Wiring Difficulties Replacing Very Early Drayton Digistat

[transam]

Must admit I looked at this post & I lost the will to live I reckon the O.P is deliberately winding people up , that is & was the entire purpose of his post ??

 

[picasso]

I have just skimmed throught this thread and thought that d hailsham deserves a ******* medal for having the patience, capvermel deserves to see the ID TEN T code come up on his room stat.

 

[Capvermell]

To further update the saga due to both what had previously happened (i.e. frying the old Drayton Digistat with Black wire attached to Dem and red to Live) and due to d_hailsham's advice I was reasonably convinced that red to A and Blue to B was the correct solution but in the end a local electrician was called in to check things out before taking the risk. The fact that as he lived only a mile away his charge was only £35 (no VAT required for cash payment it seemed) further encouraged this course of action as did the fact that the CM907 could not be replaced for a number of days if fried by a wrong connection.

The electrician checked out continuity through to the boiler and opened various switch panels and the main electrical wiring run panel at the boiler end and confirmed that the blue wire led back to the pump. The black wire at the room stat on the other hand was definitely a neutral.

So the CM907 was then pressed in to service and all seemed to be well with Red attached to A and Blue to B with the CM907 running the central heating pump when the room temp was below the set temp. The stat was then further programmed with a sensible temp range at the six switching points on each day of the week.

However the one fly now remaining in the ointment is that if the boiler controller is run in HW only mode (with HW set to Twice) and CH set to Off it appears that during the periods of HW only heating that if the CM907's set temp is above the current room temp that the pump also runs and heats the radiator during the periods while the boiler is supposedly only running only in HW mode.

My relative swears blind that with the old Drayton Digistat in place that with the HW only circuit switched on and the CH circuit at Off on the Drayton Tempus 7 the radiators never ever heated up at all and that only when the CH circuit was switched on would the radiators circuit operate at all.

Yet as there is no valve for the downstairs heating circuit (it was physically removed from the pipework 15 or more years ago) and as the upstairs valve was disconnected from the timeclock that controlled it in the open position five or so years ago (when the valve failed) to my knowledge the only controlling factor in the whole heating setup is whether power to the boiler is on (determined by the Tempus 7 programmer times) and whether the heating pump runs (determined by the CM907 room stat and whether it is up to the set temp or not). So as far as I can see in this configuration the radiators always would have heated up during the time of Hot Water heating if the room stat temp was below the set temp, even with the programmer for the CH was set to Off. The only way this would not have happened previously would have been if the heating circuit pump did not run when the programmer was only in HW mode.

Personally I am somewhat inclined to believe that my mother is imagining things and that because it is June she is now checking and noticing that the radiators are also being heated on a summer's day when the HW is heated, even though it is not by very much. The other thing is that she had set a four hour period from 6am to 10am for the HW only heating whereas normally the gravity fed water tank would only need an hour of boiler heating to get up to temp.

If she insists this is happening and does not want it to happen I can see various ways round the problem if she insists on still running in HW only mode on the Tempus 7 in the mid summer month. These include both setting the heating hours of the water to say 6am to 7am before the CM907 temp increases set temp from 18C to 21C and disabling Optimum Start since Optimum Start has the consequence of not being able to be sure when the circulation pump will start operating for the day.

To my mind she is simply looking to find fault as all that was actually happening was that the central heating was being heated to a temp that it was set to be at by the CM907 but could she be right that the radiators never ever heated before when the Drayton Tempus 7 was set to HW mode regardless of the Room Stat setting in relation to the room temp and if so what could have been changed by a simple room stat substitution to bring this about?

 

[D_Hailsham]

To further update the saga due to both what had previously happened (i.e. frying the old Drayton Digistat with Black wire attached to Dem and red to Live) and due to d_hailsham's advice I was reasonably convinced that red to A and Blue to B was the correct solution but in the end a local electrician was called in to check things out before taking the risk. The fact that as he lived only a mile away his charge was only £35 (no VAT required for cash payment it seemed) further encouraged this course of action as did the fact that the CM907 could not be replaced for a number of days if fried by a wrong connection.

The electrician checked out continuity through to the boiler and opened various switch panels and the main electrical wiring run panel at the boiler end and confirmed that the blue wire led back to the pump. The black wire at the room stat on the other hand was definitely a neutral.

Where do I send my bill to??

So the CM907 was then pressed in to service and all seemed to be well with Red attached to A and Blue to B with the CM907 running the central heating pump when the room temp was below the set temp. The stat was then further programmed with a sensible temp range at the six switching points on each day of the week.

You don't have to use all six points every day, particularly if the house is occupied all the day. You can disable setting points.

However the one fly now remaining in the ointment is that if the boiler controller is run in HW only mode (with HW set to Twice) and CH set to Off it appears that during the periods of HW only heating that if the CM907's set temp is above the current room temp that the pump also runs and heats the radiator during the periods while the boiler is supposedly only running only in HW mode.

Sounds as if the CM907 is not getting its supply from the boiler controller (Tempus 7?) but directly from a permanent 230v supply. The easiest way to prevent the heating coming on in the summer is to set the slide switch of the CM907 to OFF. The heating will then only come on if the temperature drops below 5degC.


[/quote]The other thing is that she had set a four hour period from 6am to 10am for the HW only heating whereas normally the gravity fed water tank would only need an hour of boiler heating to get up to temp.[/quote]
As I said previously, the main problem with your system is that the HW has to be on for the CH to work. So, a four hour period would be perfectly sensible in the winter, but not in the summer.

The HW times should be set to, say 1 hour in the summer.

If you turn the CM907 OFF, as suggested above, you don't have to worry about Optimum Start.

These include both setting the heating hours of the water to say 6am to 7am before the CM907 temp increases set temp from 18C to 21C and disabling Optimum Start since Optimum Start has the consequence of not being able to be sure when the circulation pump will start operating for the day.

If you think about it, this will not work. If the HW goes off at 7am then so does the CH.

 

[Capvermell]

Where do I send my bill to??

I'm quite sure that unlike some other forum members (who only seem to enjoy pouncing on the incompetent non professionally trained newbie and vilifying their efforts) you clearly enjoy helping the initially incompetent amateur to learn and increase their meagre skill set. So that perhaps may brings its own reward.

Also the electrician who sets foot in someone's house is on risk if something major goes wrong due to their intervention whereas the same is not true of the helpful forum member.

You don't have to use all six points every day, particularly if the house is occupied all the day. You can disable setting points.

Yes I did read that in the manual but it actually seemed quite easy to use them all up, especially given my mum's requirement that the temp should go up again just before she goes to bed then go down an hour after she has usually gone to sleep and then go up again in the morning just before she gets out of bed.

Sounds as if the CM907 is not getting its supply from the boiler controller (Tempus 7?) but directly from a permanent 230v supply.

There is a second red wire that comes in to the room stat point but that I had taped out when I removed the Satchwell stat and replaced it with the Drayton Digistat 15 years ago. I assume that is therefore probably the correct switched live red wire coming from the Tempus 7 programmer. Something to be tried perhaps when I am staying for a day or two but my mother goes out for a number of hours.

The easiest way to prevent the heating coming on in the summer is to set the slide switch of the CM907 to OFF. The heating will then only come on if the temperature drops below 5degC.

Except that out here in the countryside some heating is often necessary in the summer months between about 9pm and midnight. I had already changed the ludicrously low 5C factory setting for Off on the CM907 (which would almost certainly see pipes in the loft or on cold outside walls freeze in really bad weather) to 10C in Installer mode.

The only real solution is to attach the correct switched live so that the pump does not run if the boiler is in HW only mode.

If the HW goes off at 7am then so does the CH.

Correct but up to 7am the room stat temp setting will be say 18C so in the summer the CH will not come on and heat the rads while the hot water is heating. Then when the set CH temp changes to 21C the programmer will have switched off HW only so the central heating rads will not end up being heated as they are at present.

 

[PEDANTICVINDICTIVEMAN]

A whole £35.00, jeez as much as that, bloody rip off merchant........

 

[Capvermell]

A whole £35.00, jeez as much as that, bloody rip off merchant........

No £35 was a fair price. Another guy wanted £50. He didn't get the job. The guy I used had his own website and also seemed to have one of the electrical body training qualifications.

However his main job seemed to be wiring whole new circuits in house extensions or new homes so the fact that digital room stats were now switched by battery rather than mains current did seem to be something he was not acquainted with until I explained that this was how it was switched.

 

[Boilerman2]

Sounds like it would be £100 well spent!! (just try not to upset him or her tho!)