Help please with thermostat swap...

[rdhanjal]

Hi all

I would really appreciate any help with a problem i'm having changing my thermostat.

The old thermostat is a Towerstat RS http://www.tfc-group.co.uk/assets/graphics/static/RS RCS RFS User instructions.pdf, and I've been trying to change it to a Honeywell DT90e. But so far, I've blown 4 fuses when turning it all back on!

I've put back the old one, but i think it's wired wrong as it seems to turn on the heating when you turn it down.

I wish i had taken a note of the wires before removing them, but i think the cabling was:
red - pin 1
yellow - pin 3
blue - pin 4

Using a multimeter on the towerstat, gives me the following:

call for heat [ON]
PINS
1+3 0v
1+4 240v
3+4 240v

no call for heat [OFF]
PINS
1+3 240v
1+4 240v
3+4 0v


I connected the DT90e with:

red - pin A
blue -pin B
yell - pin C


I've must've got it wrong somewhere as this blows the main fuse every time.
Anyway, I'm totally at a loss and was gonna phone the plumber, but i really think it must be a simple thing i've got wrong.

I've uploaded some pictures to make it easier to explain what i'm talking about:
http://www.flickr.com/photos/48310285@N08/

many thanks in advance
Robin
[/url]

 

[stem]

You don't need the neutral anymore. So isolate the blue wire and tuck it away. The neutral was used with older mechanical thermostats to operate a little device called an accelerator to improve accuracy. Modern electronic thermostats don't need this.

Judging from your test results, your memory of where the wires originally went is correct. You can check by removing the wires from the thermostat, turn on the programmer and you should get 230v across the red and the blue, turn off the programmer and it should be 0v

On the DT90e connect your red (live) wire to terminal A and the Yellow (switched live) to terminal B. And as I said before isolate the neutral.

What you have been doing by connecting the blue to the other side of the contact, is joining the live and neutral together when the contact changes over. No wonder the fuse blew. After doing this four times you will be lucky if you have not damaged the contact in the thermostat.

 

[rdhanjal]

it worked!!!

thanks a lot for your help, luckily the stat seems fine...
...shame about the rest of my inefficient boiler system

cheers

 

[rdhanjal]

Thanks again with the help earlier, this forum is excellent.

Slight problem since yesterday though is I've noticed that the boiler kept on coming on every now and then throughout the night, even though the Danfoss 102e7 programmer (http://www.plumbnation.co.uk/site/d...gp-mini-programmer-087n653400/102E7 Guide.pdf) was set to off.

I guess it could be damaged after I blew the fuses so often.
Luckily I have a tempus six programmer handy, so i'm thinking of swapping it.
Trouble is that I'm stuck at the first hurdle, i can't remove the Danfoss unit...! I've unscrewed the the holding screw underneath but it won't lift off. Any ideas?

A bit of background to my heating system...
The plumber tells me it's gravity fed. There's a pump next to the boiler and another in the cupboard above. I don't think there is a valve to seperate HW and CH, and the HW cylinder doesn't have a thermostat on it. It's an inefficient system that just seems to regularly heat up my hot water (and indirectly the rads) whether the house needs heating or not.

I hope I've made sense. I uploaded a few more pics to aid my description (http://www.flickr.com/photos/48310285@N08/?saved=1). Again, any help is really appreciated.

thanks
Robin

 

[stem]

Slight problem since yesterday though is I've noticed that the boiler kept on coming on every now and then throughout the night, even though the Danfoss 102e7 programmer was set to off.

You probably switched the heating on there (rather than at the thermostat as I assumed) when the fuse blew and so welded the contact together then. On the plus side it saved your new thermostat.

I can't remove the Danfoss unit...! I've unscrewed the the holding screw underneath but it won't lift off. Any ideas?

If my memory serves me correctly, try sliding it upwards rather than pulling it forwards. There are several insertable pin / spade connectors holding it in place. I would recommend getting another Danfoss though. That way you won't have to change any wiring.

 

[rdhanjal]

A good idea to replace with a danfoss, i guess it would be less hassle.
I've tried lifting it off, but no luck, it just doesn't wanna come off. I've tried wriggling it slightly, but it doesn't seem to give.