Honeywell CM900 Install

eeiecoe

Hi,

I am trying to install a Honeywell CM900 wired thermostat but running into problems.

There are 3 wires -

1) Brown one (Live)
2) Blue
3) Brown two (separate with a grey case around it)

Here is the wiring diagram of the CM900:

http://i88.photobucket.com/albums/k182/honeymonster79/honeywell.jpg

I have wired the "Brown Live" going into C
I have wired the "Blue" going into B
I have wired the "Brown two" going into A

But this combination keeps the boiler OFF when the termostat is saying it should be ON. If I reverse the "Brown Live" and the "Brown two" the fuse on the fuse board triggers.

fishdog

Connect one (either) brown in to A the other brown into C and the blue (if there is just one) to nothing. Ensure the blue makes contact with nothing. The stat may require an earth.

To be sure I would really have to see it, but the chances are that information will do the trick!
If you are not 100% happy get a qualified electrician to look at it.

eeiecoe

Thanks for your reply.

Ok I just did that (disconnected the blue) and put the brown permanent live into A and the other brown into C. The fuse no longer triggers.

However the unit does not appear to be controlling the boiler. The boiler is firing up and down randomly like its on a termostat of its own. If I turn off the therm unit the boiler continues to work away regardless....very weird

fishdog

The boiler is firing up and down randomly like its on a termostat of its own

This stat I would assume is turning the boiler on and off. You may be just hovering around the set point.

If I turn off the therm unit the boiler continues to work away regardless....very weird

I assume what is happening is that you are turning the stat to a set point (temerature) that is higher than the bolier can ever reach so the boiler simply does not go off.

Phibsboro

Just as a matter of interest, I am looking at installing a similar yoke and asked in the DIY forum re general approach. The reply was that there should be a "no volt" option to wire the thermo directly into the timer circuit on the boiler, as opposed to having the thermo turned on and off the boiler at the mains. The reply said that the boiler should continue to have power after the temperature is reached to enable the pump to continue to move hot water around the system. And indeed, the particular model I was looking at (the digistat 3) does have a no volt option, although im not sure how to wire it into my boiler. But then those CM900 diagrams do seem to be based on turning on and off the mains. Am I missing something? Any further explanation or information would be gratefully received.

C

Phibsboro

just to correct my previous post, it was actually a different model honeywell i referenced in my DIY post (i've looking at both it and the digistat). That thread has further explanations on it that I need to digest so I'd say ignore my point above.

Thanks,
c

fishdog

Just as a matter of interest, I am looking at installing a similar yoke and asked in the DIY forum re general approach. The reply was that there should be a "no volt" option to wire the thermo directly into the timer circuit on the boiler, as opposed to having the thermo turned on and off the boiler at the mains. The reply said that the boiler should continue to have power after the temperature is reached to enable the pump to continue to move hot water around the system. And indeed, the particular model I was looking at (the digistat 3) does have a no volt option, although im not sure how to wire it into my boiler.

This is all correct.

But then those CM900 diagrams do seem to be based on turning on and off the mains

This is not really correct. Think of it like this: A stat is just a type of switch. If it can switch 230 volts (mains) it can switch 12 or 24 volts.

goodguy001

Hi,


Im installing the honeywell CM900.

I have 3 wires comming out of the wall and 1 earth. All 4 were connected to my old thermostat SUNVIC TLM 2253.

Ok i know i dont need the earth, so I have the 3 wires:

brown = LIVE (connected to 3 on sunvic)
black(with brown sheath) = NEUTRAL? (connected to 1 on sunvic)
grey(with blue sheath) = NEUTRAL? (connected to 4 on sunvic)

SUNVIC TLM 2253 WIRING:
https://www.uk420.com/boards/uploads/monthly_09_2008/post-26762-1221828368.jpg

CM900 WIRING:
http://i88.photobucket.com/albums/k182/honeymonster79/honeywell.jpg

I have connected

brown to 'A'
black(with brown sheath) to 'B'

But, do i connect grey(with blue sheath) to 'C'?

well i left the grey(with blue sheath) disconnected. The heating works great, but i cant turn my water completely off at the combi boiler like before.

Is the 'C' connection on the CM900 for a second neutral? i.e my grey(with blue sheath)


If anyone can shed some light my way, id very much appreciate it.

Thanks