HW or CH but not both?

11 Dec 2003
Reaction score
United Kingdom
Seem to have a problem - javascript:emoticon(':(')

If I switch on in this order:
CH then HW ON boiler fires, turn CH off - valve moves and HW fires the boiler
If I have HW then CH on boiler fires, then turn HW off - boiler turns off
Now turn CH off and back on, the boiler fires up

Power is as follows:
Just CH - White\Grey\Orange
CH off and HW on - Orange
Both on - just Orange
Just HW - Orange

When switching CH & HW on and off, sometimes I get a good relay click other times I get a less healthy sounding click.

I have children, so could teach them to keep changing the buttons, but guess I ought to get it fixed.javascript:emoticon(':)')

Any clues? I suspect either a micro switch on the three port valve or the programmer or wiring?

Thanks :(
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sound like a dodgey relay on the valve or faulty wiring did u test from the wiring unit or the valve
"sound like a dodgey relay on the valve or faulty wiring did u test from the wiring unit or the valve"

I tested from the wiring unit - definitely don't get Orange and White
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white is from the room stat. so when house wants heat room stat kicks in giving power to white wire.

you must of had it at some stage cause you stated -

Now turn CH off and back on, the boiler fires up
Just CH - White\Grey\Orange
What are you getting on the grey wire when both HW&CH is selected?
You should get 50-110V
Hi just trying to work out your fault.
You seem to say you can get HW on its own and also CH on its own, but you can't get both at the same time. Is that correct?
When you select both HW and CH it does not neccessarily mean you get both. It all depends on existing state. In most cases you would get both when you first put them on, but it's not meant to stay like that. As soon as either mode gets satisfied the valve closes that mode off and opens the other mode fully.
If you're saying the valve never stays in mid position, that is due to the valves internal components.
Beside feeding No1 microswitch the white also feeds No2 microswitch which feeds a small pcb which produces lower rectified power. This is fed to the motor along with the white through No 1 M/S.
When the mid position is reached there are two alternatives.
No 1 M/S is triggered and the 240v supplied by white wire is dropped, but the lower rectified power is still there and will hold valve in that position. Thats is providing the grey is not live. If the grey is live then it takes over from the white wire, it then triggers No2 M/S and drops the rectified voltage (no longer required) and feeds power out through the orange.
A faulty No2 M/S or pcb could prevent the valve being held at mid position
Or it could be a hot water priority set up.
Try putting both on together and turning the cylinder stat down, if it motors to CH then thats could be the case,
Also evident if there is no connection to the HW slot on the programmer
The only thing not right is both on.

There should be 240v on the white.

so check the room stat.

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