Help wiring Honeywell DT2 thermostat

[Avo Mk8]

Ziggie It's a THR840D https://livewell.honeywellhome.com/honeywell_wp/wp-content/uploads/THR840DUK-EN-d05.pdf

 

[karatekid]

I'm not sure about this - could somebody confirm my thoughts here:

The old Honeywell thermostat needed a neutral as it has a small heater resistor to reduce the hysteresis of the bimetallic strip. Photo below of the connections. From that the grn/yel wire appears to be permanent live in, the brown wire switched live to the boiler, and blue neutral.

But the new Honeywell Home thermostat, from the OP's picture, is battery powered and acts effectively as just a switch, and doesn't require a neutral.

So I think the green/yellow should go to terminal A, and the brown to terminal B, and the neutral safely terminated and not connected to the new thermostat at all.

Karatekid - does the lid of your old thermostat have the same diagram in it as the pic below, or any other info about which terminal is which? I do believe what you have called the 'earth' wire is very likely to be mains live, so I don't recommend experimenting until we are more certain of exactly which wire is which.

Anyone?

PS If the above is correct, and you leave the wires as you first connected them, but put the grn/yel into C, I think the boiler will run when the thermostat is off, and go off when the thermostat is on!

It works!!!! Green/yellow into A and Brown into B with Blue blocked off thank you!!!

 

[Ziggie]

Ziggie It's a THR840D https://livewell.honeywellhome.com/honeywell_wp/wp-content/uploads/THR840DUK-EN-d05.pdf

Ta I thought that the diagrams didn’t add up

 

[Ziggie]

I know you will but put red/brown tape on the “earth” wire.

great that you up and running