Heat Pump Running Costs Too High — How to Reduce Them
Heat pumps are highly efficient when set up and running correctly, but a surprising number of installations end up costing more to run than expected. If your electricity bills have shot up since your heat pump was installed, you're not alone — and the good news is that the problem is usually fixable without calling out an engineer. Most cases boil down to a handful of settings that either weren't optimised during commissioning or have drifted out of tune over time. This guide walks you through the main culprits: flow temperature, immersion heater use, weather compensation, and tariff choices. Many homeowners can sort these issues themselves in under an hour. If you've worked through these steps and efficiency is still poor, that's the time to bring in an MCS-accredited engineer to check the refrigerant charge and system performance.
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Most likely cause & what to check
Heat pumps should achieve a Coefficient of Performance (COP) of 2.5–4.0 — meaning for every 1 unit of electricity used, you get 2.5 to 4 units of heat. If your bills seem disproportionately high, the system may not be running efficiently. Check your heat pump controller for a COP or SCOP reading if it has one.
Check the flow temperature — the single biggest factor in heat pump efficiency. Every 1°C reduction in flow temperature improves efficiency by around 2–3%. If your system is set to run at 55°C when 45°C would heat the house adequately, you are paying significantly more than necessary. Ask your installer to review the settings.
Check for an immersion heater running unnecessarily — many heat pump systems include an electric immersion heater as a backup for hot water or as a legionella protection top-up. If the immersion is running daily rather than once a week, it will dominate your electricity bill. Check the cylinder settings.
Check weather compensation is enabled — weather compensation automatically lowers the flow temperature on mild days and raises it on cold days. Running at a fixed high flow temperature in mild weather is inefficient. Most heat pump controllers have weather compensation as an option that may need enabling.
Check your electricity tariff — heat pumps run best on a time-of-use tariff (such as Octopus Agile or Economy 7) that charges less at off-peak times. The heat pump can be programmed to pre-heat the home overnight at cheap-rate electricity.
If efficiency is still poor after reviewing settings, an MCS engineer should check the refrigerant charge and system performance — a heat pump running with low refrigerant will have a poor COP and higher running costs.
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Frequently asked questions
What is a normal COP for a heat pump, and why does it matter?
A healthy heat pump should achieve a COP (Coefficient of Performance) of 2.5–4.0, meaning you get 2.5 to 4 units of heat for every 1 unit of electricity consumed. If your system is delivering less, you're paying more per unit of heat than you should be. Check your controller's display or logbook for a COP or SCOP reading to see how your system is actually performing.
How much does lowering the flow temperature actually save?
Every 1°C reduction in flow temperature improves efficiency by roughly 2–3%. If your system is running at 55°C when 45°C would adequately heat your home, you could be looking at 20–30% higher running costs than necessary. Lower flow temperatures also reduce strain on the system and extend its lifespan.
Why is my immersion heater running so often?
Immersion heaters are often set to run daily as a legionella protection top-up or to boost hot water on demand, but this can add £20–40 per month to your bill. Check your cylinder thermostat settings — most systems only need the immersion to run once a week, or only on very cold days when the heat pump alone can't keep up.
What's the best electricity tariff for a heat pump?
Time-of-use tariffs (such as Economy 7 or Octopus Agile) are ideal for heat pumps because you can programme the system to pre-heat your home and hot water tank during off-peak hours when electricity is cheapest. A standard flat-rate tariff may work, but you'll miss out on significant savings if your heat pump has a smart controller capable of scheduling.