Centaurplus C27 to Honeywell Evohome Wiring

[somedudebob]

Hello. Im about 90% sure I know what Im doing here, Just looking for someone to check over before I dig in.

Im removing a Centaurplus C27 with stored hot water and fitting the Evohome setup that I had from my previous house. Old house was gas with on-demand hot water, so I have bought the hot water add on for this, Which leaves me wiring up 2 BDR91s in replacement of the old C27.

Im pretty sure its as simple as connecting the live and earth from the C27 to both BDR91s, then C27 1&2 go to the BDR91 for heat conections B&C, C27 3&4 to the BDR91 for hot water B&C and a link L to A on both BDRs

The honeywell system should then take care of the thermostat, however, there is a room thermostat that needs to be removed, and that part Im not sure of. I suppose I could set it on full and let the evohome do the job, but Id rather remove. Any tips? or anything I havent got right?

Thanks in advance!

 

[stem]

Your theory is along the right lines, however, regarding:

C27 1&2 go to the BDR91

Are there presently wires connected to the C27 terminals 1 & 2? A connection to terminal 1 is fairly common in the UK (but not always it depends on the type of system it's connected to), but it would be extremely unusual to have a connection to terminal 2, [CH Off]

 

[somedudebob]

Hi.. Thanks for the reply. The C27 thats in place at the minute is working to the extent where I can turn the heating and HW on and off, Just not set timers, (screen is dead)

Im loathed to remove it to check until Im sure what I am doing, as if it doesnt come back on, and the heating doesnt work, well.... Wife will be angry and no one needs that!

 

[ianmcd]

Im pretty sure its as simple as connecting the live and earth from the C27 to both BDR91s

BDR91 doesnt have an earth, you might want to use a Neutral, NEVER go with wiring colours on heating sytems

 

[stem]

C27 1&2 go to the BDR91 for heat conections B&C, C27 3&4 to the BDR91 for hot water B&C

With what you propose, you are connecting CH and HW control wires to the same BDR91. For example terminal 3 is a HW control wire and terminal 4 is CH control wire, yet you propose to connect them both to the BDR91 for hot water. The same is true of terminals 1 and 2 if they are actually fitted.

The wires should be moved from the C27 to the BDR's as below:

C27 N & L → Both BDR 91’s N & L (If using 3 core cable isolate/insulate earth wire safely)

C27 ‘1’ → HW BDR 91 ‘C’ (if fitted)

C27 ‘2’ → CH BDR 91 ‘C’ (if fitted - very unlikely)

C27 ‘3’ → HW BDR 91 ‘B’

C27 ‘4’ → CH BDR 91 ‘B’

Link ‘L’ to ‘A’ on HW BDR 91

Link ‘L’ to ‘A’ on CH BDR 91

As you have figured, the old room thermostat can't simply be disconnected as this would leave the heating wiring 'open circuit' and it would not operate, the integrity of the circuit needs to be maintained. As not all thermostats are the same, some working out will be required.

1. Look at the wiring diagram for your make/mode of thermostat that you are removing. If you don't have the instructions for it, a diagram is usually printed inside the lid. This will show which are the two live switching wires, and which is the neutral wire. (If there is a neutral present. Not all thermostats need or have one fitted)

2. Trace the thermostat cable back to its origin.

3. Take take a photo, or make a note of where the live switching wires are connected at their origin.

4. You can now disconnect all of the wires going to the old thermostat and remove the cable and thermostat.

5. Insert a wire link between the terminals where the two live switching wires have just been removed from, so that they are now electrically joined together.

 

[somedudebob]

BDR91 doesnt have an earth, you might want to use a Neutral, NEVER go with wiring colours on heating sytems

Sorry, You are correct. Its even labelled N on both devices

With what you propose, you are connecting CH and HW control wires to the same BDR91. For example terminal 3 is a HW control wire and terminal 4 is CH control wire, yet you propose to connect them both to the BDR91 for hot water. The same is true of terminals 1 and 2 if they are actually fitted.

The wires should be moved from the C27 to the BDR's as below:

C27 N & L → Both BDR 91’s N & L (If using 3 core cable isolate/insulate earth wire safely)

C27 ‘1’ → HW BDR 91 ‘C’ (if fitted)

C27 ‘2’ → CH BDR 91 ‘C’ (if fitted - very unlikely)

C27 ‘3’ → HW BDR 91 ‘B’

C27 ‘4’ → CH BDR 91 ‘B’

Link ‘L’ to ‘A’ on HW BDR 91

Link ‘L’ to ‘A’ on CH BDR 91

As you have figured, the old room thermostat can't simply be disconnected as this would leave the heating wiring 'open circuit' and it would not operate, the integrity of the circuit needs to be maintained. As not all thermostats are the same, some working out will be required.

1. Look at the wiring diagram for your make/mode of thermostat that you are removing. If you don't have the instructions for it, a diagram is usually printed inside the lid. This will show which are the two live switching wires, and which is the neutral wire. (If there is a neutral present. Not all thermostats need or have one fitted)

2. Trace the thermostat cable back to its origin.

3. Take take a photo, or make a note of where the live switching wires are connected at their origin.

4. You can now disconnect all of the wires going to the old thermostat and remove the cable and thermostat.

5. Insert a wire link between the terminals where the two live switching wires have just been removed from, so that they are now electrically joined together.

Yes, Well noticed. 1&3 to one BDR for HW, 2&4 to the other for CH. L to A on both

The Room Stat is a SUNVIC TLM model, and I am assuming is wired to the boiler house (The C27 is on the other side of the house, the boiler on the other side of the wall from the Room Stat) so hopefully shouldnt be too difficult to trace. The Room Stat is also right above the radiator for that room..... Sensible.....

 

[stem]

If it's this model, the live switching wires are connected to terminals 1 and 3. Trace the cable back to its origin; note where the wires that go to 1 and 3 are connected and then disconnect all of the wires in the cable going to the thermostat completely. Finally link the terminals where the wires that went to 1 and 3 have just been removed from.

If your thermostat is different, or you need any help, post back.

As a suggestion you could do the BDR's first & set the TLM thermostat to max to test everything is working OK. Once you know all is well, then you can decommission the TLM.

 

[somedudebob]

Yes. I think that is going to be my way forward, to make sure no mistakes are made along the way. Im going to need to track some cable in the wall as the BDR91s need to be 30CM apart, and need to fit some back boxes to make a nice job of this for mounting them.

Thanks for all the help, at least I know what I need to do with wiring now, just the physical fitting to go. Luckily I have a fair amount of 240v cable lying around.

 

[somedudebob]

So I have finally got round to doing this today and now having finally removed the C27, I only have wires on 3 & 4, Looks like I just connect these to B? But I believe I need a loop from the Second L to A

So that when either heat or HW are called the live joins from L2 to A to B making the circuit?

 

[CBW]

Do you not have a Wireless cylinder thermostat or sensor, or is it acceptable to just use x2 bed 91’s?

 

[somedudebob]

I got s second BDR 91 with the hot water kit. I have the wireless cylinder thermostat fitted, it pairs to the controller. One BDR for CW and one for HW switching

 

[CBW]

I thought it was a CS92, but I’m guessing that if you have a 2nd bdr91, then yes, a link from L to A wil, be required.

 

[somedudebob]

So the CS92, Is the wireless Thermostat, Sends the current temperature of the Stored HW to the Controller, But the controller still needs the BDR91 to switch HW on, when controlling both CH and HW separately (don’t want heating on in summer for hot water etc

 

[CBW]

So as long as it works that way, then each bdr 91 will need L and N, a linked L to A and the signal wires to relevant B’s.

 

[somedudebob]

Managed to get the whole way through successfully to the binding setup. Apparently this system requires you to have a zone valve, which I don’t have (I think its referred to as y plan or gravity fed. So looks like its back to the drawing board