New Thermostat wont work

[chrisroffey]

Hi,
I'm trying to fit a new thermostat but it wont work. This is the third one I've tried but they either work at random or as this latest one is doing the heating constantly stays on even when it's turned down to the minimum temp. It is a Honeywell DT90e thermostat with a Potterton EP4001 timer switch and a Baxi Solo 70PF boiler. The wires at the thermostat are L (red) N (black) and earth. Please help, driving me nuts.[/img]

 

[seco services]

doubt that black is neutral.

what terminals have you put the wires in ?

 

[chrisroffey]

Red in A and Black in B.

 

[seco services]

thats ok.
red live from programmer
black sw/l to mot valve.

when the stat is turned down below room temp does the black have any voltage reading ?

what type of motorised valves have you ?

 

[chrisroffey]

I'm not really clued up on all that stuff and dont have the gear. It was just that the old thermostat had seen better days and thought I'd change it when we redecorated. I assumed it would be a straight swap. I first bought a digital one that didnt work, then I swapped it for a Honeywell manual dial type which had pretty much the same terminals as the original one (1,2,3,4 and Earth) but that didnt seem to work the heating properly. I then read that the DT90e was a straight swap for a three wire thermostat so I bought that but the heating just runs buy the timer switch now and ignores the thermostat.

 

[seco services]

you've wired it ok.
does the heating cut out if programmer heating turned to off ?

does the heating cut off if you push and hold the on/off button on the stat ?

 

[chrisroffey]

Boiler comes on and off with the timer switch but if I put the programmer to constant and then turn the thermostat on and off or up and down it has no effect on the boiler. It just keeps going.

 

[chrisroffey]

This was the old one [img

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• chrisroffey
• 12 Jan 2011
• 1

][/img]

 

[seco services]

does the heating cut off if you push and hold the on/off button on the stat ?

does the little flame on the stat go out when you lower temp and boiler stays on ?

 

[chrisroffey]

No, the boiler keeps running. The flame on the display comes on and off when it is turned on and off or up and down and you can hear the click in the stat when you turn the temp past the room temp.

 

[seco services]

need to check with a multi meter really to see if the black is always powered.

or take the black out of terminal. heating shouldn't come on.

 

[chrisroffey]

The stat also displays the flame and clicks when turned up evne when the boiler is set to off on the programmer. Am I right in thinking that if the boiler is on constant it will run as long as the room temp is lower than the temp set on the stat and it will go off when it rises above it. So if I turn the temp up and down I should hear the boiler switching on and off?

 

[seco services]

The stat also displays the flame and clicks when turned up evne when the boiler is set to off on the programmer.

thats ok.

Am I right in thinking that if the boiler is on constant it will run as long as the room temp is lower than the temp set on the stat and it will go off when it rises above it. So if I turn the temp up and down I should hear the boiler switching on and off?

yes

 

[chrisroffey]

So why did it work with the old stat but not with the other 3 I have tried. I haven't changed any wiring in the programmer. Thats whats baffling me!
Thanks for your help on this. I'm going to try and get my hands on a multi meter at work tomorrow.

 

[seco services]

can't answer that.
but a multi meter should be able to.