Gradual conversion

[Azalea]

Hi

I'm looking to convert our house to wireless and evohome heating control but had a few questions before I made my investment.

I have tried looking through the forum and answered some questions, but others I couldn't work out. Apologies if these have been asked before.

At the moment I have a heating system that seems a bit more complicated than most - I have a 7 day programmer controlling a system boiler for hot water, 2 central heating zones and an underfloor heating zone. I guess this is an s plan plus? Each heating zone has its own dt90 thermostat. The central heating zones replaced an ordinary thermostat so I'm not sure which wires they left behind, but the underfloor heating thermostat was newly wired when the pipes were laid.

I don't think I can afford to convert the house completely in one go so wanted to do it in stages.

Initially I'd like to buy the hr92 trvs and control them using the evohome controller. Would the evohome controller work if there is no bdr91 (ie just used to set the trvs)?

I understand that the two central heating zones would become redundant. Initially I thought we could replace one of the existing dt90 thermostats with a bdr91 and get someone to link or bypass the zone valves, but am I correct in thinking this won't be possible since I'm not sure that the thermostats have a mains live wire behind them? In which case the easiest location seems to be next to the 7 day controller or next to the boiler itself. What is the maximum wireless range?

The hot water and underfloor heating work just fine as it is, so eventually I see the existing 7 day programmer controlling just the hot water and underfloor heating, with evohome controlling the rest. Does this seem reasonable?

Thanks in advance,


A.

[Richard]

Hi Azalea,

Welcome to the forum.

We have a written overview of the evohome system here - https://theevohomeshop.co.uk/content/8- ... -do-i-need

As for your system, yes you have an S Plan Plus. The downside of having an S Plan Plus, is that you have to think about the system a little more and how evohome will operate in it. evohome likes to be in charge of everything, so if you do attach it to an S Plan Plus system without it controlling the entire system, there are zone demands outside of the evohome system that evohome will not know about. These demands outside of evohome's control will mean evohome won't work as well as if it was controlling each zone.

The HR91 and HR92 Radiator Controllers are in control of zone demands, and the way the system deals with this is by a BDR91 (Boiler Demand Relay) telling the boiler it needs to come on at this point. The diagrams in the evohome Installation Guide (you can download from this page - https://theevohomeshop.co.uk/content/11-evo-help) page 44 show you how this is done (but varies boiler to boiler).

If you are unsure, contact a connected specialist to help you install the system - https://heatingcontrols.honeywellhome.c ... installer/

I hope that helps.

[Azalea]

Thanks for taking the time to answer and pointing out those references, which I had previously had a look at.

I don't think I've been clear. Initially I just wanted some connected TRVs linked to in room thermostats not linked to the boiler. Ie use the evohome controller without the boiler relay, but just to set up the room zones. Does it let you do this?

You have mentioned that the evohome not knowing about other zone demands makes it run less efficiently, but I really don't understand why this should be? Why does it make a difference to our central heating whether the hot water/underfloor is running if the central heating is being controlled by a zone valve?

A.