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I am trying to update an original wired Mk1 Drayton Digistat that I fitted myself as a replacement for an analogue Satchwell (or I think it could possibly have been a Honeywell) room stat in either 1993 or 1996 with a HoneyWell Chronthem CM907 Roomstat. This is the very earliest LCD digital stat from Drayton before they had several models in their digital stat range. The boiler is an oil fired boiler on an old style gravity feed system where the hot water circuit is always also heated up when the central heating is running although the hot water circuit can be heated up with the central heating circuit switched off.
In any event when I fitted the very old Drayton Digistat 15 or more years ago I was faced with a 5 wire set up on the back of the previous room stat with red, black, blue, green and yellow wires. This is because the room stat (previously I think a Satchwell) originally controlled a driven motorised valve for the downstairs heating circuit while the upstairs circuit originally had a motorised driven valve controlled by a timeclock. However the downstairs valve had failed some years earlier and the system was then modified so that the room stat now only switched on or off the heating pump. More recently the upstairs mechanical Satchwell time clock became intolerably noisy and rather than being replaced was simply disconnected by the boiler servicing engineer and the upstairs circuit valve left permanently open.
In the mid 1990s when I removed the Satchwell stat and fitted the Drayton Digistat I blanked off the green and yellow wires and connected the remaining three wires (red, black and blue) to the Drayton Digistat. However when I came to try to change the stat today the wiring to the four terminals was shielded with black electrical tape and I may not have accurately noted down which wire was connected to which terminal but definitely the Red wire was connected to Terminal 1/Live and I thought the Black wire was connected to terminal 3/Sat and the blue wire to terminal 4/N but possibly the Black wire was connected to Terminal 2/Dem but a wire was definitely connected to terminal 4/Neutral and I thought it was Blue unless the Black and Blue were the other way round.....
Trying to cut a long story short after reading up on this forum about the dangers of wrongly connecting the Neutral wire to the new CM907 and blowing it up I became scared about the risk of destroying it and so decided to put the old Drayton Digistat back for now. I hasten to add that whenever I was working on the wiring on the back of the stat I always turned off the mains supply since I acknowledge that I am not a qualified electrician, even though in theory a room stat's wiring is not much more complicated than a wall light switch.
Anyhow putting the wiring back on the Drayton Digistat I consistently kept the red wire on Terminal 1/Live but as I was having no luck making the room stat switch on or off the heating pump tried a number of combinations of the blue and black wires on terminals 2 (Dem), 3 (Sat) and 4(N). A couple of these combinations blew the 3 Amp fuse of the wall switch controlling the power to the central heating programmer and heating pump next to the boiler in the kitchen (the room stat is in the living room) and other combinations did not blow the fuse and the programmer functioned as normal but throughout the boiler would now only operate in response to demand from the hot water circuit and after the boiler had reached temperature turning up the Digistat to a level that should have caused the central heating pump to operate and make the boiler fire up failed to do so. The Digistat made the usual on/off clicks but the pump belligerently refused to cut in and then make the boiler fire as the water temperature in the boiler dropped.
Finally after trying various three wire combinations (always keeping the red wire on L but with Blue and Black on a variety of 2, 3 and 4 ) I made the probably rash decision to connect just the red wire to 1 and the black wire to terminal 3/Sat. When I turned the mains back on after this there was a nasty pop from the Digistat and a burning smell and its clear that I have fried it as all it now shows is CHECK BATTERY and replacing the battery does not help.
I accept that I may well need to get in a professional central heating engineer or electrician to finish the job but can anyone clarify whether the fact that a combination of the red wire to terminal 1/Live and just the Black wire to 3/Sat burned out the digistat possibly suggests that the Black wire is in fact the Neutral wire or is the fact that I attached the black wire to terminal 3 without also having the Blue Neutral wire attached to terminal 4 responsible for the burn out incident? I had previously had the blue and black wires attached to terminals 3 and 4 together in both possible orders and neither of these combinations burned out the Digistat.
If I go to B&Q or another DIY shed I can clearly buy some sort of mains wiring tester but other than establishing that the red wire is the live wire should I also be able to definitely establish which of the black and blue wires is Neutral and should therefore not be used with the CM907? I assume that the green and yellow wires I taped out 15 years ago are not needed as the old Drayton Digistat has been using just the red, blue and black wires to operate for all these years with no problems other than a battery change every couple of years.
I should add this room stat is on my 75 year old widowed mother's heating and hot water system so I am now severely in the dog house for screwing it up when all I was trying to do was to make the system more efficient and less hassle as the very first Drayton Digistat is a real pain because to turn the temperature down two degrees you have to cycle all the way up the high 80Fs and then roll back down to the 40Fs and all the way round just to make that small adjustment.
I know that there will inevitably be plenty of you on here now wanting to deride me for taking on this job when I am not a qualified electrician but all I can say is that I did manage to fit the old Digistat ok myself and I do take sensible precautions such as switching off the mains before i work on the wiring connected to the room stat.
If anyone can help and particularly comment on why they think attaching just the red wire to Terminal 1/L and the Black wire to Terminal 3/Sat blew it up then it would be very much appreciated.
In any event when I fitted the very old Drayton Digistat 15 or more years ago I was faced with a 5 wire set up on the back of the previous room stat with red, black, blue, green and yellow wires. This is because the room stat (previously I think a Satchwell) originally controlled a driven motorised valve for the downstairs heating circuit while the upstairs circuit originally had a motorised driven valve controlled by a timeclock. However the downstairs valve had failed some years earlier and the system was then modified so that the room stat now only switched on or off the heating pump. More recently the upstairs mechanical Satchwell time clock became intolerably noisy and rather than being replaced was simply disconnected by the boiler servicing engineer and the upstairs circuit valve left permanently open.
In the mid 1990s when I removed the Satchwell stat and fitted the Drayton Digistat I blanked off the green and yellow wires and connected the remaining three wires (red, black and blue) to the Drayton Digistat. However when I came to try to change the stat today the wiring to the four terminals was shielded with black electrical tape and I may not have accurately noted down which wire was connected to which terminal but definitely the Red wire was connected to Terminal 1/Live and I thought the Black wire was connected to terminal 3/Sat and the blue wire to terminal 4/N but possibly the Black wire was connected to Terminal 2/Dem but a wire was definitely connected to terminal 4/Neutral and I thought it was Blue unless the Black and Blue were the other way round.....
Trying to cut a long story short after reading up on this forum about the dangers of wrongly connecting the Neutral wire to the new CM907 and blowing it up I became scared about the risk of destroying it and so decided to put the old Drayton Digistat back for now. I hasten to add that whenever I was working on the wiring on the back of the stat I always turned off the mains supply since I acknowledge that I am not a qualified electrician, even though in theory a room stat's wiring is not much more complicated than a wall light switch.
Anyhow putting the wiring back on the Drayton Digistat I consistently kept the red wire on Terminal 1/Live but as I was having no luck making the room stat switch on or off the heating pump tried a number of combinations of the blue and black wires on terminals 2 (Dem), 3 (Sat) and 4(N). A couple of these combinations blew the 3 Amp fuse of the wall switch controlling the power to the central heating programmer and heating pump next to the boiler in the kitchen (the room stat is in the living room) and other combinations did not blow the fuse and the programmer functioned as normal but throughout the boiler would now only operate in response to demand from the hot water circuit and after the boiler had reached temperature turning up the Digistat to a level that should have caused the central heating pump to operate and make the boiler fire up failed to do so. The Digistat made the usual on/off clicks but the pump belligerently refused to cut in and then make the boiler fire as the water temperature in the boiler dropped.
Finally after trying various three wire combinations (always keeping the red wire on L but with Blue and Black on a variety of 2, 3 and 4 ) I made the probably rash decision to connect just the red wire to 1 and the black wire to terminal 3/Sat. When I turned the mains back on after this there was a nasty pop from the Digistat and a burning smell and its clear that I have fried it as all it now shows is CHECK BATTERY and replacing the battery does not help.
I accept that I may well need to get in a professional central heating engineer or electrician to finish the job but can anyone clarify whether the fact that a combination of the red wire to terminal 1/Live and just the Black wire to 3/Sat burned out the digistat possibly suggests that the Black wire is in fact the Neutral wire or is the fact that I attached the black wire to terminal 3 without also having the Blue Neutral wire attached to terminal 4 responsible for the burn out incident? I had previously had the blue and black wires attached to terminals 3 and 4 together in both possible orders and neither of these combinations burned out the Digistat.
If I go to B&Q or another DIY shed I can clearly buy some sort of mains wiring tester but other than establishing that the red wire is the live wire should I also be able to definitely establish which of the black and blue wires is Neutral and should therefore not be used with the CM907? I assume that the green and yellow wires I taped out 15 years ago are not needed as the old Drayton Digistat has been using just the red, blue and black wires to operate for all these years with no problems other than a battery change every couple of years.
I should add this room stat is on my 75 year old widowed mother's heating and hot water system so I am now severely in the dog house for screwing it up when all I was trying to do was to make the system more efficient and less hassle as the very first Drayton Digistat is a real pain because to turn the temperature down two degrees you have to cycle all the way up the high 80Fs and then roll back down to the 40Fs and all the way round just to make that small adjustment.
I know that there will inevitably be plenty of you on here now wanting to deride me for taking on this job when I am not a qualified electrician but all I can say is that I did manage to fit the old Digistat ok myself and I do take sensible precautions such as switching off the mains before i work on the wiring connected to the room stat.
If anyone can help and particularly comment on why they think attaching just the red wire to Terminal 1/L and the Black wire to Terminal 3/Sat blew it up then it would be very much appreciated.
