Need help with installing replacement room thermostat

[joolsm]

Hi, we are in the process of replacing an old slider-style room thermostat with a digital one (Honeywell DT90E). We have replaced it and wired it in, but it seems to be having no effect at all on the central heating! The heating just carries on working at full blast even though the current temperature shows as being much higher than the temperature it is set for. Any ideas? Thanks for any advice

 

[ban-all-sheds]

My guess is that you've wired it wrongly.

 

[joolsm]

My guess is that you've wired it wrongly.

The old thermostat had old-style wiring - 2 red wires and a black. At the moment we have the 2 red wires wired into the unit and the black wire is sealed off (sorry if that's the wrong terminology!)

 

[Iggifer]

there's a number of wiring diagrams for the DT90E depending on your set up. Which one (a-f) did you follow? Or was it guess work?

 

[joolsm]

there's a number of wiring diagrams for the DT90E depending on your set up. Which one (a-f) did you follow? Or was it guess work?

Guess work I think, none of the diagrams seemed to apply to the wires I have

 

[Iggifer]

do you have one wire in A and one wire in B?

 

[joolsm]

do you have one wire in A and one wire in B?

Yes

 

[Iggifer]

then just swap them round.

Sounds like you have the permanent live and switched live the wrong way around

If you have a tester, you want the perm live in A and the sw live in B

//www.diynot.com/wiki/electrics:how_to_replace_a_room_stat

The baseplate is arranged differently but the diagram on the baseplate will help you understand

 

[joolsm]

then just swap them round.

Sounds like you have the permanent live and switched live the wrong way around

If you have a tester, you want the perm live in A and the sw live in B

//www.diynot.com/wiki/electrics:how_to_replace_a_room_stat

The baseplate is arranged differently but the diagram on the baseplate will help you understand

We have tried various permutations, not sure if we have swapped the 2 reds without the black one also being attached though. Will give it a try and get back to you. Thanks for the advice so far, was not sure if it was a wiring issue or something to do with the boiler.

 

[Iggifer]

if swapping the two reds doesn't work you will need to do more investigation to get it sorted, you don't want to blow up your fancy new stat

 

[joolsm]

if swapping the two reds doesn't work you will need to do more investigation to get it sorted, you don't want to blow up your fancy new stat

Still no change when we swap the 2 reds around - radiators come on full blast even though the temperature is showing as 25 and the set temperature is 18 degrees.

 

[flameport]

We have tried various permutations

Did one of those involve a fuse blowing and then being replaced?
Possible that the thermostat has already been damaged by incorrect wiring.

 

[joolsm]

We have tried various permutations

Did one of those involve a fuse blowing and then being replaced?
Possible that the thermostat has already been damaged by incorrect wiring.

At one point we needed to change a fuse on the CH timer socket, which went off. Could this have damaged the new thermostat, which is in another room?

 

[joolsm]

Actually, after the latest attempt at wiring it, the boiler has now gone off. We are now waiting for the temperature on the thermostat to drop down a couple of degrees until it hits the set temperature. Hopefully if the boiler kicks back in at this point, we are sorted. Thanks for advice so far

 

[joolsm]

Woohoo, the boiler did kick in when the temperature fell! Thank you for your advice. The only concern I still have is that the thermostat is showing the current in-house temperature to be 26 degrees - I am not convinced that is correct, but will monitor over the next few days. Thanks again