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!
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