Is it cheaper to leave a heat pump running? Short answer: usually, yes. Unlike a gas boiler, an air source heat pump is generally cheapest when it runs steadily at a low temperature rather than being switched on and off twice a day. The Energy Saving Trust advises heat pump owners to keep the pump on for extended periods and use a “set-back”, which means turning the room temperature down by a few degrees overnight or when you are out, instead of switching the heating off. The Trust says leaving the pump on for longer does not raise your overall running costs, because the heat pump runs more efficiently and that offsets the longer running period.

That advice surprises a lot of people, because it is the exact opposite of what you were told about a gas boiler. This article explains why the answer flips between the two systems, how to set up a set-back properly, and the handful of situations where leaving a heat pump running all day is not the cheapest option after all.

Why the answer flips between boilers and heat pumps

Start with the boiler, because the confusion begins there. The Energy Saving Trust is blunt: “If you have a boiler, then no. Keeping your heating on all the time will use more energy and cost you more money. It’s more energy efficient, and better for your bills, to have your boiler come on when you need it.” A boiler makes heat by burning fuel at a fixed, high temperature, so the cheapest way to run one is to heat the house only when you need it and let it cool down the rest of the time.

For a heat pump, the very next sentence on the same Energy Saving Trust page reads: “But if you have a heat pump, then you can save money by leaving the heating on all day.” The Trust even lists “heat pumps work best when left running all day” as one of the key things to know about heating. The reason is that a heat pump does not make heat the way a boiler does; it moves heat from the outside air into your home, and it does that most efficiently when it runs gently, steadily and for longer periods at lower flow temperatures. The Trust’s at-a-glance summary puts it plainly: “Keeping a steady temperature, running your heat pump for longer periods and lowering flow temperatures can improve efficiency and reduce costs.”

So the folk wisdom about heating, which was written for boilers, does not transfer. Treating a heat pump like a gas boiler is one of the classic UK installation and usage failings the Trust warns about, and it is a recurring reason bills come in higher than expected. Our guide to the most economical way to run an air source heat pump walks through the full set of settings.

What a set-back is, and how to set one up

A set-back is the compromise between leaving the heating on full all day and switching it off completely. Instead of turning the pump off overnight or when you go to work, you lower the room temperature by a few degrees and let the pump tick over. In the UK, the Energy Saving Trust notes, we are used to turning heating on in the morning, off when we go to work and back on again in the evening. In Europe, people are more likely to keep their heating on for longer and simply lower the temperature by a few degrees overnight or when out. “This is a good strategy for controlling heat pumps, which is known as a ‘set-back’.”

Setting one up is straightforward. Keep your normal comfort temperature where you like it; the Energy Saving Trust suggests setting the room thermostat between 18 and 21 degrees to balance comfort and savings. Then programme a set-back of a few degrees for the hours you are asleep or the house is empty, for example from 19 degrees down to around 16 or 17 degrees overnight. The pump keeps running gently through the set-back period, so the house never gets cold and the pump never has to work flat out to recover. If your system has weather compensation, sometimes called the heating curve, leave it enabled so the pump automatically lowers its flow temperature on milder days.

Do not combine a set-back with switching the system off as well. The point of the set-back is that the pump stays on. Turning the heating off entirely and then expecting the pump to reheat the house from cold each morning is exactly the on-off pattern the Trust advises against.

The recovery problem: why switching off costs you more

The intuitive argument for switching off is heat-loss physics: a cooler house loses heat more slowly, so you must be saving energy while the heating is off. That is true as far as it goes, and it is why the advice is correct for boilers. With a heat pump, the saving gets swallowed by what happens next.

When you switch a heat pump off overnight, the house cools down, and the pump then has to reheat it from cold at the very moment it is least efficient. The Energy Saving Trust explains the mechanism: “During winter, the air temperature can drop by 5 degrees or more overnight. This will reduce the heat pump’s efficiency because it has to work harder to heat water to a high temperature.” A deep overnight setback hands the pump its hardest job of the day at the coldest hour of the day, exactly when every degree of flow temperature costs the most.

That is why the Trust draws the line where it does: “If the temperature of your home drops by a few degrees, your heat pump has to work a lot harder to warm it again. So, it’s best to keep your heat pump on all the time, and let your ‘set-back’ maintain a lower temperature when you’re out or asleep.” A shallow set-back of a few degrees keeps the recovery small enough that the pump can handle it at low, efficient output. A deep setback, or switching off entirely, turns every morning into a recovery marathon.

There is one more honest caveat. The Energy Saving Trust does not publish a pound-figure saving for running a heat pump steadily versus switching it on and off, so be sceptical of any website that quotes you one for this specific comparison. The direction of the advice is clear and well grounded; the exact saving depends on your house, your tariff and your settings, which is why testing it yourself is worth doing. More on that below.

Is it cheaper to leave a heat pump running? The exceptions

The “leave it on” rule has exceptions. Here are the ones that matter.

You are away for several days

On holiday, nobody needs a warm house, and a shallow set-back is no longer the right tool. Drop the system to its frost protection setting, the minimum that stops pipes freezing, and leave it there. Do not switch the heat pump off entirely for days in winter; frost protection exists for a reason. When you return, raise the setpoint gradually rather than demanding full comfort temperature in one go.

You are on a time-of-use tariff

This is the biggest exception, and it comes straight from the Energy Saving Trust: “Make sure your heat pump isn’t trying to heat your hot water or the house overnight when outside air temperatures are significantly lower. That’s unless you’re using a time of use tariff when electricity is cheaper.” If your tariff makes overnight electricity cheap, running the pump overnight can be fine. If you are on a standard single-rate tariff, schedule the heavy work, especially hot water, for the cheapest or at least the mildest part of the day. Our troubleshooting guide on why your bill is so high with a heat pump covers tariff choice in detail, because the tariff is often the single biggest lever on the bill.

Your hot water is scheduled badly

Leaving the space heating on gently is one thing; heating a full cylinder of hot water at 3am in deep cold is another. The Trust advises scheduling hot water for the cheapest time of day on your tariff. And check the legionella cycle: UK building regulations require cylinders to exceed 60 degrees regularly, and your heat pump may be set to do this daily. The Trust says that for most households, running the legionella function weekly is enough, and “if your bills are high, it may be because the timer has been set to do this job too frequently.” A daily legionella blast you do not need is a quiet bill inflator.

Your house loses heat very fast

Steady, low-and-slow heating works best in a house that holds its temperature. In a draughty, poorly insulated home, the pump has to work harder to maintain even a set-back temperature, and the whole strategy gets more expensive. If that sounds like your house, the insulation is the fix, not the heating pattern. Check who qualifies for free insulation grants in the UK, because loft and wall insulation is what makes low-temperature heating affordable in the first place.

Your heating curve is set too high

A heat pump left running all day with the heating curve set far too high will still cost more than it should, because it is doing the steady running at unnecessarily high flow temperatures. The Trust warns that a wrongly set curve increases running costs and that installers sometimes set it high just to be safe. Turn the curve down in one-degree increments through the winter; when the house starts to feel too cool, put it back up one degree and leave it there. Lowering the flow temperature, the Trust says, “will also have a big impact on your running costs.” Our winter checklist on boiler flow temperature and radiator checks covers the flow-temperature side of this in more depth.

How to test it on your own home

If you want proof rather than advice, run the experiment Money Saving Expert suggests. The site is admirably honest about the limits of generic guidance: “We wish we could give you a definitive answer, but this question is far more complex than it first seems and we’re not heating engineers or physicists.” Its proposed test is simple: run a week with the heating on a constant low setting with a set-back, then run a comparable week with the heating coming on only when you need it, taking meter readings at the start and end of each period, and compare the energy use.

Two conditions for a fair test. First, compare weeks with similar outdoor temperatures, because a cold snap will swamp any difference in heating pattern. Second, keep the hot water schedule identical across both weeks, since hot water is a large, separate load that can distort the comparison. If you try this, the Energy Saving Trust’s position is the stronger starting hypothesis: steady running with a set-back should come out cheaper for a heat pump, and by a wider margin the colder it gets.

Frequently asked questions

Is it cheaper to leave a heat pump on all day or use a timer?

Is it cheaper to leave a heat pump running than to use a timer? For a heat pump, generally yes: leaving it on all day at a steady, low temperature with a set-back is cheaper than timer-style on-off bursts. The Energy Saving Trust says heat pumps work best when left running all day, and that longer running does not raise overall costs because the efficiency gain offsets the longer running period. For a gas boiler the advice is the opposite: timer on-off is cheaper.

What temperature should I set the set-back to?

Lower the room temperature by a few degrees below your comfort setting when you are asleep or out, for example from 19 degrees to around 16 or 17 degrees. The Energy Saving Trust recommends the “a few degrees” set-back rather than a deep one, because if the house drops too far, the pump has to work much harder to warm it again.

Should I turn my heat pump off when I go on holiday?

Do not switch it off entirely in winter. Drop it to its frost protection setting so the house stays above freezing, and raise the temperature back gradually when you return. The “leave it on” guidance is for homes that are lived in; an empty house for a week needs frost protection, not comfort heating.

Does leaving a heat pump on all day use more electricity?

It uses electricity for more hours, but at much lower power and higher efficiency. The Energy Saving Trust is explicit that this trade-off works in your favour: “Leaving the heat pump on for longer periods can help too. This doesn’t increase your overall running costs because the heat pump can run more efficiently, offsetting the longer running period.” What raises electricity use is high flow temperatures and bad scheduling, not long gentle running.

Why is my heat pump running constantly? Is that normal?

Often, yes. A heat pump running quietly and continuously at low output is doing exactly what it was designed to do, and it is at its most efficient in that state. It becomes a problem only if the house never reaches the set temperature, the radiators stay stone cold, or the immersion or boost heater is running all the time. In that case the issue is usually the heating curve, radiator sizing or insulation rather than the running pattern itself.

Is it cheaper to leave the heating on low all day with a gas boiler?

No. The Energy Saving Trust says that with a boiler, keeping the heating on all the time uses more energy and costs more money; it is more efficient and better for your bills to have the boiler come on when you need it. The “leave it on” advice applies to heat pumps, not boilers, which is where much of the confusion comes from.

Sources

• Energy Saving Trust, “The most efficient way to run a heat pump” (updated 19 May 2026, re-verified 20 Oct 2026): energysavingtrust.org.uk/how-to-ensure-a-heat-pump-runs-efficiently
• Energy Saving Trust, “When should I put my heating on?” (blog post, 28 September 2026, re-verified 20 Oct 2026): energysavingtrust.org.uk/when-to-put-heating-on
• Money Saving Expert, via Brit Brief, “Martin Lewis MSE settles heating on all day debate” (3 October 2026): britbrief.co.uk/business/consumers/martin-lewis-mse-settles-heating-on-all-day-debate