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Should you leave your heat pump running or time it like a boiler? A Heat Geek engineer explains temperature, weather compensation and timers for Scottish homes.
Sean Hogan · Heat Geek engineer · Updated September 2026 · 7 min read
Most people who have just had a heat pump fitted make the same mistake in the first winter: they run it like the boiler it replaced. A boiler likes short bursts, blasting a room from cold in twenty minutes, then sitting quiet until the next timed slot. A heat pump works the opposite way. It is built to hold a steady, low-level heat for hours at a time, and treating it like a boiler is the single biggest reason a new heat pump owner ends up unhappy with their first bill.
Short answer: leave it running through the heating season at a steady room target, let weather compensation handle the flow temperature as conditions change, and only step in to adjust the schedule itself if your household’s actual pattern of being home changes. The rest of this guide covers what each of those settings actually means and why.
A boiler heats water fast and expensively, so the cheapest way to run one has always been short bursts: on for an hour in the morning, off all day, on again in the evening. A heat pump moves heat rather than burning gas to make it, and it is most efficient producing a low, steady flow temperature over a long period. Switching it on and off like a boiler forces it to work harder to recover the temperature each time, which is the opposite of what you paid for.
The practical difference shows up in how the house feels. A boiler heats a room quickly and lets it cool between cycles. A heat pump holds the whole property at a gentle, constant warmth, with radiators running cooler for longer. If your radiators feel barely warm to the touch and the house is still comfortable, that is correct behaviour, not a fault.
We cover the full mechanics of how a heat pump actually produces that heat, compressor cycle, refrigerant, flow temperature, in our Scotland heat pump guide. This article deals specifically with what you set day to day once the system is running.
Yes, for almost every Scottish home. A heat pump sized correctly for your property’s heat loss is designed to run near-continuously through the heating season, holding the building at a set temperature rather than chasing it back up after long gaps. Turning it off overnight and back on at 6am asks the system to reheat a cold building from scratch, which takes longer and costs more than simply maintaining the temperature through the night.
This is the question we get asked most by new clients in their first few weeks. The habit of switching off an empty house is a boiler habit, built around fast, expensive heat. A heat pump’s running cost comes from how much heat the building loses, not from how many hours the unit is switched on, so leaving it running at a steady background temperature almost always beats cycling it hard.
The exception is a property standing empty for several days: a holiday let between bookings, or a second home. There, a lower setback temperature, not off, protects the fabric and the pipework without wasting heat on an empty building.
We will check how your heat pump is actually set against how your household lives, and tell you straight if anything needs changing.
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There is no single correct number. Flow temperature, the temperature of the water leaving the heat pump and going to your radiators or underfloor loops, depends on how much heat your radiators can give off and how much heat your house loses. A well-insulated new build might run comfortably at 35°C flow. An older stone-built property with the original radiators often needs 45 to 50°C to keep the same rooms warm.
This is decided at the survey stage, room by room, against a heat loss calculation, not guessed after installation. Radiator sizing and flow temperature are the same conversation: undersized radiators force a higher flow temperature, which costs more to run. Getting that right before the system goes in is worth more to your bill than any setting you will touch afterwards.
Room thermostat targets are a separate figure from flow temperature, usually 19 to 21°C for a living space and cooler in bedrooms. Set the room target once, sensibly, and leave it. Chasing it up and down through the day undoes the steady-state efficiency the whole system is built around.
Weather compensation is the setting that actually answers the question in this guide’s title without you touching anything again. An outdoor sensor tells the system how cold it is, and the controller automatically raises or lowers the flow temperature along a curve you set once: colder outside means a higher flow temperature, milder days mean a lower one.
The result is a house that stays at a constant comfortable temperature without you adjusting anything as the weather changes. Most of the manual fiddling homeowners do with a new heat pump, turning it up on a cold snap, down on a mild afternoon, is work weather compensation already does automatically once the curve is set correctly for your property.
We set this curve during commissioning, based on your home’s heat loss and radiator output, and it is the one setting worth understanding even if you never touch anything else. Get the curve wrong and the system either undershoots on cold days or wastes energy overshooting on mild ones.
A £0 survey puts real numbers against your property: flow temperature, weather compensation curve and what it would cost to run correctly.
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Scotland’s heating season runs long, typically from late September through to April in most properties, longer again in an older stone-built house with harder-to-heat rooms. The heat pump should stay active through that whole stretch rather than being switched off in the milder months and back on at the first cold snap.
Summer is different only for hot water, not space heating. Once the heating itself is off for the season, the heat pump switches to running the hot water cylinder alone, which draws far less than heating the whole house and is a small, predictable running cost through summer.
How your system performs through a proper Scottish winter, not a mild southern one, is covered in detail in our piece on heat pump efficiency in Scottish winters. The short version is that a correctly set weather compensation curve does most of the seasonal adjusting for you.
The one manual change worth making each year is confirming the heating on and off dates match how your household actually uses the house, not a generic calendar. A cold, exposed property might need the system live a few weeks earlier than a sheltered one nearby.
Every heat pump we install comes with an app, Panasonic’s Aquarea Smart Cloud, Vaillant’s myVAILLANT, or the equivalent for Samsung and other systems, that shows flow temperature, hot water status, and lets you adjust the schedule from your phone. It is useful for checking the system is behaving, less useful as a tool for aggressive on and off scheduling.
Set the timer to match your household’s actual pattern, not a boiler-era default. A single wide “on” window covering the hours the house is occupied works better than several short slots trying to mimic old boiler habits. If you are not sure how to navigate the app itself, we cover that step by step in our separate guide to the manufacturer app in the Aventus Help Centre.
The wall-mounted controller does the same job as the app for day-to-day use. The app mainly adds remote access and a longer history of how the system has been running. Either is fine. What matters is that the schedule reflects when the house needs heat, not how the old boiler used to be run.
Most homes keep more radiators than they expect. The £0 survey checks every room, not a rule of thumb.
“We initially had Sean over to provide a quote, and as we didn’t know much about heat pumps, he explained everything clearly and in a way we could easily understand. He emphasized the importance of proper heat loss calculations for our property, which helped us determine which existing radiators we could keep.”
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The single biggest mistake is timing a heat pump like a boiler, covered above, and it alone accounts for most of the “my heat pump is expensive” complaints we hear. The second is setting the flow temperature higher than the property needs just in case, which increases running cost without making the house any warmer once the radiators are already meeting demand.
A third is ignoring the room thermostat entirely and running everything from the outdoor unit’s default settings, which skips the input that actually tells the system when to ease off. A fourth is switching the system off during a cold snap to save money, which is exactly when a heat pump is working hardest to hold the building’s temperature and least able to recover cheaply from a cold start.
If your bills do not match what a correctly set up heat pump should cost for a property like yours, the fix is rarely the thermostat. It is usually the settings underneath it: flow temperature, weather compensation curve, or a heat loss calculation that was never done properly at installation. Our heat pump running costs guide breaks down what a well set up system should actually cost to run in a Scottish home.
Yes, for most Scottish homes through the heating season. A heat pump is designed to hold a steady background temperature rather than being switched on and off like a boiler. Turning it off overnight and reheating a cold house each morning costs more than maintaining the temperature continuously.
It is an automatic setting that raises or lowers your flow temperature based on the outdoor temperature, using a curve set once during commissioning. Once it is configured correctly for your property, you should not need to adjust the temperature manually as the weather changes.
There is not one figure that suits every home. Flow temperature depends on your radiators and how much heat your property loses, typically 35°C in a well-insulated new build and 45 to 50°C in an older stone-built house with the original radiators. Room thermostats are usually set between 19 and 21°C.
Almost always, yes. A heat pump’s running cost is driven by how much heat your building loses, not by how many hours it is switched on. Leaving it running at a steady background temperature avoids the expensive reheat that comes with switching it off and on like a boiler.
Space heating usually switches off for the summer months once the weather no longer calls for it, and the system runs the hot water cylinder alone, a small, predictable cost. The heating schedule itself needs no manual seasonal adjustment if weather compensation is set correctly.
Flow temperature should be set as low as your radiators or underfloor loops can manage while still heating each room properly, decided against your specific heat loss and radiator sizing at survey stage rather than a generic figure. Our guide to radiator sizing explains how that number is worked out.
Every setting in this guide, flow temperature, weather compensation, the heating schedule itself, comes from the same starting point: an accurate heat loss calculation for your specific property. Guess it, and you are either overpaying to run the system or under-heating the rooms that need more.
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