In common with many people, as the weather’s turned colder, I’ve switched on the central heating. My boiler’s not even two years old yet, and is a pretty efficient Vaillant combi model, but like many such systems, it doesn’t have a built in timer. In fact, some combi installations don’t even have a room thermostat, just an on/off switch for the heating.
Some years ago, I replaced the existing thermostat in the hallway with a Drayton DigiStat 3. Even if you’ve never tinkered with a central heating system before, it’s actually a pretty straightforward job, because in many British heating systems, the thermostat on the wall does just one thing – it turns a circuit on and off; that may be a pump that drives water round the central heating system, or it may be the boiler itself, or something a bit fancier, but essentially, the wall thermostat is just a simple switch; you could, if you wanted, replace it with a light switch.
This means that if you want something a bit more sophisticated than a mechanical thermostat, it’s a simple job to replace your existing one. The Digistat 3 that I’m currently using is powered by two batteries, and as well as reacting to the temperature, includes a clock. It can be programmed with different temperatures for different times of the day – morning, daytime, evening and night – and days of the week.
That gives you a lot more control over your heating (and energy use), and combines both the function of a time switch and a thermostat. And it’s possible to add something like this to just about any central heating system because all you have to do is turn on and off a single switch – the boiler doesn’t care why it’s being told to turn the heating on or off, whether it’s time or temperature. The Digistat is just a relay, powered by batteries, and controlled by it’s clock and sensors.
Modern technology
While a programmable 7 day thermostat is perfect for a lot of people, it’s not always ideal for me. For example, sometimes I’ll be working in someone’s office, or spend the day out of the flat. On those days, it’s actually going to be a bit wasteful to have the heating running when I’m not here; it could be turned off, or the temperature turned down a few more degrees, saving more energy.
But, smart though the Digistat 3 may be, it has just four buttons and a small display. Making a change for a single day is a bit fiddly and so, like many people I suspect, I don’t bother. So, whether I’m working at home or not, the heating carries on with the same program.
One solution to that – and perhaps I’ve been talking myself into a new gadget here – is a thermostat that’s remotely controllable via the home network. By providing a web or app interface, it’s suddenly much easier to control than fiddling around with those buttons. It’s even possible to set things up to give me remote control, so I could turn on the heating when I’m just leaving the office, for instance, or stop it coming on if I’m going to be working late.
I’ve been thinking about this because it looks like the faithful old Digistat is on its last legs; last week the relay appeared to be stuck in the ‘off’ position, and this week it died completely for a few hours, prompting me to search for a WiFi thermostat.
WiFi thermostats?
Yes, some of you are probably wondering if the world’s gone mad. But a quick search online revealed that there are several out there, though many are made for the US market, and while they may be available in the UK, or by mail order, that’s not ideal.
One of the main reasons for that is that in the US, systems that incorporate both cooling and heating are much more common; wireless thermostats tend to be a fairly high end product, and so they support all the options. And from a bit of cursory reading, it seems that as a result, the connections to a thermostat in the US tend to be a little more complicated. Of course, you can buy a fancy thermostat that supports aircon as well as heating, and tell it you just have a simple on-off control, but that does seem to be a bit of overkill.
And, you’ll still run into wiring issues; a wifi thermostat isn’t going to run on batteries. The US models that I’ve looked at expect there to be a 24 volt supply available through the thermostat wiring, and that’s not going to be much use to you in the UK. (Though oddly, there are terminals in my boiler that the manual indicates would provide the required power; they’re marked “not to be used in the UK”.)
Wiring up
Fortunately, there are WiFi thermostats available for the UK market too, including several models from Heatmiser, which I’ve been looking at; there’s even an app for remote control. I was sorely tempted by one, with WiFi, 7 day programming and a touch screen. But there’s one sticking point – the need for a 230 volt supply.
To make the Heatmiser WiFi stat work, you’ll need at least three wires, plus earth, coming into the back of your existing thermostat. Then, when it’s connected up, two of those will supply live and neutral to the thermostat itself, and the third will feed back the live supply to the boiler when heating is required.
If you have three core plus earth cable, then you’re all set; you might have to adjust some connections at the boiler end, but at least you won’t have to run a new cable through.
Unfortunately, I don’t. Since my previous thermostats have only ever acted as a dumb switch, the wiring into my thermostat is standard mains cable – two cores, plus earth. I suspect that an awful lot of people are in that position.
It would be possible to replace the wire; it’s not buried behind plasterwork in my flat, but it does run along skirting boards, behind fitted kitchen cupboards, and through the back of a fireplace. Ripping out the existing one could be done, but it’s the sort of DIY that is just a hassle, even if it doesn’t involve the replastering and repainting that many people would find necessary.
Fortunately, it turns out that Heatmiser is working on a new version, which uses WiFi to allow control of the thermosat, but a separate wireless circuit for the actual switching. That means that the bit that actually turns the boiler on and off can be sited right next to it, and the touch screen panel WiFi unit replaces the existing wall thermostat.
Since it’s controlling the switch by wireless, all it needs is power, live and neutral. Which means that the existing two wire connection can be reused to do that, and I won’t have to spend hours trying to coax a new cable out from behind the kitchen cabinets.
They’re going to send me a unit to test, and I’ll write more when I’ve got it.
