by ericmark »
Fri Feb 21, 2020 3:10 pm
For most programmable thermostat you will only need the red and yellow wires, as you say battery powered so does not need neutral. But with any wireless thermostat (Except Nest e) you will need the neutral, so need to put unused wires safe so in the future you can use them.
I fitted the Flomasta 22199SX Wired Digital Programmable Thermostat (Screwfix number 6259G) which has worked well in last home, with a wired thermostat no need for expensive types, but with wireless the cheaper ones don't fail safe, i.e. if battery goes flat central heating defaults off.
You can split thermostats into groups.
1) Simple on/off, mechanical still very good for when using TRV heads to control, as the large difference between on and off means can be set so it just stops cycling in summer.
1A) As above but electronic so difference on/off drops from around 1.5°C to 0.5°C.
2) Programmable hard wired on/off, means no need for frost stat, and you can keep a back ground heat so does not take too long to reheat, some have more slots than others.
3) Anti hysteresis on/off thermostats, these start switching off/on before the target temperature so it does not over shoot, Honeywell Y6630D is a good example seems over priced at first glance, but has both anti hysteresis and fail safe software, but not programmable.
4) Wireless as with Y6630D with some models you can use free standing I got the Horstmann which spec seemed great, but found it would loose RF link and room sitting at 30°C.
5) Connects to the thermostatic radiator valve, Hive, Energenie, Evohome, Wiser, etc.
6) Connects to boiler using the ebus Nest, Wiser etc.
7) Uses geofencing and occupancy detection Nest etc.
Once you hit the £100 mark then the whole idea moves to connecting to phone, however in the main we want to save energy by not using heating while not using the area, and also not over heating the room.
This can be a lot cheaper than you think, the Eqiva eQ-3 TRV head starts at around £10, I have the bluetooth version cost me £15 each, so I can set the maximum temperature of each room independently and really easy to fit, OK it will not turn the boiler on or off, but the modern modulating gas boiler will auto turn down as the return water heats up, so often not required to turn boiler on/off, a very simple wall thermostat like you already have will do that.
With systems like EvoHome the TRV talks to the wall control which in turn talks to boiler, really cleaver, but not convinced we need that much control?
So my house the programmable TRV in the hall has the same schedule as the programmable wall thermostat so switch the boiler on/off at regular intervals when heating is wanted, and the programmable TRV heads control each room.
I know it is not what you asked, but they go together, I walk into bedroom straight to the radiator and press the eco/comfort button if not at the scheduled time, yes I have Nest, but it is not Nest that ensures each room at set temperature it is the TRV heads. I have 9 programmable heads which control all the main rooms, so for example the dinning room is only set to switch up temperature at 4 pm.
When I open kitchen door to unload car, the cold draft hits the TRV head and it auto turns off for 20 minutes as I unload car then back on again to reheat kitchen. Cost £15 and just unscrew old and screw on new. No wires. Just fit batteries and set the schedule.
