Wiring a Hoeywell CM927 to a Worcester 28i Junior Boiler

clbg07651 · 17 Dec 2009

Dear All,

Please can you give me some advice on replacing my current honeywell non digital thermostat with a honeywell CM927.

I've read over some similar threads on here but I am still a little confused.
Currently I have 3 wires running to the thermostat. I'm hoping not to have to do any additional wiring on the boiler. From reading other threads I believe i can spur the 1 live wire into 2?

Please see below a pic of my current thermostat wiring. Currently I have a blue wire to terminal 2, black wire to terminal 3 and a brown wire to terminal 1. From looking at the thermostat cabling diagram I have 6 terminals N L L A B C

Untitled

clbg07651
17 Dec 2009
1

Your help will be appreciated.

Many Thanks

Chris

clbg07651 · 18 Dec 2009

I'm going to try and wire it tonight. Any help anyone please.

Thanks

Chris

D_Hailsham · 18 Dec 2009

Wire as follows:

[code:1]
Old - New
1 - L
2 - N
3 - B
[/code:1]
Also inset a short link between L and A on the new stat.

If you have an existing timer for the heating you should either set the heating to continuous or move the wire connected to CH ON terminal to the Live terminal.

clbg07651 · 18 Dec 2009

Thanks for your reply. That's made it seem a really simple job. The boiler has got a built in timer so should I set the progs to he default and switch the boiler to the always on option?

Many thanks again for your help

Chris

D_Hailsham · 18 Dec 2009

clbg07651 said:
The boiler has got a built in timer so should I set the progs to he default and switch the boiler to the always on option?

Are you talking about setting the built in timer progs to default?

The boiler should be set to the always on option. If you do that the built in progs are not used.

clbg07651 · 18 Dec 2009

Yes I was refering to the timer which is part of the boiler and setting the multiple time settings to 0:00 to 0:00 which I believe skips that option. As you mentioned setting the boiler to the perm on position over rides those options anyway.

So in brief, fit the current cables to the terminals you previously mentioned and with a 2 inch piece of cable connect the 2 terminals you mentioned.

Many Thanks

D_Hailsham · 19 Dec 2009

clbg07651 said:
So in brief, fit the current cables to the terminals you previously mentioned and with a 2 inch piece of cable connect the 2 terminals you mentioned.

Correct.

clbg07651 · 20 Dec 2009

Just wanted to post a quick update to say that the new thermostat is all fitted and working great. Big thanks to D_Hailsham for his excellent advice which made the fitting so simple.

I fittted this as we have just had a first child, now 3 months old in her own room and wanted to regulate the temperature for her during the night. I have also looked at the HR80 radiator control valves but am not sure if it's worth the investment?

Pic of the fitted thermostat reciever. Ignore the dodgy screws it's what the original plumber used and they fitted so I thought what the heck.

Untitled

clbg07651
20 Dec 2009
1

Thanks again for your sound advice.

P.S. I was ok to use a solid core cable for the link?

D_Hailsham · 20 Dec 2009

clbg07651 said:
I fittted this as we have just had a first child, now 3 months old in her own room and wanted to regulate the temperature for her during the night. I have also looked at the HR80 radiator control valves but am not sure if it's worth the investment?

It's more important that a baby does not get too hot as they are unable to regulate their temperature. The room temperature should not be over 18°C.

HR80 are very expensive toys.

P.S. I was ok to use a solid core cable for the link?

Yes.

clbg07651 · 20 Dec 2009

That is the plan to have the wireless thermostat to keep her room below 18c nearly impossible with the hall thermostat. I've got so many thermometers around the house it's crazy.

D_Hailsham · 20 Dec 2009

clbg07651 said:
That is the plan to have the wireless thermostat to keep her room below 18c nearly impossible with the hall thermostat. I've got so many thermometers around the house it's crazy.

Why not fit a thermostatic valve onto the radiator in your daughter's bedroom? You could then set it to keep the temperature to 18C. The wireless stat could then replace the hall stat and control the temperature in the rest of the house.

clbg07651 · 21 Dec 2009

Can you recommend a make and model for the type of valve you mentioned? Roughly how much will one cost and are they easy to fit?

Many thanks for your advice

D_Hailsham · 21 Dec 2009

clbg07651 said:
Can you recommend a make and model for the type of valve you mentioned? Roughly how much will one cost and are they easy to fit?

Drayton TRV4 are probably the best. £20 from Screwfix etc but you can often get brand new ones on Ebay for £10-15.

Installation is easy, but you have to drain down the system to change the valve.

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Wiring a Hoeywell CM927 to a Worcester 28i Junior Boiler

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