In summer you can turn your central heating off without a second thought, and nearly everyone should, because there is no sense in warming a house that is already warm. The question people really mean, though, is whether to switch the whole boiler off at the unit, and the plain answer is that it saves almost nothing and can cause more bother than it is worth. A modern boiler sitting idle in warm weather costs pennies. What matters far more is making sure it is set to heat water only, rather than quietly standing ready to fire for heating that nobody needs.
The short answer. Turn the central heating off over summer, yes. But switching the whole boiler off at the unit saves only a few pounds a year at most, because a modern boiler uses next to nothing when it is not firing. On a combi, use the summer or hot water only setting so it still heats water on demand but never fires for heating. On a system or regular boiler, keep hot water on a short timer. Leaving the boiler on standby also keeps the pump and diverter valve from seizing over the quiet months, which is the real reason not to kill it at the switch.
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Heating off, yes. Boiler off, probably not
These are two different actions and it is worth separating them. Turning the heating off means telling the boiler not to warm your radiators, either by dropping the room thermostat well below room temperature or by switching the heating side off at the programmer. That is the sensible summer move, and it costs you nothing in comfort because the house does not need heating anyway. Turning the boiler off means cutting power to the whole appliance at its own switch or the fused spur, so it does nothing at all, not even keep its pump turning over.
The first is obviously worth doing. The second is the one people agonise over, usually in the belief it is quietly costing them money just by being plugged in. For a modern condensing boiler that belief is mostly wrong, and acting on it can leave you with a seized pump come October. So the useful question is not whether to turn the heating off, which you should, but whether killing the whole unit earns its keep.
What a boiler actually uses when it is idle
Old boilers had a permanent pilot light, a small gas flame that burned around the clock and did cost a noticeable amount over a summer. Those have all but gone. A modern condensing boiler lights electronically only when it needs to fire, so when it is sitting idle in July it burns no gas at all. What it does use is a trickle of electricity to keep its controls awake, ready to respond when you run a hot tap.
Put a number on it. Say the electronics draw about 3 watts while idle. Over a year that is 3 × 24 × 365, which comes to roughly 26 kWh, and at an example electricity rate of 26p per kWh under the current Ofgem price cap for October to December 2026, that is about £6.80 a year. In summer specifically you are talking a couple of pounds. The gas side contributes essentially nothing when the boiler is not firing. So the entire prize for switching the boiler off at the wall for the summer is somewhere around a pound or two, and only if you also give up instant hot water.
| State | Gas used | Electricity | Rough summer cost |
|---|---|---|---|
| Heating off, boiler on standby for hot water | Only when a tap runs | ~3 W idle | A pound or two in standby |
| Boiler fully off at the switch | None | None | Saves that pound or two, loses instant hot water |
Illustrative figures at an example rate of 26p per kWh. Your boiler's standby draw varies by model; a plug-in monitor cannot read a hard-wired boiler, so these are typical estimates rather than your exact numbers.
Combi boilers: use the summer setting
If you have a combi, which heats hot water on demand with no tank, you almost never want to switch it off at the unit. Instead use its summer setting. Most combis have two dials or two symbols on the display, one for central heating and one for hot water, often a radiator icon and a tap icon. Turn the heating one right down or off, and leave the hot water one on. The boiler then ignores any call for heating but still fires the moment you turn on a hot tap or shower.
This gives you everything you want. No radiators coming on during a warm spell, instant hot water whenever you need it, and the pump still turns over when the boiler fires for a shower, so nothing sits stagnant for three months. It is the setting the boiler was designed to use in summer, and it is why reaching for the main off switch is almost always the wrong move on a combi. For how the heating side should be programmed the rest of the year, the central heating timer settings guide covers it.
System and regular boilers: the hot water question
If you have a system or regular boiler feeding a hot water cylinder, the summer setup is slightly different because your hot water is stored, not made on demand. Turn the heating off at the programmer, then set the hot water to come on for a short window once a day, enough to reheat the tank for showers and washing up. You do not need it on all day; a well lagged cylinder holds its heat for hours, which is the whole point of the timer versus constant debate, and the timer wins comfortably in summer.
You could instead heat the water with the immersion heater and leave the boiler alone entirely, but that is usually the dearer route, because immersion heating runs on electricity at around 26p a unit against gas at roughly 7p. Unless you have cheap off-peak electricity or solar diverting to the tank, gas heated water from the boiler on a short timer is normally the cheaper summer option. Either way, keep the cylinder at a safe temperature; the cylinder temperature guide explains why 60 degrees matters for the tank even in summer.
The real reason not to switch it off at the unit
The strongest argument against killing the boiler for the summer is not the pennies, it is mechanical. A central heating pump and the diverter valve inside the boiler can stiffen or seize if they sit completely still for months, especially in an older or hard water system where a little scale and sludge is present. Plenty of people discover this in autumn, when the heating is switched back on for the first cold night and the pump refuses to turn or the valve sticks halfway, and what should have been a free restart turns into a call-out.
Leaving the boiler on standby through summer sidesteps this neatly, because it still fires for hot water now and then and the pump turns with it. Many boilers also have a built in seize protection feature that runs the pump briefly every so often, but only if the unit has power. Switch it off at the wall and that protection stops too. So the small standby cost is really buying you insurance against a stuck pump, which is a trade almost always worth making.
What turning it off actually saves
Pull it together and the honest figure is deflating for anyone hoping for a big summer win. Switching the whole boiler off might save you a pound or two of standby electricity over the season. Against that you lose instant hot water, you give up the pump's gentle exercise, and you take on the small but real risk of a seized pump or valve when you fire it up again. There is no meaningful gas saving to be had, because a boiler that is not firing is not burning gas in the first place. The money in summer energy is not in the boiler's standby draw; it is in the hot water itself, in how long and how hot you run the shower, which is where the biggest gas users really sit.
Better things to do with your boiler in summer
If you want summer to actually trim next winter's bills, there are better jobs than flicking the off switch. Book the annual service in the quiet months when engineers have more slack and sometimes better prices. Turn the hot water flow temperature down a little if your household can live with it. And when the heating does go back on, take ten minutes to lower the central heating flow temperature on a combi, which is one of the cheapest ways to cut gas use with no loss of comfort, as the flow temperature guide explains. If you want the full seasonal run through, the summer energy checklist covers the lot.
What I would actually do
On a combi, I would leave the boiler on and move it to its summer setting: heating off, hot water on. On a system boiler, I would turn the heating off at the programmer and put the hot water on a short daily timer. I would not switch the whole boiler off at the wall, because the saving is a pound or two and the downside is a pump that might not wake up in October. The genuine summer savings come from the hot water, from a service booked cheaply, and from a lower flow temperature when the heating returns, not from chasing a few watts of standby. For what your boiler costs to run the rest of the year, the gas boiler running cost guide has the numbers.
Common questions
Should I turn my boiler off completely in summer?
There is little point. A modern boiler burns no gas when it is not firing and uses only a few watts of electricity on standby, so switching it off saves maybe a pound or two over summer. You also lose instant hot water and risk the pump seizing. Turn the heating off, but leave the boiler on standby.
Does leaving a boiler on standby cost much in summer?
No. With no pilot light on modern boilers, an idle boiler uses only its control electronics, roughly 3 watts, which is around a pound or two of electricity across the summer at an example rate of 26p per kWh. The gas side costs nothing when it is not firing.
What is the summer setting on a combi boiler?
It means turning the central heating down or off while leaving the hot water on. Most combis have separate controls for heating and hot water, often a radiator symbol and a tap symbol. Set it this way and the boiler never fires for heating but still gives instant hot water.
Why can turning the boiler off cause problems?
If the pump and diverter valve sit completely still for months they can seize, especially in older or hard water systems. Leaving the boiler on standby keeps the pump turning over when it fires for hot water, and keeps any built in seize protection working, which needs the unit to have power.