DIY Doctor

Replacing CMT907a Thermostat With Y9120h

Postby Andyperrins » Fri Jun 16, 2017 8:45 am

I'm replacing a cmt907a (battery powered) with a y9120h (not battery powered). I've connected the Live and neutral (brown and black wires) as previously with the 907 and the unit doesn't power up, but boiler fires. There is also a blue wire which wasn't previously used and I'm wondering if this needs to added. There's also an earth whicbis obviously wired to earth. Any ideas? Thank
So I have a brown, blue, black and green yellow wires.
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