Smart heating

We explain what to happens to smart thermostat systems and zoned smart-heating when there is a power cut or the Wi-Fi breaks. Includes Nest, Hive, Tado, Netatmo, Honeywell, HeatMiser and Heat Genius.

Smart heating is great, and coming soon to a house near you. The ability to control the temperature of your home from laptop, smartphone or tablet is both a cool function, and a great money-saving device. Heating only where you need, when you need it is going to become a big deal in the next few years. Not least because it suits the utilities to conserve fuel. Expect your provider to start promoting smart heating, even if it isn't yet doing so.

This is all great when it works. But just as you can't tune a digital TV is the signal is slightly out, smart home functionality is an all-or-nothing proposition. Recently the broadband stopped working in my home and, as well as the usual panic over lack of communications and entertainment, it meant that the heating stopped working.

Actually, it very quickly became apparent that lack of Wi-Fi didn't mean a lack of heat, but it pays to know what will happen in the eventuality of a power cut, the internet going down or the batteries runing out. Heating after all isn't an optional extra to be casually discarded when the power goes out. So here is what we learnt about what happens to smart heating when the lights go out.

For more on which smart-heating system is best for your home, see: 7 best smart heating systems of 2014.

What happens to smart heating when there's a power cut?

You lose the smartness, but the dumb heating keeps working. Or at least, the heating works as it has always worked after a powercut. This means that in most cases you will not be able to use the heating after a powercut. Only very old heating systems can operate without power.

This is a shame, because in almost all cases the smart controller has to have a battery backup so that the smart element of your heating should continue to work just fine. You won't be able to control the heating remotely, or set a new heat regime, but if by some miracle your central heating doesn't require current to operate, you will be able to flick the heat on or off. Like you used to have to.

But in all probability you are going to be cold. I'm indebted to reader Chris Riley for pointing this out.

What happens to smart heating when the batteries run out?

Again, in almost all cases smart heating doesn't rely on batteries. The batteries in smart thermostats such as those of Nest and Hive exist only as backups and should never be required unless the power goes out. As a consequence they should never need to be replaced. But if they do, the thermostat will tell you in good time. The exception to this is HeatMiser Neo and Heat Genius, both of which are zoned smart-heating tools that use smart TRVs to operate each radiator separately.

In those cases you will need to replace the batteries in the TRVs from time to time. Again the systems will let you know in good time that you need to install new batteries. And if the batteries aren't replaced the TRVs will be left in the 'on' position, so that you will have a surfeit of heat rather than not being able to operate the heating.

What happens to smart heating when the Wi-Fi is down?

We'll get into specifics in a minute, but in general a lack of Wi-Fi affects only the way that you can communicate with the heating and not the heating's ability to operate. In the cases of the smart thermostats it generally follows that the heating will continue to act as it did before, and your problem will be with your ability to change the schedule. With the more sophisticated zoned heating systems you will generally find that you have to disable the central hub and use manual controls.

What happens to Nest Learning Thermostat, Hive Active Heating, Tado, or the Honeywell Lyric thermostat when the power is off or the Wi-Fi is down?

As mentioned above, if the power goes down the smart thermostats have batteries as a backup power source that kick in and keep things working (although your heating is probably not going to work). If your backup batteries do get low, you'll get a notification on the thermostat itself and via any app you use to control it.

In each case your heating will continue to work if your broadband goes down. Taking Hive as an example, if your system is in Auto mode it will continue to run to the heating schedule that you have set. In all cases you can control your heating settings manually from your thermostat until your broadband connection is restored.

What happens to Heat Genius and HeatMiser Neo smart heating when the power or the internet is down?

As before lack of internet means only that you lose control. You can't then use the mobile app to control things. But neither Heat Genius or HeatMiser Neo uses your Wi-Fi to operate, instead building their own networks. So in the case of Heat Genius the Genius Hub will keep trying to communicate with the boiler which prevents manual operation, but unplug the Hub and you can use the manual controls. Once the broadband is back, plug in the Hub and it will work as before.

As mentioned the smart TRVs are powered by battery so they will continue to work fine in a network outage. And if the power goes down you should find that the manual controller on the boiler has a backup battery that kicks straight in. (See also: Hive or Nest: which is the best smart thermostat?)