Replacing Room Thermostat 3 wires to 2 wires??

[BlockABoots]

I currently have a Honeywell dial type thermostat installed which needs to be replaced, i have bought a Honeywell digital thermostat (DT90E).

The old thermostat has 3 wires....

https://i.*********/M1lOa7r.jpg

but this new digital one only requires 2 wires, live and switching no neutral is needed for what ever reason??.

Now im guessing the following...

Red = Live
Yellow = Switching
Blue= Neutral

is there anyway to make sure this is the case?

 

[ShaunCorbs]

1 live in
3 live out
2 neutral

 

[BlockABoots]

1 live in
3 live out
2 neutral

Ok thanks, so is it safe to just chocolate block off the blue wire then and leave it hanging behind the mounting plate?

Also why does this type of thermostat not need a neutral connection?

 

[ShaunCorbs]

Ok thanks, so is it safe to just chocolate block off the blue wire then and leave it hanging behind the mounting plate?

Also why does this type of thermostat not need a neutral connection?

yes thats fine

it increases the accuracy

 

[townfanjon]

Its an anticipator , its to prevent overshooting after the set temp and turn off slightly before .

 

[BlockABoots]

yes thats fine

it increases the accuracy

Hmm actually looking on the mounting plate of the new thermostat it does actually require neutral and not live out/switching as i was told....

https://i.*********/UTyPeNY.jpg

so it needs live (red) and neutral (blue) ???

 

[snowhead]

so it needs live (red) and neutral (blue) ???

Yes, it's powered from 240v for the display
Some Stats are battery powered.

 

[Matt0167]

also need switch live not just the live and neutral

 

[Ric2013]

The wire should terminate inside an enclosure and be insulated in some way. Realistically, while leaving it hanging will work, it cannot be considered safe. Can you not bring it inside the enclosure and stick a piece of insulated terminal strip (choccy block) around it?

If this were a gas issue, we'd say it had to be done by a registered gas installer. I find it odd how the minute one mentions DIY touching a boiler on this forum the stock answer is get a Gas Safe installer, but no one seems to care about electrics. Legally, electrical wiring of a heating system should be done by a competent person (i.e. a registered electrician), or notified to Building Control.

Rant aside, I think A is live in, B is switched live to boiler, and C becomes live when the room is up to temperature (not sure why you'd need to use C for heating). Assuming your controller is the DT90E model, the instructions to which I have just looked at. Easiest way would be to find the wiring diagram for the old thermostat (probably inside the lid) and identify the cable cores by the terminal they are connected to.

 

[BlockABoots]

Yes, it's powered from 240v for the display
Some Stats are battery powered.

This one does use 2 AA batteries!

 

[BlockABoots]

The wire should terminate inside an enclosure and be insulated in some way. Realistically, while leaving it hanging will work, it cannot be considered safe. Can you not bring it inside the enclosure and stick a piece of insulated terminal strip (choccy block) around it?

Yeah thats what i ment, just adding a chocolate block on the end of it and push it back up so behind the thermostat housing so its not visible or touchable

Rant aside, I think A is live in, B is switched live to boiler, and C becomes live when the room is up to temperature (not sure why you'd need to use C for heating). Assuming your controller is the DT90E model, the instructions to which I have just looked at. Easiest way would be to find the wiring diagram for the old thermostat (probably inside the lid) and identify the cable cores by the terminal they are connected to.

Good call, there is indeed a diagram in the case of the old thermostat....

https://i.*********/KlwYUvE.jpg

though that seems to only relate to just a 2 wire install not the 3 that is currently wired up!??

 

[ShaunCorbs]

3 live out
2 neutral
1 live in

 

[Ric2013]

Good call, there is indeed a diagram in the case of the old thermostat..

https://i.*********/KlwYUvE.jpg

though that seems to only relate to just a 2 wire install not the 3 that is currently wired up!??

I think you're wrong. You'll have to get confirmation from people more qualified than me, but I would say that in that diagram 1 is live, 3 is switched live to boiler, and 2 is neutral.

 

[Harvest Fields]

Hmm actually looking on the mounting plate of the new thermostat it does actually require neutral and not live out/switching as i was told..

https://i.*********/UTyPeNY.jpg

so it needs live (red) and neutral (blue) ???

Yes, it's powered from 240v for the display
Some Stats are battery powered.

Surely that is not right????? You don’t want to be putting neutral into terminal B!!

 

[Ric2013]

Harvest - is that your way of agreeing with me and Shaun?

See what happens when unqualified people start touching electrics? I've only tried to advise because I've known a few electricians who don't understand heating wiring at all, so the general advice to refer to an electrician would quite possibly not end well 🙂

 

[Harvest Fields]

Harvest - is that your way of agreeing with me and Shaun?

See what happens when unqualified people start touching electrics? I've only tried to advise because I've known a few electricians who don't understand heating wiring at all, so the general advice to refer to an electrician would quite possibly not end well 🙂

Yes mate. Saw his comments above and saw red. Didn’t read the rest of the post before I commented. Wanted to post before he put neutral in B. 😱😱 But have read all the post now and yes I agree with you both. I wouldn’t have wanted to be in his house when he put the power back on.😱😱😱😕😕

 

[Ric2013]

Do you reckon the fuse would have gone bang first - or the new thermostat?
And would the OP have been lucky enough to have a spectacular firework display, or a disappointingly quiet pop, with no further effect other than post 18 being 'Have tried connecting the neutral to terminal B, but it doesn't appear to be working. Any further suggestions?'?

 

[heliotrope]

Some of the information you have been given is very confusing.

Do not connect a neutral wire on your DT90.

Doing so could be dangerous.

Disconnect from the boiler connection or terminate safely at the
thermostat end.

I would suggest that you employ a competent electrician to carry out
this work for you.

 

[Harvest Fields]

Do you reckon the fuse would have gone bang first - or the new thermostat?
And would the OP have been lucky enough to have a spectacular firework display, or a disappointingly quiet pop, with no further effect other than post 18 being 'Have tried connecting the neutral to terminal B, but it doesn't appear to be working. Any further suggestions?'?

Depends what boiler it is.I have been to a couple of jobs where the gas valve has tripped the fuse box but not touched the 3 amp.

 

[BlockABoots]

I think you're wrong. You'll have to get confirmation from people more qualified than me, but I would say that in that diagram 1 is live, 3 is switched live to boiler, and 2 is neutral.

Well going but the correct colour scheme for wiring you would indeed put money on Red being live, blue being neutral and yellow being the odd one out having to be the live switching in this case.....i mean what electrician would wire it up any other way??

So just to confirm i defiantly dont want to be connecting neutral to this new thermostat and why does the thermostat have 3 terminals available?