Common heat pump problems: high bills, cold rooms and fault symptoms

If a heat pump is not keeping the house comfortable or its electricity use seems unexpectedly high, start by recording the symptom and checking ordinary user settings. The cause may involve controls, hot-water operation, an emitter, the heating design or an equipment fault. A single symptom rarely identifies the answer on its own.

This guide helps you gather useful information and decide when to contact the installer. It does not replace the owner's manual or provide instructions for electrical, refrigerant or pressurised-system repairs. Reviewed 29 October 2026.

Start with the symptom

Symptom	Safe first checks	What to give the installer
Whole house cold	User schedule, room target, holiday mode and displayed messages	Actual room temperatures, times, outdoor conditions and fault code
One room cold	Ordinary room control, obstructions and whether the issue is new	Room, emitter, temperature difference and when it occurs
High electricity use	Actual readings, tariff, period covered and other household demand	Daily readings with weather and heating/hot-water context
Not enough hot water	User schedule, recent demand and any displayed warning	Cylinder details, usable supply and recovery pattern
Ice or visible vapour	Observe from a safe distance and check the manual's defrost explanation	Photographs, duration and whether heat returns normally
New noise or vibration	Note the timing and location without opening equipment	Recording, operating mode and any recent changes
Repeated fault	Record the exact code and follow the manual's advice	Model, code, frequency and previous attempts to resolve it

If equipment is smoking, sparking, leaking onto electrical parts or otherwise appears immediately unsafe, keep away and use the appropriate emergency or professional route. Ordinary troubleshooting should never involve removing covers or defeating a safety device.

The heat pump is running, but the house is cold

Check the intended room temperature and whether the heating schedule or holiday setting explains the operation. Identify any recent changes to settings, occupancy or the building. Keep a record before adjusting anything.

Distinguish a whole-house problem from one cold room. A local issue may involve the room's emitter, control or flow, while a wider problem may need review of settings, supply, heat demand or equipment performance.

Ask the installer to compare the actual conditions with the design. What indoor temperatures were promised, at what outdoor condition, and with what flow-temperature strategy? A homeowner should not be expected to accept persistent cold as an inherent requirement of heat-pump heating.

The radiators feel lukewarm

Touch temperature is not a reliable verdict. A radiator operating at a lower water temperature for longer can still provide the heat the room needs. Measure the room rather than judging only the metal surface.

If the room remains below the agreed target, record the temperature and timing and ask for an assessment against the emitter schedule. Increasing the temperature for the whole system can mask a particular room's problem without resolving its cause.

Do not close every other emitter in an attempt to force heat into one room, or change installer-only pump settings. The system may require minimum flow and a specific control strategy. See our radiator compatibility guide.

Illustrative image. The equipment and layout for a particular home must be assessed as part of its design.

Electricity use is higher than expected

First compare the right bills. Moving heating from gas or oil to electricity normally increases the electricity account's consumption. Compare the combined former fuel and electricity spending with the new total for a comparable period.

Check whether readings are actual or estimated, whether the tariff changed and whether an EV, electric heater or other household load accounts for part of the increase. A Direct Debit can reflect account balance rather than the equipment's current consumption.

Winter demand is not an annual average. Record weather, room temperatures, hot-water use and any backup-heater operation that the user display reports. Ask the installer to explain a persistent discrepancy from the predicted electricity use.

For a meaningful efficiency assessment, heat output and relevant electricity inputs need suitable measurement. A smart meter alone does not provide both. OpenEnergyMonitor explains monitoring boundaries, and our running-cost guide shows the arithmetic.

The outdoor unit is icing up

Air-source equipment can develop frost and periodically defrost. Vapour or water during a normal cycle can look concerning without being a fault. Follow the exact manufacturer's explanation for your model.

Mitsubishi Electric describes normal defrost behaviour in its cold-weather guidance. That is an example of how a manufacturer explains its equipment, not a diagnostic rule for every system.

Contact the installer if ice persists, the fan appears obstructed, drainage freezes in a way affecting operation, or heating fails to recover. Photograph the condition from a safe position. Do not chip ice, pour boiling water over the equipment or reach near the fan.

Hot water runs out or takes too long to recover

Record what the system supplied and the demand before it ran short: for example, consecutive showers or a bath followed by another shower. Check ordinary schedules and displayed warnings without changing safety or hygiene settings.

Ask whether the commissioned arrangement meets the household pattern agreed at survey. A storage issue, schedule issue and equipment fault need different responses. Record cylinder and heat-pump model details so the installer can investigate the right combination.

Do not disable required hygiene routines or increase temperatures beyond the owner's instructions to experiment. Our hot-water guide explains the design questions behind supply and recovery.

The system switches on and off frequently

Note how often this happens, the weather and whether rooms are reaching their targets. Frequent starting can have several causes; an online statement that every system should make a fixed number of starts per hour is not a diagnosis.

Ask the installer to review the operating data, controls and hydraulic design. Do not randomly change pump speed, buffer settings, valves or compensation curves. Those changes can interact and make the original problem harder to trace.

The Energy Saving Trust controls guidance explains why matching heat output and temperature to demand matters. It is not a universal set of homeowner adjustment instructions.

A new noise has appeared

Record whether it comes from the outdoor unit, pipework, pump or an emitter, and whether it occurs at startup, defrost or hot-water heating. A short recording and an operating-mode note can be more useful than simply reporting that the system is loud.

Do not lubricate components, remove covers or fit an enclosure yourself. Ask the installer to investigate new mechanical sounds, vibration or contact with surrounding materials. Screens and barriers also need assessment for airflow and access.

If the concern affects a neighbour, record the circumstances calmly and share them with the installer. Existing planning compliance does not mean every sound complaint should be dismissed. Our noise guide covers measurement and siting questions.

Fault codes and repeated resets

Photograph the exact code and note the date, time and circumstances. Use the model-specific owner's manual or official support route, rather than a code list for another manufacturer.

Only carry out a reset if the manual or support professional tells you to. Repeatedly clearing the same fault without investigation can obscure useful information. Keep previous support advice and the result of each action.

If warranty or an installation contract applies, contact the responsible provider promptly. Ask who is investigating, the next step and how you should operate the system while waiting.

A useful fault report

Information	Example of the detail needed
Equipment	Exact outdoor unit, controller and hot-water equipment
Symptom	What fails, where and since when
Conditions	Outdoor weather, room temperatures and occupancy
Settings	User schedule and recent changes
Consumption	Actual readings over identified dates
Evidence	Error photographs, short recordings and commissioning documents
Previous action	What support advised and what happened afterwards

Keep correspondence and agreed visits in writing. If the issue is not resolved, use the contractor's formal complaint process and the relevant warranty or certification route, with the evidence attached.

Troubleshooting FAQs

Should I switch the heat pump off to save money?

Follow the owner's and installer's advice. Switching off can interfere with protection or recovery, and does not identify why consumption is high.

Can I top up pressure myself?

Only follow the exact owner's instructions if they expressly permit it and you understand them. Repeated pressure loss needs professional investigation; do not guess from boiler advice.

Is water under the outdoor unit normal?

Condensate and defrost water can be expected, but the installed drainage should manage it appropriately. Report persistent pooling, freezing hazards or signs of an abnormal leak.

How long should I wait before reporting cold rooms?

Report persistent failure to reach the agreed temperature with the recorded conditions. Do not accept an open-ended instruction to wait without an explanation of the expected recovery and review point.

Related guides for your next step

To understand schedules and temperatures at handover, use our heat pump controls and settings guide.

For planned aftercare and warranty records, compare the checks in our heat pump servicing guide.

Sources and scope

This guide uses the linked technical and manufacturer material to structure safe observation and professional escalation. It does not diagnose a particular fault or instruct homeowners to repair electrical, refrigerant or pressurised components.

Images are AI-generated editorial illustrations.