Replacing Room Thermostat 3 wires to 2 wires??

[ShaunCorbs]

A heating off terminal

Red to a
Yellow to c

Blue in choc block

 

[Ric2013]

I would imagine you could use the final terminal (C) to run air conditioning, or if for some reason your heating setup needs needs a switched live to indicate that the room stat is satisfied, you have one.

Definitely not, based on this being the DT90E model. I can't find online instructions that say, specifically DT90 (noE), so I'm assuming E is for English language? Did this notcome with instructions?

For the correct colour scheme for wiring fixed cable in the UK, until about ?2005, live was red, neutral was black, yellow, and blue were also live colours.

The reason there are 3 live colours is to allow for 3 phase systems, and because, (in the case of 3 core and earth cables as used for two-way lights and for thermostats), it would be bloody confusing if there were three red cable cores. Really, if a live colour cable core is used as a neutral it should have been tagged black (tape or a bit of sheathing) to show it is now neutral.

After 2005, we changed to the international colours of live being brown, neutral being blue, and black and grey being the other lives. UK flexible cables colours were harmonised back in the 1970s.

So, confusingly, blue and black, might be either live or neutral, depending on the context.

For this reason, many UK houses now have a mix of new an old colours and the consumer unit usually states:

I'm going to bed.

 

[Harvest Fields]

A heating off terminal

Red to a
Yellow to c

Blue in choc block

Are you sure that yellow shouldn’t be in B shaun?

 

[Ric2013]

Shaun, are you sure:

Based on this, I think yellow to B, not C, but I may have the wrong instructions...

http://www.honeywelluk.com/Documents/Installation-Guide/pdf/1072.pdf

 

[Harvest Fields]

Shaun, are you sure:

Based on this, I think yellow to B, not C, but I may have the wrong instructions...

http://www.honeywelluk.com/Documents/Installation-Guide/pdf/1072.pdf

So this time your agreeing with me then mate😛😛😛😛😉🙂 and I thought you was going to bed.😉😉😛

 

[Ric2013]

I always agree with you Harvest, except when I don't.

I was going to bed, but I thought the OP might do it wrong and have heating that only runs in the summer if Shaun is mistaken. Shaun is probably now checking and will be back soon?

Shaun and mine and your posts crossed, because I need to write an essay instead of 5 words 🙁

 

[BlockABoots]

A heating off terminal

Red to a
Yellow to c

Blue in choc block

This is is what i mean the the manual and the diagram on the inside of the shell are completely misleading as they clearly show that Neutral is to be wired up which i thought was wrong in the first place but then had second thoughts when i read the manual.....

https://i.*********/laFpKnN.jpg

Not to worry guys im not going this right now just want to be sure before i replace the thermostat

 

[Ric2013]

I think you should get an electrician in.

 

[Harvest Fields]

I always agree with you Harvest, except when I don't.

I was going to bed, but I thought the OP might do it wrong and have heating that only runs in the summer if Shaun is mistaken. Shaun is probably now checking and will be back soon?

Shaun and mine and your posts crossed, because I need to write an essay instead of 5 words 🙁

I have he same problem mate. Sometimes I am midpost, then I get distracted by the kids or the missus and by the time I actually post someone has beaten me to it.😛

 

[Harvest Fields]

I think you should get an electrician in.

Me too mate

 

[Harvest Fields]

This is is what i mean the the manual and the diagram on the inside of the shell are completely misleading as they clearly show that Neutral is to be wired up which i thought was wrong in the first place but then had second thoughts when i read the manual...

https://i.*********/laFpKnN.jpg

Not to worry guys im not going this right now just want to be sure before i replace the thermostat

They are not mis leading mate. They are perfectly clear and do not take this the wrong way but you are not understanding them at all. The new timer unit and the instructions say nothing about a neutral. Do yourself a massive favour and get a heating engineer or Sparks In to fit it for you. It’s a 30 minute job max with coffee, biscuits and a chat for a pro.

 

[ShaunCorbs]

This is is what i mean the the manual and the diagram on the inside of the shell are completely misleading as they clearly show that Neutral is to be wired up which i thought was wrong in the first place but then had second thoughts when i read the manual...

https://i.*********/laFpKnN.jpg

Not to worry guys im not going this right now just want to be sure before i replace the thermostat

Yep your right, it's the neutral writing on it that through me

Red to a
Yellow to b
Blue in a choc block

Sorry for any confusion

 

[Harvest Fields]

Yep your right, it's the neutral writing on it that through me

Red to a
Yellow to b
Blue in a choc block

Sorry for any confusion

What chance do we have if even the pro’s are making these kind of mistakes shaun?😛😛😛😛😛😛😛😛😛😛😛😛😛😛

 

[ShaunCorbs]

What chance do we have if even the pro’s are making these kind of mistakes shaun?😛😛😛😛😛😛😛😛😛😛😛😛😛😛

😀 be fine, just would only turn the heat on what ever the stat is set at eg desirable temp

 

[oz-plumber]

Re: The old thermostat, did that have a light come on when the heating was on?
If so, that's what the neutral is for.

As for the DT90, all that thermostat does is switch the active.
When the thermostat calls for heat, it sends the 240v supply back to the boiler to switch the boiler on.
Connections in the DT90 - A & B ( C is used for cooling )

All you have to do is find is the wiring connections in the boiler thermostat terminals and use those wires. If there's a neural there, cap the neutral.

 

[BlockABoots]

Ok, chocolate blocked off the blue wire, connected red to terminal A and yellow to terminal B, turned the power back on and nothing blew up!. The boiler fires up when i set the temp higher than the current displayed temp and goes off when i set it a few degrees below and pump stops running when i turn the heating off completely.

Only thing i have noticed is even if i turn the heating off the little flame icon on the LCD display of the thermostat stays on so the thermostat is still calling for heat, it only disappears if i set the temp higher than what the current room temp is. Im guess it is normal for the flame icon to still be displayed even though the heating is turned off as it is a battery operated thermostat??

 

[Harvest Fields]

The flame should go off but the display should still be on

 

[Ric2013]

Hmm. I would think it is normal, as the room stat is not intelligent enough to know if the programmer has switched off the heating.

 

[BlockABoots]

Hmm. I would think it is normal, as the room stat is not intelligent enough to know if the programmer has switched off the heating.

Yeah that what i though what with it being battery operated. The main thing is the flame disappears as soon as the target temp is reached, i just didnt know if it communicated with the programmer via the 2 wires so it knew that it wasnt on and thus stop calling for heat....but then i guess if the programmer is switched off then it doesn't matter if its calling for heat

 

[Ric2013]

Well, when the set temperature is reached, the room thermostat itself is the item that is switching off the live to the boiler (pump etc), so in that circumstance it knows what is going on.
Glad you got it going. I was concerned you were going to persist in connecting neutral to terminal C 🙂