Honeywell ST9400c - hot water but no heating

12 Mar 2013
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United Kingdom
We're having an issue with our heating, but it doesn't seem to affect the hot water.

The hot water will run fine, pump running, valve making a little whirring noise when moving, and offering resistance when pushed backwards (and perhaps most obviously, there's hot water).
When you turn on the heating, the little green light on the controller comes on, but that's it. Nothing by way of pump activity, no little whirring noises, and no heat. I've almost 100% discounted the room thermostat, which despite being wireless has reassuring lights and the receiver unit makes a satisfying click if you crank it right up to discount that being an issue.

Lose wire(s)? Controller fault? Wireless thermostat is rubbish?
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Most probably a valve fault.
What valve/valves have you got 1x3 port or 2x2 port ?

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