Help wiring Honeywell DT2 thermostat

[karatekid]

Hi all

I've purchased the Honeywell DT2 digital Thermostat to replace my old analogue honeywell one. I have a brown (live), blue (neutral) and earth. I have connected the Live to A on the Thermostat and the neutral to B. The thermostat clicks and kicks in but doesn't turn my boiler on. I've also swapped the wires around but no luck and the instructions are too complicated for a DIYer like me.

Can anyone assist please?? Photos below

https://www.dropbox.com/s/5ymldsrqz8158z1/20201128_151632.jpg?dl=0

https://www.dropbox.com/s/8rhtdzbyfeljjkm/20201128_150450.jpg?dl=0

 

[westward10]

If you definitely only have the brown and blue ignoring the earth then blue is not neutral. Connect blue to C but only if you definitely have a brown and blue.

 

[karatekid]

If you definitely only have the brown and blue ignoring the earth then blue is not neutral. Connect blue to C but only if you definitely have a brown and blue.

Brown, blue and earth as below..

 

[westward10]

Ignore my earlier post. Where was the earth connected at the old stat as it has red tape on it indicating it has been used as a live or it is just taped up to keep it out of the way.

 

[karatekid]

Ignore my earlier post. Where was the earth connected at the old stat as it has red tape on it indicating it has been used as a live or it is just taped up to keep it out of the way.

I taped it up to keep it out of the way. On the old analogue it was like this..

 

[westward10]

Looks like someone has used the green/yellow (earth) as the live return. Not ideal but if the earth is connected to C it should function. Ensure blue is in B and brown in A.

 

[karatekid]

Looks like someone has used the green/yellow (earth) as the live return. Not ideal but if the earth is connected to C it should function. Ensure blue is in B and brown in A.

Thanks ever so much. I'll hook it up tomorrow and see if it works. I'll report back either way. Thank you!

 

[westward10]

On the old stat is the terminal marked where the earth is.

 

[karatekid]

On the old stat is the terminal marked where the earth is.

I'll have a look tomorrow as ive had to connect it back. All the connections on the old stat are numbered 1-5 or 6 i think

 

[karatekid]

Do you think wiring in the earth will make it work? Or could it have something to do thing the programming box next to the boiler that isn't compatible?

 

[westward10]

I am 99% certain the earth should go into C.

 

[Avo Mk8]

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!

 

[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!

Yes its exactly the same inside. The earth is connected to number 1 on thr old stat. Ignore the red tape, I put that on.

 

[Avo Mk8]

OK, thanks for that.
Well unless the original owner didn't wire it correctly, that indicates your grn/yellow wire is mains live (so keep the red tape on it - or make it brown!), and the brown is the switched feed to the boiler. Those are the only two you need to connect to your new thermostat. As per my post grn/yel to 'A', brown to 'B', insulate the blue and don't connect it.

It would be wise to check this hypothesis first. Do you have a multimeter to check volts on the 'earth' wire? Care needed obviously.

Given that the old thermostat connected grn/yel to brown to make the boiler work, I believe the above will work.

 

[Ziggie]

This is battery powered to the only live in is from the programmer.

i cannot get a copy of the install manual as the Honeywell site is not providing it.

Do you have a copy?

do you have a Y or S system.?

(the y system has a 3 way valve while the S system has two separate valves.)

do you have a wiring system box with all connections within it? It would be easier to check the wiring from there and do you have volt meter and happy with using it?

 

[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