip switch for the central heating.
I think that maybe the motorised valve for downstairs is stuck open. When I check it, the electrical part of the valve is working okay (its a Horstmann btw), but the little spindle which it attaches onto just spins right round. I take it this valve is faulty?

Also, i'm wondering will the valve staying open cause the boiler not to stop? Or do I have an electrical problem also?

Thanks in advance.

 

[stem]

I assume you are referring to a two port motorised valve. When a mains voltage is supplied across the live & neutral, the motor slowly winds the valve open. At the end of its travel, the valve operates a microswitch that is connected via the grey and orange wires to the boiler, switching it on. At the end of its travel, when the valve can go no further, the motor stalls, but because is remains energised, keeps the valve in the open position.

When a thermostat or programmer, tuns off the power to the valve, a spring pulls it back to the closed position.

You can test a two port valve as follows, Only do this though if you are competent to do so. Disconnect the valve from the wiring (make sure you note where the wires have come from so that you can put them back afterwards) and connect the brown wire to a live supply and the blue wire to a neutral (if there's an earth make sure thats connected too) The easiest way may be to put a plug on the end with a 3A fuse in (make sure the grey and orange wires are left out for testing) Then plug it into an extension lead and see if the valve opens. If it does, remove the supply and check that it closes. If you connect the grey and orange wires to a multimeter measuring resistance, whilst operating the valve, you should see the circuit open and close as the microswitch operates.

BTW £35 seems cheap for a new motorised valve.

 

[sammerano]

Thanks for the response. I think it is two-port all right, its on a in-line piece of pipe (not a tee junction). It was the blue plastic part I bought, not all the pipework, if that makes sense. Sorry i'm not a bit more knowledgeable!
There is a small silver lever on the valve for overriding the electrics, and leaving it open. When I switch it on I can hear the valve moving and there is no resistance on this lever, and when I switch it off the resistance is back. This is why I thought this part of the valve is working okay, although maybe it's not switching off the microswitch.

 

[powell30]

It is possibly faulty and letting by, or your wiring is wrong and the system is doing what it should according to how it's wired

 

[sammerano]

Should the spindle on the pipe part of the valve be able to spin round 180 freely? If I turn it, say, 1/4 turn manually it doesn't seem to close the valve.

 

[Agile]

Some older types will do that.

Many of that type only turn the motor in one direction. They have to be positioned exactly to close the port.

Tony

 

[sammerano]

Thanks, its just that if I take off the head of the other valve (for upstairs), the spindle only turns about 1/4 turn from side to side and stops.

 

[stem]

There is a small silver lever on the valve for overriding the electrics, and leaving it open. When I switch it on I can hear the valve moving and there is no resistance on this lever, and when I switch it off the resistance is back. This is why I thought this part of the valve is working okay, although maybe it's not switching off the microswitch.

I'm not familiar with a Horstmann valve, but other types don't operate the microswitch when operated manually. The lever is really there to open the valve when filling the system with water, so you wouldn't want the boiler firing anyway.