Alternative to LCD programmer

[jasoninhants]

Hi, hope someone can help. We currently have a Honeywell CM901 in our conservatory to control underfloor heating in there. However, the LCD display has failed on this and a previous unit, presumably due to the cold. I've tried rejuvenating the LCD display (via YouTube techniques) which gives a temporary fix but I'm looking for a longer-term solution.

I don't really need a thermostat in there and would be happy with a simple timer - however, one without an LCD display. Could someone recommend a suitable mechanical timer that could be wired into the existing circuit in place of the CM901?

Thanks in advance.

 

[oilhead]

Screwfix Greenbrook T100A-SCR will fit your bill

 

[jasoninhants]

So, recommended device purchased but hoping for further advice please. The Honeywell CM901 I've removed had mains L coming to terminal A and mains N to terminal B. They were the only wires coming through the wall to the socket.

The Greenbrook is designed to power a separate device and suggests wiring mains N and device N into terminal 1, mains L into terminal 3 and the device L to terminal 4 (switched live). However, I don't have a third wire. For now, I've put mains L and N into 1 and 3 respectively and the timer has power - but with nothing to put into terminal 4 (switched live) I'm not sure how I can get the underfloor heating to come on. It currently doesn't, even when I switch the timer to override/on.

Should I loop switched L from terminal 4 into mains L in terminal 3 - or is that a bad idea?!

Thanks in advance for any guidance. I appreciate I may need to fork out for an electrician to look at this.

 

[polesapart]

..... and mains N to terminal B.

You may well have a blue wire there (which should have oversleeved/tagged) but no way is that a neutral.

On temperature fall ("call for heat") this will have the same voltage as terminal A.

 

[RandomGrinch]

The Honeywell CM901 I've removed had mains L coming to terminal A and mains N to terminal B.

Your CM901 was battery operated.
If the wires were connected to A and B, they were not a Live and a Neutral (despite the wire colours) - they were a Live and a switched live.

You are missing a neutral to power the Greenbrook. The return to the UFH, is acting as a false neutral, hence it is appearing to be powered at the moment.

If you can post a picture of the wiring behind the controller, we may be able to advise whether it's possible to provide a neutral, or if it may be simpler to find another battery operated timer.

 

[jasoninhants]

Ah, I see - this does make sense as I have since tested the voltage coming to the socket and only around 30v. I will aim to post a picture in the next few days but as you suggest, a battery-powered timer (without LCD) may be a better bet. Thanks so much to both of you for taking time to explain.

 

[RandomGrinch]

this does make sense as I have since tested the voltage coming to the socket and only around 30v.

Was this measured between the brown and blue wires, or was that with one probe on an earth?

 

[jasoninhants]

Between brown and blue

 

[RandomGrinch]

Between brown and blue

Then that's fine. Measured between earth, you would probably have seen around 230V on the meter.

 

[ianmcd]

Ah, I see - this does make sense as I have since tested the voltage coming to the socket and only around 30v.

Between brown and blue

Be very carefull, your existing has volt free switching and if you put mains voltage in there , it may be a very expensive mistake, you need to see where the existing wires in A&B are connected at the boiler , which boiler do you have ?

 

[jasoninhants]

Hi, thanks again for taking time to consider this. I plan to source a replacement programmer that is battery operated, although I'll have a go at rejuvenating the LCD screen on the CM901 first. Thanks again!