Wiring a Thermostat, help please!

Hello all,

Trying to wire in a new digital room thermostat ( Honeywell DT4) to replace my old BG R2 dial style one for a non combi boiler.

Currently there is a programmer fitted by back door (permanently set to on)and R2 fitted in living room which is used to control heating temp as required.

Problem is that when R2 cover removed there is 3 wires (and earth) and new DT4 only requires 2.

The earth isn’t an issue but the confusion arises from the unclear and differing wiring diagram’s provided with new unit.

The current 3 wires are Red, Yellow and Blue wired to Live, 3 and Neutral as in first diagram below.

Second diagram is on the instructions but third diagram is on a sticker inside the unit.

How should it be wired? Any help would be very appreciated 😊

Sorry, second photo was too cropped🙄

I would connect Red to A; Yellow to B; and Blue (safely) not connected to the thermostat. I am not a heating engineer.

Looks like your new stat doesn’t need a neutral.

As per  @sl2000 

https://forums.overclockers.co.uk/threads/room-thermostat-wiring.18883361/

Cheers,

Probably should mention that the new thermostat is battery powered so maybe doesn’t need a live feed? Dunno, I’m a bit of a numpty with these new fangled contraptions 😊

Could probably get an electrician in but if it’s a simple thing I’d rather not.

Probably should mention that the new thermostat is battery powered so maybe doesn’t need a live feed?

It needs live as that is what it connects (via a relay) to the output to power the boiler.

It’s a single pole switch, Live in, Switched Live out.

The thermostat is battery-powered so doesn’t need a L & N to run, however it does need a L as that’s what it sends to the boiler to cause it to fire (from terminal B). The three-core cable going to it then just needs the red (permanent L) and yellow (switched (by the stat) live) utilised, put the blue in a connector block (Wago) and push it into any space in the back.

I’ve an old bimetallic thermostat in the hall. Is this a replacement for that sort of thing?

Don’t worry OP this happens to me every time I want to wire something in. It always seems like it should be simple, and it never is!

I might post my confusing smoke alarm wiring set up and see if folk can help me replace the existing alarms with modern ones though.

I’ve an old bimetallic thermostat in the hall. Is this a replacement for that sort of thing?

Yep.

Thanks to all for the help👍

As described above turned out to be Red A, Yellow B 

Good to know people are willing to help a numpty out, Cheers😊

Helped me too, bought same after old one went a bit off the rails. All good now.

@nstpaul is the dt4 working for you? Mine doesn’t seem to be holding temp. Set to 16 but just rises the temp to 18-19. Today it’s set at 16 but has read 19 all day.

Yeah works fine for me. Try setting it for 25 and see if it clicks and starts your boiler. When the boiler is on it will show a little flame on the display when you touch the button to light it up. Sounds like the ambient temperature where it is located is 19 possibly so not actually doing anything if set at 16🤷🏻‍♂️ That’s about the limit of my knowledge so hope you get it sorted👍

I might post my confusing smoke alarm wiring set up and see if folk can help me replace the existing alarms with modern ones though.

Just what we need, amateurs bodging safety systems…