The quickest way to make a heat pump more efficient is to lower its flow temperature to the minimum that still keeps your home warm, and then leave it running steadily instead of switching it on and off. Most of the other gains come from small settings changes and simple checks you can do yourself: opening radiator valves, cutting back the legionella cycle, heating water at the right time and keeping the outdoor unit clear.
Many systems are handed over with cautious settings that keep the house warm on the coldest day but waste energy the rest of the year. This guide covers what to change, what to check and how to tell whether it is working.
How Much Difference Does a Lower Flow Temperature Make?
A lower flow temperature makes a big difference: Kensa, a UK heat pump manufacturer, puts the efficiency loss at around 2% for every 1°C rise in flow temperature. On that rule of thumb, bringing your flow temperature down from 45°C to 40°C on a typical day would improve efficiency by roughly 10%.
Real-world data points the same way. A 2025 study in the journal Energy and Buildings compared UK homes on the open HeatPumpMonitor.org database with the government-funded Electrification of Heat trial. It found that systems achieving a seasonal performance factor (SPF) of 4.0 ran at average flow temperatures of about 36.6°C on the coldest days, while those at 3.5 averaged about 39.5°C.
The MCS Heat Emitter Guide uses star ratings to show how flow temperature relates to efficiency. It is a useful yardstick when you are deciding how low to push your settings.
| Design flow temperature | MCS Heat Emitter Guide rating | What it means for you |
|---|---|---|
| 35°C or below | 6 stars | Best efficiency; usually underfloor heating or generously sized radiators |
| 36–40°C | 5 stars | Very good; common target for well-designed radiator systems |
| 41–45°C | 4 stars | Good; typical of many retrofits |
| Up to 55°C | Part L limit | New and replacement wet systems in England must be designed for a maximum of 55°C flow |
Your radiators and insulation set the limit. The aim is the lowest setting that still keeps every room warm.
How Do I Tune My Weather Compensation Curve?
Tune the weather compensation curve by lowering it one step at a time, waiting a few days to see whether the house stays warm, and stopping one step before rooms start to feel cool. The Energy Saving Trust recommends lowering it a degree at a time and notes that installers sometimes set the curve high to make sure the house is warm in winter.
Weather compensation raises the flow temperature as it gets colder outside and lowers it as it gets milder. The curve, sometimes called the heating curve or slope, decides how steep that relationship is. A curve set too high means the heat pump runs hotter than needed on every mild day.
The 2025 Energy and Buildings study found that 55% of the Vaillant systems in the Electrification of Heat trial had their weather compensation set too high. Those systems averaged an SPF of 2.69, against 3.3 for better-configured systems.
A simple routine that works on most controllers:
- Note your current curve setting and the flow temperature shown on the controller, so you can go back if needed.
- Lower the curve by one step, or the flow temperature at design conditions by 1°C.
- Leave it for two or three days. The house responds slowly, so changing things daily gives confusing results.
- If every room still reaches your target temperature, repeat. If the house feels cool on colder days, go back one step.
- Recheck in the first properly cold spell, since a setting that works in October may fall short in January.
Should I Leave My Heat Pump On All the Time?
Yes, for most homes a heat pump is more efficient left running steadily with a small setback than switched off and on again. The Energy Saving Trust advises lowering the temperature by a few degrees overnight or while you are out, instead of turning the heating off.
When a house cools right down, the heat pump has to recover it quickly, which means a higher flow temperature and a harder-working compressor. Vaillant’s aroTHERM Plus handover guide makes the same point and suggests a setback temperature typically 3–4°C below your comfort temperature. The 2025 study also found underperforming systems cycling on and off, with long off periods of around 1.5 hours between high-temperature bursts.
In practice:
- Set one comfort temperature and a modest setback instead of on/off timer blocks.
- Avoid turning the room thermostat up to “catch up” after a setback, since the extra heat usually comes at a higher flow temperature.
- If the heat pump starts and stops many times an hour in mild weather, mention it at your next service. The flow temperature, minimum run time or system volume may need adjusting.
Should I Open My Radiator Valves Fully?
In most heat pump homes you should open the thermostatic radiator valves (TRVs) fully in the main living areas and let the heat pump’s controls set the temperature. Heat pumps rely on steady flow through the whole system, and TRVs closing down across the house reduce that flow and push the system to run less efficiently.
Some sensible exceptions apply. Bedrooms you like cooler can have TRVs turned down a little, and a room that overheats from sunshine may need one. The key is to avoid a house full of half-closed valves fighting the heat pump’s controls.
Does Bleeding and Balancing Radiators Help?
Yes, bleeding and balancing radiators helps because air pockets and uneven flow leave parts of the system cold, which tempts you to raise the flow temperature. Bleed any radiator that is cold at the top. Balancing, which means adjusting the lockshield valves so each radiator gets its share of flow, is best left to an engineer, but it is worth asking for if some rooms heat far more slowly than others.
How Should I Set Up Hot Water for Best Efficiency?
Set the cylinder to the lowest temperature that gives enough hot water, heat it once or twice a day at set times, and run the legionella cycle weekly rather than daily. Vaillant’s guide suggests storing water at 50–55°C, and many installers set lower where the household allows.
Hot water is the least efficient job a heat pump does because it has to reach a higher temperature than space heating. A few settings make a real difference:
- Temperature: drop the setpoint a couple of degrees at a time until you notice a shortfall, then go back one step.
- Timing: heat water in scheduled windows rather than whenever the cylinder cools slightly. Heating in the warmer afternoon, or in a cheap tariff period, usually suits a heat pump.
- Legionella cycle: the Energy Saving Trust says weekly is safe for most homes, and daily is unnecessary if you use hot water regularly. The cycle heats the store above 60°C, often with the immersion heater.
- Boost and backup heaters: check that any immersion or backup heater is not set to switch on routinely. The Energy Saving Trust advises using boost only when outdoor temperatures drop well below normal.
The table below shows why legionella cycle frequency matters. It is an illustration for a 200 litre cylinder lifted from 50°C to 60°C by the immersion heater, at the Ofgem price cap unit rate of 26.32p per kWh for October to December 2026. It ignores standing heat losses, so real costs will be a bit higher.
| Legionella cycle frequency | Cycles per year | Energy per cycle | Approximate yearly cost |
|---|---|---|---|
| Daily | 365 | About 2.3 kWh | About £223 |
| Twice a week | 104 | About 2.3 kWh | About £64 |
| Weekly | 52 | About 2.3 kWh | About £32 |
Can a Time-of-Use Tariff Cut My Heat Pump Running Costs?
Yes, a time-of-use tariff can cut running costs if you shift hot water heating and some space heating into the cheap periods. The Energy Saving Trust says switching to a heat pump time-of-use tariff should help reduce the cost of running a heat pump.
Octopus Energy’s Cosy tariff is one example built for heat pumps. It has three cheaper periods each day, 04:00–07:00, 13:00–16:00 and 22:00–00:00, priced 51% below the regional day rate, and a peak period from 16:00 to 19:00 priced 50% above it. It needs a smart meter that sends half-hourly readings. Terms change, so check the current details before switching.
For comparison, the Ofgem price cap from 1 October to 31 December 2026 is 26.32p per kWh for electricity on direct debit, with a standing charge of 54.83p per day. Ofgem states there is no VAT on domestic electricity from 1 October 2026 to 31 March 2027.
To get the most from a tariff like this:
- Schedule the cylinder to heat in a cheap window.
- Consider a slightly higher room temperature in the cheap period before the peak, then a small setback during the peak. Keep the difference modest so the heat pump does not have to work hard to recover.
- If you have solar panels or a home battery, use them to cover the peak period.
What Simple Checks Can I Do Myself?
You can check the outdoor unit is clear, keep an eye on the system pressure and read the controller for fault warnings, all without tools. Anything inside the unit or the refrigerant circuit is a job for an engineer.
| Check | How often | What to look for | Who does it |
|---|---|---|---|
| Outdoor unit | Monthly, more often in autumn and winter | Leaves, snow, plants or stored items blocking airflow | You |
| System pressure | Monthly | Typically 1–1.5 bar when cold on many systems; check your manual | You (top up only if shown how) |
| Controller fault log | Monthly | Repeated warnings or error codes | You, then your installer |
| Radiators | Start of the heating season | Cold at the top (air) or cold at the bottom (sludge) | You for bleeding; engineer for sludge |
| Filter and strainer | At the annual service | Debris restricting water flow | Engineer |
Vaillant’s handover guide asks owners to keep the area around the unit free of clutter and to check it in autumn and winter, since leaves or snow build-up affect how it runs. For Daikin systems, Octopus’s support guide says pressure should be 1–1.5 bar when the system is cold and should be topped up via the filling loop if it drops below 1 bar. Other brands vary, so use your own manual’s figures.
The Energy Saving Trust also recommends dealing with faults straight away and contacting the manufacturer about recurring warnings.
Will Insulation and Draught-Proofing Make My Heat Pump More Efficient?
Yes, insulation and draught-proofing make a heat pump more efficient because a home that loses less heat can be kept warm at a lower flow temperature. The heat pump then works in its more efficient range for more of the year.
After any insulation work, revisit your weather compensation curve, since it was set for the old heat loss. The cheapest fixes are often the simplest: draught-proofing doors and windows, sealing gaps around pipes and loft hatches, and topping up loft insulation. Larger jobs such as cavity or solid wall insulation cost more but can allow a noticeably lower flow temperature.
Radiators matter too. The Energy Saving Trust points out that at the 45°C typical of heat pumps, radiators sized for a boiler may not be big enough. Swapping one or two undersized radiators in the coldest rooms can let you lower the curve for the whole house.
How Do I Know If My Heat Pump Is Running Efficiently?
You know your heat pump is running efficiently by working out its seasonal performance factor: the heat delivered over a period divided by the electricity used. Many heat pumps display both figures on the controller or app, and some installs include a separate heat meter and electricity meter for more accurate readings.
The Electrification of Heat trial, which monitored 742 heat pumps in British homes, found a median SPF of 2.80. The 2025 Energy and Buildings study found an average SPF of 3.86 among the systems listed on HeatPumpMonitor.org, which tend to be well set up and closely watched by their owners.
| Seasonal performance factor | Electricity for 12,000 kWh of heat | Approximate cost at 26.32p/kWh |
|---|---|---|
| 2.8 | About 4,290 kWh | About £1,128 |
| 3.0 | 4,000 kWh | About £1,053 |
| 3.5 | About 3,430 kWh | About £902 |
| 4.0 | 3,000 kWh | About £790 |
The table is illustrative, for a home needing 12,000 kWh of heat and hot water a year, and excludes the standing charge. It shows that moving from 2.8 to 3.5 would save around £225 a year at current cap prices.
Take a reading on the first of each month and compare the same months year on year, since a mild winter flatters the figures. A sudden drop with no change in weather is worth raising with your installer.
Does an Annual Service Keep a Heat Pump Efficient?
Yes, an annual service keeps a heat pump efficient by catching the slow problems that owners cannot see, such as a partly blocked strainer, low pressure in the expansion vessel or a sensor reading incorrectly. Vaillant’s handover guide lists annual servicing among its efficiency tips.
Use the visit to ask the engineer to review your settings as well as the hardware. A look at the weather compensation curve, hot water schedule and legionella cycle alongside your SPF readings can find savings the mechanical checks miss. If you have an unvented cylinder, ask for its annual safety check at the same time.
If your heat pump is costing more than you expected and you would like our engineers to look at the settings, get in touch to arrange a visit.
