Why does my heat pump run all the time?

You've had your heat pump installed, and you've noticed it seems to be running almost all the time. The old boiler fired up, warmed the house and switched off. This one just keeps going. It's a common worry, and the answer is reassuring: in most cases, a heat pump running for long stretches is doing exactly what it was designed to do.

The short answer

A heat pump is meant to run for long periods at a low, steady output, rather than in short, hot bursts like a boiler. Running continuously is how it keeps your home comfortable while using as little electricity as possible. It only becomes a sign of a problem when the pattern changes - when it switches on and off every few minutes, or runs flat out and still can't warm the house.

Low and slow: a different way of heating

A boiler makes heat by burning fuel, but a heat pump doesn't make heat at all; it moves heat that already exists in the outside air into your home. Because moving heat takes far less energy than creating it, a well-designed heat pump delivers around three to four units of warmth for every unit of electricity it uses. No boiler can come close to that.

But that efficiency depends on running gently. The smaller the gap between the outside air and the temperature of the water in your radiators, the less work the heat pump has to do. So instead of heating water to 70–80°C in short bursts like a boiler, it circulates cooler water, usually somewhere between 30°C and 50°C, around your radiators or underfloor heating over much longer periods. This is called low and slow heating, and it's the main reason a heat pump can be so efficient. A compressor running steadily at modest output does far less work for the same warmth than one that keeps accelerating to full power and stopping.

So when you see the unit outside running quietly for hours, it isn't struggling. It's ticking over at a fraction of its effort, keeping your home at a steady temperature. If it helps, think of a car on the motorway: cruising at a constant sixty uses far less fuel than repeatedly flooring it and braking. Your heat pump is built to cruise. There's more on the mechanics behind this in our guide to how heat pumps work.

Your home is part of the system

There's a second reason continuous running makes sense, and it's about your house, not the heat pump.

Every building has thermal mass: the ability of walls, floors, furniture and even the water in your heating system to soak up heat and release it slowly. As those materials warm through, they act like a large, slow battery, giving warmth back to the rooms over many hours. Homes with solid floors or underfloor heating have plenty of it. They take a while to warm up, but they hold that warmth beautifully.

A heat pump works with that thermal mass rather than against it. By topping up heat continuously, it keeps the whole house sitting at a steady temperature, so it never has to claw its way back from cold.

Why turning it off overnight usually backfires

This is the part that catches most new owners out. With a boiler, switching the heating off overnight or when you're out saved money. With a heat pump, it often does the reverse.

If you let the house go cold, the heat pump then has to replace all that lost heat at once, which usually forces it to run hotter and less efficiently to catch up. You spend more recovering the temperature than you'd have spent simply maintaining it. This is why most heat pumps are happiest left running through the heating season, nudged by their controls rather than switched on and off.

Many systems handle this automatically through weather compensation, which quietly adjusts the water temperature to match the weather (a little cooler on a mild day, a little warmer on a cold one) so your home gets just the heat it's losing at that moment, and no more. Instead of swinging between too warm and too cool, the house simply stays comfortable.

When constant running is worth a second look

Running steadily for hours is normal. Switching on and off every few minutes is not. That pattern is called short cycling, and it's a different thing entirely: the compressor starting, running briefly, stopping, then starting again, over and over.

Common culprits are too little water volume in the system, poor flow rates, an oversized heat pump, or thermostat settings fighting the controls. A good installer designs the system specifically to avoid short cycling, and on each annual service will check all of these factors to ensure your system is ticking over as it should. If it sounds like your system is short cycling, it's worth raising with your installer or getting a service.

A couple of related things you might have noticed

The radiators feel warm, not hot. That's by design. It isn't the temperature of the radiator surface that heats a room, it's the total warmth delivered over time. A radiator at 40°C running for hours puts more heat into a room than one at 70°C running for twenty minutes, then going cold. Warm radiators and a continuously comfortable home go together.

It runs more in cold weather. Also normal. The colder it is outside, the faster your home loses heat, so the harder any heating system works to keep up. A heat pump will run longer during a cold snap than on a mild autumn afternoon. Its efficiency does ease off a little in the cold, but even at freezing it stays well ahead of a boiler, and modern air source units are built to keep heating far below zero. They're used across Scandinavia, where winters are far harsher than ours.

The short version

Once you stop expecting the bursts of a boiler and let the heat pump do its steady, quiet job, the constant running stops feeling like a worry and starts making sense. Long, gentle running periods are the system working as intended: keeping your home evenly warm for as little electricity as the weather allows.

If you're weighing up a heat pump for the first time and want a sense of the numbers for your own home, our heat pump vs gas boiler guide is a good place to start. Or get an instant estimate in minutes — no survey, no obligation.