Hi all,

My heating install is around 12 years old now, with a piped gas WB 40CDi driving what I have divined to be a pretty vanilla S-plan system, with two separate V4043H valves controlling hot water and heating, a mains-pressure, closed hot water system (i.e. no header tank) with a backup immersion heater and a conventional radiator setup (approx 13 radiators). A single (red) pump is used for moving water around the heating circuit, although there is also a separate bronze pump to feed a DHW circulation loop ensuring that there is always hot water close to the outlets. (I thought this a good idea at the time and my plumber fitted it - 12 years later, I'm still not sure it was a good idea or not!)

I now work from home more often than not and am very aware that during the winter I am heating the whole house when, in fact, I rarely leave my office / kitchen. I thus started to look into various solutions for zone-based control and have settled on Evohome as having the best mix of features and (I hope!) longevity - after all, I'd rather not be replacing this every 3 years when it's suddenly made obsolete!

My current plan is to purchase and install the following, which I think will suit my requirements:
1 x Evohome wifi connected controller
1 x BDR91 (heating control relay)
13 x HR91 / HR92 TRVs
1 x 10 way junction box
1 x Hot water system (BDR91 + wireless temperature sensor)

In the boiler room, I will replace the existing Honeywell 7-day clock and Honeywell "wiring centre" with a conventional 10-way junction box and pair of BDR91s. The new temperature sensor will be fitted to the tank, although this is actually only about 2ft from the boiler. Due to space, the two BDR91s were planned to sit next to each other, but I could probably separate them by 18 inches or so by putting one where the existing timer is, and the other below the immersion timer switch near the red pump (see photos). This will follow the "standard" S-plan wiring, with the BDR91s controlling the valves, and the valves controlling the boiler itself, more or less mimicing the existing wiring.

Around the house, all radiators will get new TRVs (HR91 or HR92?) including the radiator in the hallway which currently has no TRV due to its proximity to the existing room thermostat. To ensure that a pumped water bypass path is still in place, the downstairs cloakroom radiator will have no TRV fitted and will be heated with latent heat from the demand created from the rest of the system. Should this prove problematic (i.e. turns the cloakroom into a sauna!), I will get a plumber to install a proper ABV loop instead and this room will get a manual TRV.

This lot will be configured into 11 zones with only the kitchen containing multiple (3) radiators and the downstairs cloakroom having no smart TRV.

If it's not already obvious, I'm not a plumber, but am reasonably confident that I can do the electrical side without a problem. (Put it this way, the existing wiring isn't exactly neat and I'm pretty sure I can do better than that!) Probably my biggest concern here is comms stability as my house consists mostly of brick internal walls and it'll be a reasonably distance from the kitchen (where I assume we'll keep the controller) to the loft room (the most distant radiator). I've also not decided yet whether to get HR91 or HR92 TRVs.

I'm very interested to hear any feedback or suggestions of things I may have missed, or am doing completely wrong, ideally before I go ahead and spend lots of money!

Some pics:

Boiler and expansion vessels (shoes are sat on top of the hot water tank):
20190902_155352.jpg

Timer + valves (tank is to the left):
20190902_155403.jpg

Existing timer wiring:
20190829_164742.jpg

Proposed S-plan wiring:
nReqvWH.jpg