baxi 105 e room thermostat

[leso54]

hello everybody,i have a baxi 105e combi boiler with a time control built in, iv'e been looking at a Honeywell CMT927 (CM927) Wireless Programmable Room Thermostat or something similar and wonder if it would be possible to use one of these with my boiler as i dont have a room thermostat fitted anywhere at the moment as all rooms have thermostatic radiator valves. Any thoughts on the matter would be gratefully accepted, many thanks in advance.

 

[Corgigrouch]

Yep, that'll work just fine, just remember to swap the TRV on the rad in the room where the roomstat is fitted with a normal wheel valve

 

[leso54]

Many thanks for the reply, hadn't thought about removing radiator valve, is it a major job to wire receiver unit into boiler or is it something a very competent diy'er could do, would i be right in assuming i can switch central heating on from where ever thermostatic sendr unit is as opposed to going to where boiler is ie upstairs if i want to override time controls?
many thanks again.

 

[D_Hailsham]

is it a major job to wire receiver unit into boiler or is it something a very competent diy'er could do,

The receiver needs a permanent 230vac supply from the same connection as the boilers supply (two wire only, no earth) to the L and N terminals to run the device.

It then requires a twin cable from the A and B terminals to the boiler terminals 1 and 2 (far end from the fuse). The link joining 1 and 2 must be removed.

If you wanted to, you could use a four core cable and take the supply from the boilers L and N terminals

It's diagram 4b in the installation manual

would i be right in assuming i can switch central heating on from where ever thermostatic sender unit is as opposed to going to where boiler is ie upstairs if i want to override time controls?
many thanks again.

Yes

 

[baxpoti]

[If you wanted to, you could use a four core cable and take the supply from the boilers L and N terminals

Although running a five core and terminating the cpc correctly at the roomstat would be correct.

 

[D_Hailsham]

[If you wanted to, you could use a four core cable and take the supply from the boilers L and N terminals

Although running a five core and terminating the cpc correctly at the roomstat would be correct.

I should, of course, have said a four core plus earth cable.

The CM927 receiver does not have an earth terminal and does not require one, so I don't see how the CPC can be terminated correctly. The earth core is redundant and can be cut off flush with the outer sheath at each end.

Using a three core plus earth and then using the earth wire as a current carrying wire is a a non-starter.

 

[leso54]

Thanks for your replies, i now know what i'm doing and have ordered the thermostat, glad i've found the forum, many thanks for your advice.