Honeywell Evohome - Multi-Room Zones

When we installed the Honeywell Evohome central heating control system we fitted four radiators with HR92 temperature regulating valves (TRV). In the other rooms we left the manual TRVs fitted, and lived with the fact that whenever the Evohome system decided that any of the controlled rooms were getting a bit too cold, then the manual TRV rooms would be getting some heating. So recently we ordered another pack of four HR92s from JTM Plumbing, and have fitted them to the remaining radiators. We didn't do this originally purely because of cost, as the HR92s are not cheap, but the ability to add new HR92s to the system means you can fit out the whole house as and when we can afford it.

As our radiators already have the M30x1.5 valves, installation of the HR92s was as easy as before. Binding them to the Controller was also really straight forward. A long press on the Settings icon is required to get into the system settings menu. Then simply add a zone and give it a name, at which point the Controller will sit and wait for the HR92 to start the binding process. (The only thing to remember is to tell the Controller not to use the temperature sensor in the Controller itself for this new zone.) On the HR92 a couple of presses of the button are required to get it into binding mode, and within seconds the Controller was reporting that the two were bound.

We have an open plan L-shaped lounge and dining room, with a radiator in each 'room'. Previously only the lounge radiator had a HR92, but now both of them have HR92s fitted. We started by copying the temperature schedule from the lounge to the dining room, so that both radiators would be trying to keep this space at the same temperature. This is easily accomplished, by going into the schedule for the lounge zone, and using the icon in the bottom right of the Controller display to copy the entire week schedule to the dining room zone.

However this does mean that if we change a schedule or manually change the temperature setpoint in one of the zones, the other zone is unaffected and the two radiators will be trying to keep the one space at two different temperatures. So we set up a multi-room zone, using both the lounge and dining room radiators. The Controller now allows only one temperature setpoint and schedule for the space as a whole, but the two radiators work independently to achieve the desired temperature. This works really well at dealing with the different thermal characteristics of the space. Our lounge is on the south side of the house with big windows and a wood burning stove in it, while the dining room is on the north side of the house with very little natural warming getting in. Certainly when we fire up the stove, the lounge radiator pretty much shuts down as the stove warms up the lounge. We'll have to wait and see how the system deals with sunny days (I hope!).

Honeywell Evohome - Installation

We've started installing a Honeywell Evohome system in the house for our central heating and hot water. So far so good, although with some stumbling points along the way.

When we bought the house we inherited a gas-fired Potterton Suprima boiler hooked up to a Sundial Y-Plan system with a mid-position valve to heat up a storage tank for hot water, and water radiators in each room. There was a truly ancient 24-hour programmable timer, and the thermostat for the entire house was located behind a door in the entrance hallway. Consequently the house was simultaneously too hot and too cold, cost an arm and a leg to run, and within a month of moving in the whole system died just as the winter snow started falling.

The Evohome system comes in functionality packs, so we needed the Base Pack (a Controller and one BDR91 Wireless Relay), a Hot Water Pack (a CS92 temperature sensor and another BDR91 Wireless Relay), and a Radiator Multi Zone pack (four HR92 temperature regulating valves). We bought these in from JTM Plumbing, who provided an exceptionally quick delivery service and very keen pricing.

In the airing cupboard we removed the wired thermostat from the hot water cylinder, the 24-hour programmable timer from the wall, and unwired the mid-position valve and Grundfos Alpha2 water pump. To the hot water tank we fitted the CS92 temperature sensor, and ran the cable to the CS92 transceiver which was screwed to the wall. We then fitted the two BDR91 wireless relays to the wall, and proceeded to rewire the various components up according to the Y-Plan wiring diagram on page 47 of the Evohome installation manual (doc ref 50040745-201 A).

There were two issues with the wiring that we needed to resolve. The first was that the Honeywell wiring diagram has an error. The BDR91 for the hot water shows an unlabelled connection, which is actually to the C contact. The Evotouch was the Honeywell product that the Evohome Controller evolved from, and the manual for the Evotouch shows the same Y-Plan wiring diagram, with the connection to the C contact labelled correctly. I can only assume the cut-and-paste between manuals introduced the error.

The second issue was that the wiring for the Suprima boiler requires an always-on power supply, and then a switched live connection to get it to fire up. The boiler can also provide power to the Grundfos pump, presumably to ensure that water is circulating when the boiler is heating water. So we tapped into the power from contact 1 in the junction box, and used contact 8 for the switched live supply to the boiler. We also chose to disconnect the Grundfos pump from the boiler, and connect it to contact 8, as per the Y-Plan wiring diagram.

In terms of wiring, that's the extent of the work. Apart from a small bit of redecorating where we removed the old thermostat from the wall in the hallway, all of the work was in the airing cupboard and out of sight. The only other installation required was to fit the HR92 TRVs, which for us just required screwing them onto the M30x1.5 valves on each radiator. The HR92s separate into two parts, one of which is threaded for installing on the valves, and then the main body then just slides into place on top, with a sliding lock to keep them in place.

Now we just need to configure the system!