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?

 

[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

 

[Harvest Fields]

If you turn the temp down low enough it should still go off?

 

[BlockABoots]

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

Nah, i came across a few other threads on different forms who had the same colour wires as mine and every replied said to connected red to A, yellow to B and terminate the blue

 

[BlockABoots]

If you turn the temp down low enough it should still go off?

Yeah if i lower the target temp below the room temp the flame disappears and the boiler goes off

 

[Harvest Fields]

Yeah if i lower the target temp below the room temp the flame disappears and the boiler goes off

Then what’s the issue?

 

[BlockABoots]

Then what’s the issue?

I was questioning if the digital thermostat should still be displaying the 'calling for heat' icon (flame) when i had turned the heating off or if it should disappear