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Central Heating not Switching off When Hot Water is on With Baxi Boiler and British Gas UP2 Controller

Postby lbaker78 » Fri Nov 03, 2017 4:43 pm

I have an odd situation with our system boiler which I'm hoping somebody can give me some advice on.
We have a Baxi boiler and a British Gas UP2 controller, plus a room thermostat.
In the airing cupboard there are 2x two port valves, 1 for CH and 1 for HW, plus pump and British Gas thermostat set to 60 degrees C on the HW tank.

The basic symptom is that when the CH and HW are on together the house gets far too hot, with the radiators getting hotter even though the thermostat is off.

If the HW is on, on its own, the HW tank heats up to 60 degrees and the boiler stops firing, the pump shuts down when it should, the HW valve closes as it should.

If the CH is on, on its own, the house comes up to a nice temp, the thermostat sends the signal to shut down. As expected the boiler stops firing, pump switches off, the valve closes.

All good so far!

However, if the HW and the CH are on together, the CH will not switch off. The valve does not close when the room thermostat sends the shut down signal. Neither does the valve close if I switch the heating off manually via the advance button on the control unit. At this point within half an hour the house is very very warm and the HW tank is starting to get (normally) hot.

If I then switch off the HW, the boiler stops firing, the pump stops and weirdly, BOTH valves close.

When we first moved in to the house at the start of this year we noticed the issue and I found the valve had seized on the HW side. I assumed this to be the problem and replaced both valve unit and motor, but the problem persists.

Apologies for the long post, just wanted to provide as much (hopefully useful) info as possible. Hopefully somebody can help shed some light on the situation?
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