Why Is My Heat Pump So Expensive to Run?

Why Is My Heat Pump So Expensive to Run?

If your heat pump is costing far more to run than you expected, you are definitely not alone. One of the biggest frustrations UK homeowners face is being told their heat pump should be cheap to run only to find themselves with unexpectedly high electricity bills month after month. The important thing to understand is that a heat pump running expensively is almost always a symptom of something else going on within the system, not an inherent flaw in heat pump technology itself. In most cases, there is a reason for it and in many cases, it can be improved significantly.

Heat pumps themselves are not inherently expensive to run. When designed and set up correctly for the property they serve, they can be highly efficient and genuinely cost-effective compared to gas heating. The problem is almost always rooted in system design, setup, controls, flow temperatures, heat loss, or the way the home is being heated. That is why two identical heat pumps installed in two different homes can produce completely different running costs the unit is the same, but everything around it is different.

1. Flow temperatures are too high. This is one of the single biggest causes of high heat pump running costs in the UK. Heat pumps are most efficient when operating at lower flow temperatures typically 35–45°C under normal winter conditions. When a system is running at 55°C, 60°C, or higher on a regular basis, it uses considerably more electricity to produce the same amount of heat. This often happens because radiators are too small to deliver enough heat at lower temperatures, controls have not been set correctly, or the system is compensating for another underlying problem elsewhere. Understanding what flow temperature your heat pump should run at is one of the most important steps in reducing running costs, and it is something we look at in detail during every diagnostic review.

2. The property loses heat too quickly. If a home has high heat loss through poorly insulated walls, draughts, older single-glazed windows, open fireplaces, or uninsulated pipework the heat pump has to work much harder and run for much longer to maintain the target temperature. This directly increases electricity consumption. Heat pumps can work well in older and less efficient properties, but only when the system has been properly designed around the actual heat loss of that specific home. If yours was not, running costs will reflect that mismatch. Our article on why your house is still cold with a heat pump explores this in more detail and covers what to check first.

3. The heat pump is incorrectly sized. Sizing matters more than many homeowners realise and more than many installers acknowledge. An undersized heat pump will run constantly, struggle to heat the house properly, and operate inefficiently because it is always working at or beyond its design limits. An oversized heat pump will short-cycle constantly starting and stopping which also reduces efficiency and increases wear. Both scenarios lead to higher running costs than a correctly sized system would produce. If you suspect sizing may be the issue, our guide on what size heat pump your house needs walks through how correct sizing is calculated and what happens when it goes wrong.

4. Poor system balancing or circulation problems. Even when the heat pump itself is working perfectly, the system can still perform badly if heat is not moving properly around the property. Common issues include poor radiator balancing, low flow rates through the system, blocked strainers, incorrect circulation pump settings, or zoning problems that prevent heat from reaching certain areas. These issues often lead to uneven heating across the home, which in turn pushes flow temperatures higher as the system tries to compensate, increasing electricity use further. Our article on why some heat pump systems struggle to circulate through radiators explains the most common causes and how they are identified. System balancing is a fundamental part of heat pump setup and is covered in depth in our heat pump system balancing explained guide.

5. Incorrect controls or thermostat settings. A large number of heat pump systems in the UK are simply not configured correctly. Aggressive setback temperatures where the system drops to a very low temperature overnight and then has to recover — force the heat pump to work harder than if it had maintained a steady temperature throughout. Incorrect weather compensation settings, timers that conflict with each other, or thermostats that shut zones off too early all increase running costs in ways that are not immediately obvious to the homeowner. Our guide on best heat pump thermostat settings for UK homes covers the most important settings to check and how to set them correctly.

6. Frequent defrost cycles or short cycling. If your heat pump is defrosting very frequently or starting and stopping in short bursts, efficiency suffers significantly. Frequent defrost cycles can be caused by poor airflow around the outdoor unit, control issues, or system design problems that cause the unit to operate in conditions it struggles to manage. Short cycling is often a sign of oversizing or a system volume problem. Both issues are covered in our article on why your heat pump defrosts so often and are something we look at specifically during a full performance review.

7. The system was never properly commissioned. This is more common than most homeowners realise, and it is one of the most frustrating causes of high running costs because the problem exists from day one. Incorrect flow rates, wrong controller settings, poorly configured weather compensation, incorrect pump settings, or refrigerant issues left over from installation can all affect efficiency significantly and permanently unless they are identified and corrected. Our guide on common commissioning mistakes with air source heat pumps is essential reading if you have never had your system properly checked since installation.

Do Heat Pumps Actually Save Money?

Yes they genuinely can, and for many UK homeowners they do. But only when the system is designed correctly for the property, controls are configured properly, flow temperatures are kept at appropriate levels, and the home's heat loss has been properly understood and accounted for. When those things are right, heat pump running costs can be very competitive compared to gas heating particularly with an off-peak electricity tariff. When they are wrong, electricity bills can be surprisingly high. Our honest UK guide to heat pump running costs versus fossil fuels gives a clear picture of what realistic savings look like and what conditions are needed to achieve them.

The Key Thing Most People Miss

Most heat pumps that are expensive to run are not broken. They are usually poorly configured, compensating for another issue in the system or the property, or simply not matched properly to the home they are heating. That is why randomly adjusting settings turning flow temperatures up or down, changing timer schedules, or switching weather compensation on and off without understanding what it does often makes things worse rather than better. The system needs to be understood properly before changes are made. Our article on how to set a heat pump for maximum efficiency is a good starting point if you want to work through the settings yourself.

Can High Running Costs Be Fixed?

In many cases, yes. Sometimes the fix is straightforward settings, balancing, controls, or flow temperature adjustments that can be made without any physical work on the system. Other times the issue is more fundamental, involving system design or the property itself. But the most important point is this: high running costs are almost always a symptom of something else, not the root problem. Identifying the root cause is what leads to a genuine, lasting improvement rather than a temporary change that makes no real difference to the electricity bill. Our guide on how to reduce heat pump electricity bills covers the practical steps in detail.

If you need help understanding exactly why your heat pump is costing so much to run, our Full Performance Review looks at flow temperatures, controls, system behaviour, cycling, balancing, heat loss, and setup and in many cases we can identify the issue during the call itself. If you are still at the planning stage, our Pre-Installation Design and Heat Loss Review ensures the system is designed correctly from the outset, so expensive running costs never become a problem in the first place.