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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3757
Experience:  Heating and Controls engineer
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We have just moved house, I have bought a CM901 thermostat

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We have just moved house, I have bought a CM901 thermostat to replace an old Sunvic TLX. The heating system is wired through a maize of junction boxes and strip connectors with old and new cables all mixed in. There is no wiring centre, how can I work out which is the live wire and which is the load wire on the Sunvic and why are there three wires? It is currently wired yellow to 1, red to three, and blue to 4. Can you tell me which wires go where on the 901.


On the existing - Terminal 1 and 3 are the link wires that fire the heating, the blue is a neutral


Use the red and yellow and place in A and B, terminate the neutral safely by cutting off and wrapping in insulation tape


You may need it again if you change the stat to a different type.

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