Why Is My Heat Pump Expensive to Run? A Five-Point Diagnostic Checklist

Quick answer: High heat pump running costs almost always trace back to five things: flow temperature set too high, weather compensation switched off, short cycling, the wrong electricity tariff, or a badly sized unit. At the October–December 2026 price cap of 26.32p/kWh, a well-set-up system in a typical three-bed home costs roughly £900 a year to run — if yours costs far more, work through the checklist below.

First: is it actually expensive?

Before changing any settings, put a number on the problem. A heat pump’s running cost is simply the heat your home needs divided by the system’s seasonal efficiency (SCOP), multiplied by your electricity price. As an illustration, take a home that needs 12,000 kWh of heat a year — a reasonable figure for a typical three-bed semi — and the October–December 2026 price cap rate of 26.32p/kWh:

The gap between a poorly set-up system and a well-tuned one is around £350 a year on the same house — which is why settings matter more than the badge on the unit. Our guide to how much electricity a heat pump uses per year explains how to read your own consumption from a smart meter, and our COP explainer covers what drives the efficiency number.

Check 1: flow temperature (the biggest lever)

The single most common cause of expensive running is a flow temperature set too high — often left at 50–55°C after installation. Heat pumps get dramatically more efficient as the water they send to your radiators gets cooler: as a rough engineering rule, every 1°C you shave off the flow temperature cuts electricity use by around 2–3%. Many homes can run at 40–45°C or lower with the radiators they already have. Our guide to heat pump flow temperatures and radiators shows how to test a lower setting safely over a few days.

Check 2: weather compensation

Weather compensation adjusts the flow temperature automatically as the outdoor temperature changes, so the system only works as hard as the weather demands. It is the difference between a heat pump that sips electricity in mild weather and one that runs flat out all year. If your unit is running at a fixed flow temperature, this is usually free money: see how to set a weather compensation curve for a step-by-step walkthrough.

Check 3: short cycling

A healthy heat pump runs in long, steady stretches at low output. If yours starts and stops every few minutes — you can usually see run-time and start counts in the controller or app — it is short cycling, which wastes electricity and wears the compressor. Oversized units and systems with too little water volume are the usual culprits. Our guide to heat pump short cycling covers the causes and fixes in detail.

Check 4: your electricity tariff

Every kWh a heat pump uses is charged at your electricity rate, so the tariff matters as much as the hardware. The October–December 2026 price cap averages 26.32p/kWh across GB, but several suppliers now offer heat-pump-specific or time-of-use tariffs with cheaper rates for some or all of the day. If you have been on a standard variable tariff since the pump went in, comparing tariffs is often the quickest saving available — no tools required.

Check 5: sizing

A unit that is too big for the house will short cycle in mild weather and cost more to run; one that is too small leans on its backup immersion heater in cold snaps, which runs at plain electric-heater efficiency. If your system has either symptom, dig out the heat-loss calculation from your installation paperwork. Our guides to oversizing problems and what size heat pump different properties need explain how to sanity-check the numbers.

Two things that look expensive but are normal

• Defrost cycles. On cold, damp days the outdoor unit periodically melts frost off its coil, and consumption spikes briefly. This is normal — see how the defrost cycle works.
• The weekly hot water sterilisation. Once a week the cylinder is heated to 60°C to control Legionella bacteria, usually with the immersion heater. It typically costs well under £1 a week — our Legionella cycle guide has the exact numbers.

Still expensive after all five checks?

If consumption stays stubbornly high after tuning the settings, suspect a fault rather than a setting: a blocked filter, failing sensor, refrigerant issue or a backup heater that has quietly taken over. Check the controller for stored fault codes (our error code guide explains the common categories), run through our troubleshooting guide, and book an annual service if the unit hasn’t had one. To see how your running costs compare with other heating systems for your home, try our cost calculator or read our full heat pump guide.

FAQs

What should a heat pump cost to run per day?

It varies hugely with weather and house size, but as a yardstick: a home needing 12,000 kWh of heat a year with a SCOP of 3.5 averages around £2.47 a day at the October–December 2026 cap rate — much less in summer, several times that in a cold January week.

Which single setting saves the most money?

Flow temperature, almost always. Dropping from 50°C to 40°C can cut electricity use by roughly 20–30% on the rule-of-thumb figures above, provided your radiators can still heat the rooms at the lower temperature.

Is it cheaper to leave a heat pump on all the time?

Usually yes — heat pumps are most efficient running low and slow for long periods rather than blasting on and off to a timer. Weather compensation plus a modest overnight setback (1–2°C) suits most homes better than switching the system off completely.