Replacing a Honeywell T40 with CMT907

[ukleeroy]

Hi,

Im replacing my old HoneyWell T40 with a Honeywell CMT907A Battery powered thermostat. The T40 has 4 wires (Earth, live and two neutral from what i can make out) where the CMT907A only needs two.

Am i presuming correctly that I have to block off the Earth and the Neutral and connect just the live and the neutral that has the rectangle symbol in the diagram.

Please see attached pic, T40 on the Left and the 907A on the right.

Im going to move cable 1 from the T40 to A on the 907A
Im going to move cable 3 from the T40 to B on the 907A
Then isolate/Block off the Earth and 2 from the T40

Thanks in advance, Lee

Untitled

• ukleeroy
• 12 Nov 2010
• 1

 

[matt1e]

yes thats correct, what's not correct is calling the cable in 3 a "neutral" it's a switched live wrap a bit of tape around it or sleeve it for future reference

 

[ukleeroy]

yes thats correct, what's not correct is calling the cable in 3 a "neutral" it's a switched live wrap a bit of tape around it or sleeve it for future reference

Thanks Matt1e, on closer inspection 3 does have a brown sheath on the cable.

 

[Taylortwocities]

Yet again, this is all covered by a very comprehensive item in the WIKI.

//www.diynot.com/wiki/electrics:how_to_replace_a_room_stat

 

[chrisjufootdo]

Hi reading the article to change a honeywell t40 to cm901 looks pretty straight forward, I have a worcester 35dci combination boiler with a mechanical clock on the front would i have to alter any wiring back at the boiler