Replace Honewell T40 with DT92e

[pigsfoot]

Hi,
I am wanting to replace my T40 room stat with a DT92e... i thought it would be straight forward so just bought one only to find that i need a permanent live feed.

My current t40 room stat does have three wires

1 - switched live
2 - (request heat ) neutral
3 - ( no heat required ) neutral
4 - not used
Earth

The new DT92e needs

b - switched live
n - neutral
l - permanent live

then it looks like the permanent live is also connected to point A

I also have a DT90 upstairs ( our upstairs is controlled by its own room stat which is in a good position hence its a dt90 ), when i swapped this out from our old t40 i only needed two of the original three wires ( was originally wired as per above ), now it's just switched live and neutral.

I am thinking.... as the dt92e doesn't need the two switched neutrals could i use one of them and make it permanent live... trouble is i cant remember which neutral is needed ( heat on or off ).

All my cabling goes into a single junction box in my airing cupboard so i can swap bits around and will obviously label things correctly as one of the original (black ) neutrals will become permanent live... eekkkk

I know some will say just mount the sender in the airing cupboard but i want to try an avoid this as the house has been extended several times and the cupboard is quite away from where the digital room stat will be going in the living room, plus i don't really want to leave unused wiring in the walls.

Any pointers would be appreciated.

Thanks
Rod

 

[snoopy8888]

replace the t40 with a DT90.

t40
1-Live
2-neutral
3-switch live


DT90
A-Live
Neutral not required
B-Switch Live
Earth not needed