Honeywell BDR91 to Honeywell 42005748 Sundial Wiring Centre (S Plan)

[Svenedin]

Hello,

This is my first post on the forum. I do quite a lot of DIY and I am planning to install an Evohome system.

My current set up is a Glo-Worm Flexicom 35 Hx heat only condensing boiler on S-plan (1x motorised valve for HW, 1x motorised valve for CH), 1x wired room thermostat, 1x wired Cylinder stat (vented indirect cylinder) and a 2 channel programmer. Everything is wired together via a Honeywell Sundial Wiring Centre (the type with labelled connecting blocks and links that can be cut). The wiring is exactly as would be expected according to the wiring centre instructions except that the pump is run directly from the boiler itself (it requires overrun and has an automatic bypass). Links 1, 2, 3 and 4 are cut.

Everything works exactly as it should at the moment and is a tidy installation. I am aiming to connect 2x BDR91's for CH and HW and a number of HR92 radiator valves as well as the wireless cylinder stat unit and the Evohome display/control unit. I cannot fit HR92's to all of my radiators as a few are very elderly and on microbore and do not have TRV's (these I intend to replace on 15mm with TRV's at a later date).

My question relates to how to wire the CH and HW BDR91's into the Sundial wiring centre. I would be removing the old programmer and both cylinder stat and room stats. The only diagram I can find relates to the Honeywell 10 way junction box. I could rewire everything using one of those and I am capable of doing that but since everything is neat and tidy as it is it would make more sense (to me at least) to use the existing wiring centre. The trouble is I am not sure how to do it!

It seems to me that I need to take permanent Live and Neutral feeds to the BDR91's and these could come from suitable terminals in the wiring centre (such as the programmer block). Also connect L to A within BDR91. Then I could connect output "B" (switched live) to "HW ON" and "CH ON" in the programmer block of the wiring centre. The BDR91's would effectively be acting as the programmer. I would need to connect 1 and 3 in the room stat block in the wiring centre as there would be nothing attached there.

I would be grateful for some guidance. I have found some old posts with a similar question but it was not the same set up as mine.

 

[stem]

The wiring that currently goes to the existing room thermostat is relocated to the BDR91 relay box as below. [The terminal numbers I have shown on the 'existing stat' diagram assume that it is a standard Honeywell thermostat using 1=Live, 2=Neutral, and 3= Switched live. Other manufacturers may use different identifiers]

As during your modifications the old programmer that presently provides the 'live' to the thermostat is removed, then the live wire (from wiring centre room stat 1) will cease to be live, so the live wire to the BDR91 should be moved to a permanent live in the wiring centre as you have figured. [The L terminal of the removed programmer could be utilised for this.]

Edit
The BDR91 replacing the cylinder thermostat, is similar but you will probably need to add a new neutral for the BDR91 as basic cylinder thermostats don't require one. [The N terminal of the removed programmer could be utilised for this.]

 

[Svenedin]

Thank you very much for taking the time for such a brilliant reply and the diagrams!

In the present set up the heating and hot water will only fire the boiler if both the programmer timer is in an ON period (timer) and the respective thermostat is closed.

If wiring the BDR91’s to the room stat/cylinder stat block you mention providing a permanent live because this will not be coming from the programmer. Would a solution be to wire a permanent live to the programmer CH ON and HW ON terminals? This would have an effect as if there was a programmer attached but permanently in an ON period (but boiler will only fire when thermostat closes). Then the live could come from room stat/cyl stat via wiring centre block.

Stephen

 

[stem]

The BDR91's need a permanent supply. Provided that it comes via the same 3A fused connection unit as the rest of the heating system you connect it at any convenient point. A permanent live to the programmer terminals 'CH ON' and 'HW ON' would do this by supplying a permanent live to the two sets of thermostat terminals meaning that the 'live' wires in room stat '1' and cyl stat 'C' could be left as they are.

 

[Svenedin]

All is up and running as intended! Finally I have the control over the heating and hot water that I have always wanted. Let's hope this leads to lower bills.

 

[stem]

Well done! glad to hear it's all sorted. It's nice to have a thread from someone who understands what they are doing, and thanks for the feedback too, it helps others that may come across this thread when searching for help with their projects.