Wiring a Drayton Digistat 3 room thermostat

[DIY_Guy]

Hi all,

I recently bought a new digital room thermostat to replace the old one that was in my hall. The new one (Drayton Digistat 3) says that it replaces most standard room thermostats but I'm having problems with the wiring.

The wiring schematic for the new thermostat has -

1. Common
2. Heating satisfied
3. Call for heat

It also says that if the old thermostat used a neutral and/or earth supply, these should not be connected and should be safely isolated. The old one had a red wire(live), blue wire(neutral?) and yellow wire(switched live?) Does this mean I should only connect the live wire? If so does anyone know where I should connect it (common, heating satisfied or call for heat)?

My old thermostat was a honeywell. The red wire was connected to 1, blue to 2 and yellow to 3. I have checked and there is permanent live in the red wire and the yellow wire has some current running through but not as much as the red wire.

 

[bernardgreen]

RED Live to common

YELLOW Switched Live to Call for Heat

BLUE Neutral to a terminal block

Earth to another terminal block

 

[RF Lighting]

Look whats in the wiki.

A step by step guide with full colour pictures

Amazing



//wiki.diynot.com/electrics:how_to_replace_a_room_stat[/wiki]

 

[DIY_Guy]

Hi,

Thanks for the swift response.

The wiring instructions say not to use the neutral (blue) or an earth( i dont have one)

I connected red to 1 (common) and yellow to 3 (call for heat) and isolated the blue wire. However it didnt seem to work. The boiler didnt kick in when it should have done

Any ideas?

 

[bernardgreen]

Hi,
I connected red to 1 (common) and yellow to 3 (call for heat) and isolated the blue wire. However it didnt seem to work. The boiler didnt kick in when it should have done ?

Obviously you need to ensure the timing is set and the temperature is set high enough to require the boiler to come on.

Had you connected the neutral to the new thermostat before asking fot advice, if so then the live and neutral will have been shorted and the fuse in the boiler will have almost certainly blown

Check the fuse in the isolator switch for the boiler.

 

[DIY_Guy]

Hi,

I did connect the blue wire to the new thermostat and the fuse did blow. I subsequently replaced the fuse and connected the correct wires, i.e. red to common and yellow to call for heat. Timer was set to constant and temperature is set high enough to require the boiler to come on but for some reason it still didnt work. Maybe a faulty thermostat?

The boiler is a Baxi condensing bioler. Has only fitted about 12 months ago so guess will be compatible with a digital thermostat?

 

[bernardgreen]

There is also a fuse in the boiler on the PCB ( I think, depends on the model ) and that will have blown as well.

It is not the same type as fits a plug so you need someone to change it for you and check the PCB for damaged tracks.

 

[RF Lighting]

I did connect the blue wire to the new thermostat and the fuse did blow..............Maybe a faulty thermostat?

Probably is now

Try connect the red and yellow together in a strip connector, and see if the boiler runs.

If it does then the new stat is toast. You might have welded the contacts in the N/O position

 

[DIY_Guy]

Hi,

I did change a small 2amp fuse in the PCB and boiler lights re-appeared

I have also connected the red and yellow together and the bioler did run! so guess the thermostat is knackered. Any guess i know where the wires go now so should be ok for when i get a new one.

Bacially red to common and yellow to call for heat. Isolate blue as its not required?

 

[RF Lighting]

Yep thats it.

Have you retried the stat since you replaced the PCB fuse?

 

[DIY_Guy]

Yes tried the stat after replacing the PCB fuse but still no joy. Will try it again tomorrow just in case

Thanks to all those that responded

Regaeds

 

[steve1811uk]

I've got the same room stat myself. Try changing the temperature setting on the stat by pressing + and -. Each time the flame symbol on the stat display goes on or off you should hear a click as the internal relay in the stat changes over. If there is no click then the relay contacts are welded or the batteries are too low to operate the relay. Steve.

 

[karatedragon]

I replaced my old Honeywell knob thermostat (14 years old) with a Honeywell CM907 chronotherm room stat.

It seems this model is really easy to fit as you need just 2 wires.

Mine worked straight off no problem and took about 7 mins to do

 

[DIY_Guy]

Hi all,

I connected the red wire to common and yellow wire to call for heat. However, before i even put batteries in the thermostat the boiler fired up?

I noticed that the red wire has power going through it but so has the yellow. Is this normal?

 

[steve1811uk]

Put the batteries in and operate the + and - to switch the internal relay on and off. The relay can only operate with the batteries in. Also a latching relay is used (to save on battery power). If the relay is in the closed position, call for heat, then it cannot open again until you put the batteries in. If you are worried about causing further damage why not operate the thermostat with the boiler wires disconnected? You should hear the relay clicking on and off as the flame symbol goes on and off. The boiler wires do not actually provide power to stat. The Digistat 3 gets all its operating power from the 2 x 1.5v batteries. Steve.

PS. My boiler (Glowworm 38 CXi) has low voltage control for heat demand. Maybe yours has that option too. That means that I do not take high voltage (240V) to the thermostat at all. I just wire from the low voltage control of the boiler to the stat. That's a much safer way and less chance of the relay contacts getting stuck due to arcing contacts.