How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Andrew Smith Your Own Question
Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3629
Experience:  Heating and Controls engineer
46681511
Type Your HVAC Question Here...
Andrew Smith is online now

We have just moved house, I have bought a CM901 thermostat

Resolved Question:

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.
Submitted: 3 years ago.
Category: HVAC
Expert:  Andrew Smith replied 3 years ago.

XXXXX XXXXX :

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

XXXXX XXXXX :

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

XXXXX XXXXX :

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

Andrew Smith and other HVAC Specialists are ready to help you