Should you turn your boiler off at night?

Turning your boiler off at night might seem like common sense to save some money. With decent insulation and all your double-glazed windows closed, the home will probably stay warm enough for a few hours after bedtime. Since you won’t be using any hot water as you sleep, either, you may as well switch off your boiler. 

Right?

The truth about whether you should turn your boiler off at night isn’t as simple as that. And if you’re switching it off for economic reasons, we hate to be the bearer of bad news, but you might not be saving much money at all.  So here’s what you need to know about the impact of turning your boiler off overnight.

Is it OK to turn your boiler off overnight?

Boilers do turn on from time to time during the night, so turning it off stops it running as you’re sound asleep. 

Combi boilers work best when the heat exchanger inside is kept warm. So, it will need “topping up” a few times overnight to make sure you have instant hot water when you need it. 

With a system or heat only boiler, it’s the cylinder that gets heated up when its temperature drops and the thermostat tells the boiler to fire up (assuming it’s not on a timer).

Many people don’t use much hot water from the tap, either. Your dishwasher, washing machine, and shower heat water on demand, and your kettle and coffee machine make your morning drink from cold tap water, too. So, apart from half an hour waiting for the radiators to warm up, is there any need to leave the boiler on overnight?

The downsides of turning it off

If you’re not heating water, you’re not burning gas, and if you’re not burning gas, you’re not spending money. But before you go full steam ahead and turn it off, there are a couple of key considerations:

1. How well insulated is your home? 

If you have loft insulation, cavity wall insulation, double- or triple-glazed windows and good sealing around your doors and windows, your home should retain a good proportion of its heat, at least for a few hours.

But if any of these are lacking, your home could drop in temperature quite quickly with no new heat being generated. As water condenses on your walls, that could mean damp issues. Not only does this increase heat loss, but it could also cause structural or cosmetic damage. And that comes at a price. In more extreme circumstances, you could get frozen pipes, which could be much more of a headache, and a more expensive one at that. 

2. The cost of bringing temperature back up

Second, there’s the cost of bringing your temperature back up to a comfortable 18–20 °C in the morning. If your home’s temperature has sunk to below 10 °C overnight, your boiler is going to have to work extra hard to warm up in the morning. But if the boiler was ticking over with the thermostat on, say, 15 °C, it wouldn’t have as much work to do in the morning.

That’s not to say that it would be cheaper to leave the boiler on, or that you’d use less gas. Neither claim would be true. But you might not be saving quite as much as you think you are, because of the extra energy required the following day. So, whether turning your boiler off saves money depends on factors that are out of your control, such as the weather and temperature.

Use our blog to learn more about establishing the ideal room temperature.

Using controls to turn your boiler off overnight

It is entirely possible to have your boiler effectively switched off overnight without physically isolating the power. This can be done in two ways using your controls:

Thermostat

You can set your thermostat to its minimum temperature before you go to bed in the evening. If you want to be sure the heating doesn’t come on, set the temperature as low as it will go. It’s unlikely the heating will come on unless the temperature in your house falls dramatically.

Alternatively, you can set the thermostat in its mid-range - for example, 12–14 °C. Most nights, it probably won’t switch the heating on, but there will be a safeguard for extremely cold nights. That way, you can help protect your home from the risks mentioned above, and on average, you’ll save money.

Understand how to get the most from your thermostat - Boiler thermostats: A complete guide.

Timer

All modern boilers come with a timer on them, usually on a separate panel that’s wired up to the boiler itself. You can set the on and off times for every day of the week. For instance, to turn off at 11pm every night and come on at 7am every weekday (8am on the weekends). The timer will override the thermostat, so even if the temperature drops below the setting you have it on, the heating will not switch on.

Effect on pre-heating water

The timer and the thermostat should not affect the preheating process or a combi boiler. You might hear your boiler fire up from time to time, even when the heating is off and you’re not drawing any hot water. This is completely normal, and is there to ensure you have hot water when you turn it on. If there’s no pre-heat, you might find you have to run the hot tap for 40–60 seconds before any hot water comes out. If you’re trying to save water, that’s not a good thing.

Have you got an immersion heater?

One final thing to consider is the presence of an immersion heater in your system or heat-only cylinder. Your boiler heats up water and circulates it around your cylinder to warm the water inside. But you can also get immersion heaters, which are essentially kettle elements sticking into the cylinder (it’s a bit more complex than that, but not much). That means you’re using electricity, not gas, to warm up the water. 

Why would you do that? Well, if you have an electricity tariff that gives you cheap overnight electricity, you can wake up to a full tank of water without using a single cubic inch of gas, and this might work out cheaper given the tariff. Just make sure your cylinder is well insulated, as a poorly insulated cylinder will leak heat and the immersion heaters will come on more often. 

Also remember, this has nothing to do with your central heating. So if you want hot radiators in the morning, you’ll need to leave your boiler on – just use a timer to wake it up before your alarm clock wakes you up.

So, should you switch it off?

All that’s left to do is decide whether turning your boiler off or keeping it on overnight is right for you. Whatever you choose, we hope you sleep soundly and wake to a warm house this winter. For more ways to keep your boiler working effectively, head to our tips and advice page. And for further support, please get in touch with our team.