Horstmann - CentaurPlus C27 - Series 2 - Two Channel 7 Day Programmer

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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

Horstmann CentaurPlus C27 Central Heating Programmer Horstmann CentaurPlus C27 Central Heating Programmer

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 AThe Boiler is a Grant Vortex Pro External Combi21e, as the name suggests the boiler is outside in a casing so it's a bit more difficult to trace the wiring. We have bought a new Nest Thermostat to replace our current Horstmann C27 which runs our Central heating and Hot Water on a timed system, we have a Netaheat Profile 303 Boiler. The Nest Heatlink will need the usual Live and Neutral, from the same supply as the programmer etc, for it's power. note it says Centaur Plus is volt free, so it seems the centaur plus is same as Hive single channel and standard one is same as Hive duel channel, so I would be hunting on the actual device to see if there is a diagram. Your picture clearly shows a brown sleeve on the blue wire going to 3 so clearly a line not neutral.

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With most leccy flow through boiler systems Rob; the HW is just heated by the immersion heaters, to confirm this do you have two immersion heaters? 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)This seems to be the other end where the programmer is (the white cable with the blue wire with yellow tape around it) 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. If that's all correct then what do I need to connect the hot water and central heating commons on the nest heat link. I'm reading about jumpers from the live? 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? Override: 1 hour boost (Hot Water only), 1 hour extension to On period (Hot Water only), instant advance (Central Heating only)