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Honeywell Mechanical Thermostat Replacement With new Honeywell D90E

Postby andreaaermones » Fri Feb 03, 2017 8:31 am

Morning all,

I m looking to replace an old Honeywell mechanical thermostat with the new Honeywell D90E.

I am a bit confused about the wiring in the old thermostat. I have 4 cables, brown, grey, black and yellow stripped. I am not sure which ones of these though need to be connected to the new thermostat. please help?

Thank you all for your time :)
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Postby GayEddie » Fri Feb 03, 2017 8:36 pm


Not sure which honeywell stat you have but if it is a T6360 there will have numbers there on old stat.

the green and yellow wire is the earth wire

#2 is the neutral wire

then the other wires will be in #1 and #3 on the old stat one of the wires will be from your clock heating on, the other goes to motorized valve and fires boiler.

Now your new stat has connectors A and B you will have to put the neutral in a block connector to make safe, not sure if you have multi meter but what you want is the wire from the clock ( either 1 or 3 on old stat ) wants to be in A and the one to boiler goes in B

Hope this helps
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