Convert Danfoss RMT230 Room Thermostate to Honeywell CM907

[simonjrichardson]

Hi

I have purchased for my mum a Honeywell CM907 to replace her RMT230 Danfoss thermostate to give her more control over heating coming on and off. I have installed an CM907 before to replace an RMT230, but when I did it at my house, I only had a two wire installation to convert so it was easy. At her house, she has a three wire installation. What should I do with her neutral wire ? Do I just safely isolate it ? I'm a bit unclear on what the neutral is doing for her boiler. Should it be a simple case of replacing her Danfoss with the Honeywell ? many thanks Simon

 

[flameport]

The neutral wire isn't required. The thermostat is just a switch.
The neutral is only used on thermostats with a built in neon indicator, or a heating resistor (or both)

 

[simonjrichardson]

thanks flameport ! fast reply !

that seems easy enough then.

Can you think of any gotchas I might experience ? The boiler was newly installed (replaced a 20 year old one) about 4 years ago - Its not been hugely reliable for her, it broke down again today because the condensor had blocked/frozen in the cold weather. boiling water on the outside pipe fixed that.

Simon

 

[333rocky333]

note the terminals and colours before removing.

Do not assume blue or black IS the neutral.

Especially at stats.

 

[simonjrichardson]

i made a note of the existing terminals on the RMT230 last time I was at her house by taking the RMT230 off the wall after cutting all of the power at the ICD box for the whole house (i don't take chances with electricity !)
This is what I noted was connected.

4 = Blue Wire (Neutral)
1 = Brown Wire (COM)
2 = Black Wire (ON)
3 = Empty terminal (OFF)

an earth wire was hanging free inside the wall

The boiler is an Ideal Mexico.

Based on what you've said and what I'd summised.

I connect Brown Wire to terminal A on the new 907 thermostat

I connect Black Wire to terminal B on the new 907 thermostat

I isolate Blue wire with a plastic block

I leave the earth wire as it is (disconnected)

Does this sound right ?

 

[Taylortwocities]

Yes that's right.

I assume the old neutral conductor is a grey wire, sleeved in blue?

 

[simonjrichardson]

I'm not sure what colour the original cable was, all I remember was that the sleeve cable colour was blue. I can check this when i change it next weekend

 

[simonjrichardson]

I don't suppose it will make any difference that the boiler is a condensor boiler rather than a Combi boiler will it ?

 

[londonboy]

I don't suppose it will make any difference that the boiler is a condensor boiler rather than a Combi boiler will it ?

Is it a condensing combi?

BTW re-run the condense in 32/40mm waste with a better fall and it won't freeze up

 

[simonjrichardson]

yes, its a condensing one. the condensor froze up over the weekend ! boiling water had to be poured on the pipe outside.

 

[simonjrichardson]

this is the boiler

http://www.idealboilers.com/mexico_he_details.html

 

[londonboy]

Yes it doesn't matter, the wiring connections are virtually the same on all combis. Both condensing and non condensing.

That pipe will keep freezing up, can you rerun it internally?
Or do as I said and use 32/40 waste pipe?

 

[londonboy]

Thats not a combi boiler.
Thats a condensing heat only boiler.

I guess theres an airing cupboard with tank, valves + pump in?

The thermostat will still work correctly though.

 

[simonjrichardson]

ah, sorry, I'm not very clued up on boilers yes, there is an airing cupboard upstairs with a tank in it yes. it has various bits attached to it yes. great, thank you for clearing that up. My mother had an electrician round today to do something else, and he said the Honeywell thermostat wouldn't work to replace the Danfoss...I thought he was wrong...many thanks for confirming that. cheers simon

 

[Taylortwocities]

he said the Honeywell thermostat wouldn't work to replace the Danfoss...I thought he was wrong...many thanks for confirming that. cheers simon

Well he's talking bovine scatology