British Gas RS1 Room Thermostat Replacement

[Malcolm Jordan]

My existing British Gas RS1 room thermostat is in the hall and as I understand my central heating room temperature is controlled by this thermostat. The boiler is a Gloworm Ultimate and the heating and hot water programmer is a Honeywell ST6400C.
The RS1 is not too accurate and I wish to replace this with a Honeywell DT90E, this should give greater accuracy whilst, hopefully, retaining simplistic operation (I am a bit of a simpleton)

This is the wiring for the RS1, there is also an earth wire arrached to the back of the box.
Blue is neutral(N), red is live(L), yellow is attached to at terminal (3)

This is the Honeywll DT90E wiring terminal. It 3 connectors with screws A, B and C

I have tried wiring the DT90E as follows Red wire to terminal A (L), Blue wire to terminal B (N) and yellow wire to terminal C. The i turned the power on it tripped and blew the fuse at the socket which served the central heating programmer.

Looking on line it seems that I may only need to connect the new thermostat to 2 wires.

My question, how to I wire the new thermostat, which wire should go to terminal A, which wire to terminal B, if any, and which wire to terminal C, if any. Hopefully someone can help and thanks in anticipation. I am sure if I knew what I was doing it is relatively simple, for now I have put the RS1 back and all is working as it did.

 

[stem]

Existing thermostat Red wire = Live = Honeywell A
Existing thermostat Yellow wire = Switched Live = Honeywell B
Existing thermostat Blue wire = Neutral = Not required by Honeywell insulate / isolate it and tuck it safely our of the way. (I would put it in a separate new screw connector)

The Honeywell is double insulated so no earth connection is required to the thermostat. If the back of the box you refer to is a metal box behind the thermostat leave the earth wire connected to it.

Don't connect anything to Honeywell C.

 

[Malcolm Jordan]

Stem, thanks for the reply, will give it a go tomorrow. Mrs J is fuming at the mo so will leave it working as was till she goes to work tomorrow, told you I was a simpleton. The very thought of not using a neutral would not have occurred to me. I very much appreciate the speedy reply, I will screw the blue to a connector to keep it from touching anything and tuck well out of the way.

 

[flameport]

Red wire to terminal A (L), Blue wire to terminal B (N) and yellow wire to terminal C.

That has probably destroyed the new thermostat.

 

[stem]

Yes it may well have done.

A short circuit can tend to weld the contacts together, so you might find that it's permanently 'on' now. Sometimes if it trips an RCD I've known contacts survive, and occasionally blowing a 3A fuse, not a 13A fuse though.

 

[Taylortwocities]

Try connecting the red to the yellow in a bit if insulated terminal strip.
Isolate the blue.

Then check the boiler still works when you turn on the programmer. If it doesn’t you may have scrogged the programmer.

 

[AndyPRK]

If you have broken 2 items, this maybe time to purchase a programmable thermostat which sets different temperatures for different time points during the day. (or maybe your new one does that)

Keep the old timer to control the hotwater if necessary. That part may still work

 

[Malcolm Jordan]

Good morning and thank you for all the contributions. The good news is the DT90E is installed and working as I hoped it would. Thanks again to Stem for your advice, it worked. To the rest who have replied I am very grateful, had it not worked I would never have considered the suggestions made. AndyPRK thanks for the suggestion time for me to sit down with a cup of tea and see exactly what the DT90E can do, however, so long as the programmer comes on, it does, and the thermostat regulates the temperature, it does, then I am a happy bunny.

Moral of the story, nothing in the UK appears standard, i need to stick to basics like changing lamps and basic 3 pin plugs where needed. The rest seek the help of those of you that know before not after the event. I got away with it this time next time I may not be so lucky. Thanks to all.