Replacing Honeywell CM921

[Clairebear]

Hi,

I need to replace our Honeywell CM921 wireless thermostat. The screen has been failing for the last few years, it's about 13yrs old. I tried removing the screen and heating it over a toaster ala Youtube video I saw but it didn't help 🙂

I'm looking at some second hand/nearly new ones on a local site. I have found a T4R reasonable, just the thermostat, not the receiver, which would save a bit of money but I can't find out if this new thermostat can communicate with the old receiver of the CM921? I can definetly wire in a new one if I have to bit would just be cheaper if I didn't need to get both.

The boiler is a Vaillant Ecotec Plus.

Thank you!!

 

[ShaunCorbs]

No need the receiver as well

 

[Deleted member 120897]

If it’s the Honeywell home unlikely, if it’s the bdr91 perhaps it may? Honeywell

 

[Chuck]

"The T4R has a new design of receiver. The T4R cannot connect to the BDR91 receiver, as now it uses an encryption algorithm. This is also applicable for the T3R thermostat. The same principle applies for the CM927: it cannot connect to the T4R's receiver."

getconnected.honeywell.comensupport

 

[Clairebear]

Thank you, that's just the information I couldn't find any where. I def don't want a smart thermostat, would the T4R be a good choice?

I would look again on the second hand sites for one with the receiver.

 

[Clairebear]

Also I'm assuling the same cable coming out of the boiler to the thermostat can be reused? It was all ready a wireless thermostat. Not sure I would be willing to replace the cable myself, thanks!

 

[ShaunCorbs]

Combi pack 4 around 50 plus the vat

And yes can re use the cable

 

[Deleted member 120897]

"The T4R has a new design of receiver. The T4R cannot connect to the BDR91 receiver, as now it uses an encryption algorithm. This is also applicable for the T3R thermostat. The same principle applies for the CM927: it cannot connect to the T4R's receiver."

getconnected.honeywell.comensupport

Is this a recent thing? When we were getting the T3R thermostats they had to revert back to bdr91’s because they couldn’t get hold of something for the home ones.

 

[Chuck]

If the OP wants to keep using their BDR91, Honeywell spun off the CM700 and CM900 line into a separate company 'Resideo (Honeywell Home)', who sell the replacements that bind to the BDR91.

Like @Undertrained, I seem to remember the T3R binding to the BDR91, I have a feeling that there is an installer parameter (14A ?) that needs to be changed from the factory default for binding to the BDR91 to work. I don't have one to hand to check, however, so someone else will need to confirm this before it can be relied upon.

 

[Deleted member 120897]

I have a feeling that there is an installer parameter (14A ?) that needs to be changed from the factory default for binding to the BDR91 to work. I don't have one to hand to check, however, so someone else will need to confirm this before it can be relied upon.

Yep, here mentions rebinding.