Want to change my old Honeywell thermostat

[Nik0967]

Hi

Sorry for the delay in getting back with your request for a picture

Please see attached a pic of the thermostat in question

Many thanks

Nik

View media item 43366 View media item 43367

 

[D_Hailsham]

Please see attached a pic of the thermostat in question

Thanks for Pic; it's certainly an old stat.

So 1 is brown, 2 is blue, 3 is green/yellow and 4 is unused. The standard Honeywell wiring is 1 = Live, 2 = Neutral, 3 = Heating ON, 4 = Cooling ON. So it looks as if the green/yellow is being used as the switched live to the boiler.

You can check this with a meter (or even a neon screwdriver). 1 should be live all the time (when heating on at timer); and 3 only when the stat is turned up.

If this is correct, then connect the brown to DT90E terminal A and the green/yellow (marked with red insulating tape or sleeving) to terminal B. The blue wire is not used and should be terminated in a connection block.

 

[Nik0967]

D_Hailsham

Many thanks for your help

I tested the stat with a neon screwdriver and it appears to be just as you say. The brown is live when I turn the heating on. And the Yellow/Green is only live when I turn the thermostat up.

I have ordered the honeywell thermostat so it should be here in a couple of days.

 

[vicvapour]

Please see attached a pic of the thermostat in question

Thanks for Pic; it's certainly an old stat.

So 1 is brown, 2 is blue, 3 is green/yellow and 4 is unused. The standard Honeywell wiring is 1 = Live, 2 = Neutral, 3 = Heating ON, 4 = Cooling ON. So it looks as if the green/yellow is being used as the switched live to the boiler.

You can check this with a meter (or even a neon screwdriver). 1 should be live all the time (when heating on at timer); and 3 only when the stat is turned up.

If this is correct, then connect the brown to DT90E terminal A and the green/yellow (marked with red insulating tape or sleeving) to terminal B. The blue wire is not used and should be terminated in a connection block.

I in no way wish to argue with your advice Mr Halisham I do feel that I must point out that use of the CPC as a live conductor contradenes
BS7671 reg 514.4.2

The bi-colour combination green and yellow shall be used exclusively for identification of a protective conductor and shall not be used for any other purppose.

 

[Nik0967]

vicvapour

Thank you for your input regarding my questions

In light of your comments would you be able to advise on how I would wire my existing wiring to the honeywell DT90E thermostat

Thank you
Nik

 

[vicvapour]

vicvapour

Thank you for your input regarding my questions

In light of your comments would you be able to advise on how I would wire my existing wiring to the honeywell DT90E thermostat

Thank you
Nik

What boiler do you have my friend?

 

[D_Hailsham]

I must point out that use of the CPC as a live conductor contravenes BS7671 reg 514.4.2

The bi-colour combination green and yellow shall be used exclusively for identification of a protective conductor and shall not be used for any other purppose.

Yes, I do know that. Maybe you should tell the many installers who make a habit of using the CPC as a live conductor.

I did think of telling the OP to use the blue as the switched live. But that would have involved identifying the other end of the wire, which may not be easy.

 

[vicvapour]

I must point out that use of the CPC as a live conductor contravenes BS7671 reg 514.4.2

The bi-colour combination green and yellow shall be used exclusively for identification of a protective conductor and shall not be used for any other purppose.

Yes, I do know that. Maybe you should tell the many installers who make a habit of using the CPC as a live conductor.

I did think of telling the OP to use the blue as the switched live. But that would have involved identifying the other end of the wire, which may not be easy.

I know my friend, internet diagnosis, is notoriously difficult sometime, as its been said here many times before, nothing beats actually being in front of the boiler / thermostat.

 

[Nik0967]

Hi guys

The boiler I have is a Glow Worm Micron. There is a label on the front wich says 40FF. I don't know if that is any help.

Many thanks

Nik

 

[vicvapour]

Brown wire goes into A on the DT80e

Blue wire which must be sleeved BROWN, connects into Switched live (marked Ls) on your boiler.

The neutral of your boiler connects back to the FCU.

Make sure the FCU is fused at 3 amps.


O

 

[D_Hailsham]

Brown wire goes into A on the DT80e

Apart from the fact that it's a DT90E, that's correct. (10/10)

Blue wire which must be sleeved BROWN, connects into Switched live (marked Ls) on your boiler.

You have ignored the fact that the installation will have one or two motorized valves, so the call wire from the stat will not connect directly to the boiler. (0/10)

 

[vicvapour]

Brown wire goes into A on the DT80e

Apart from the fact that it's a DT90E, that's correct. (10/10)

Blue wire which must be sleeved BROWN, connects into Switched live (marked Ls) on your boiler.

You have ignored the fact that the installation will have one or two motorized valves, so the call wire from the stat will not connect directly to the boiler. (0/10)

Ah right, I forgot about that, so the switched live goes back to the 10 way then?

 

[D_Hailsham]

You have ignored the fact that the installation will have one or two motorized valves, so the call wire from the stat will not connect directly to the boiler. (0/10)

Ah right, I forgot about that, so the switched live goes back to the 10 way then?

Correct. You then have to identify if the OP has an S Plan or Y plan as this determines which colour valve wire to look for (S = Brown, Y = white), so you know which terminal the other end of the cable from the stat is connected to, etc etc.

 

[Nik0967]

Hi

Would you like me to provide anymore information to enable me to correctly wire up the new thermostat without any errors

Many thanks

Nik

 

[vicvapour]

Is your system a Y plan or an S Plan?

Y plan has 1 three port valve

S plan will have two or more 2port valves on the system.