Guide · Troubleshooting
Heat pump not heating the house enough
Six causes, in the order they are worth checking.
A heat pump that will not bring a UK home up to temperature is most often suffering from undersized radiators, a flow temperature set too low for the emitters installed, or controls scheduling the system off and on like a boiler. Genuine equipment faults are a minority of underheating cases.
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Check in this order
- Is the system running continuously, or being switched off overnight? Continuous low-temperature operation is how heat pumps are designed to work.
- What is the actual flow temperature? If it is 35°C but the radiators were sized for 45°C, rooms will not reach setpoint on cold days.
- Are all radiators heating evenly, or are some cold at the bottom? That points to sludge or air, not the heat pump.
- Are thermostatic valves throttling flow so far that the system short-cycles?
- Is weather compensation active and set to a sensible curve?
- Is the outdoor unit obstructed, iced or recirculating its own cold air?
The design problem behind most cases
If the original heat loss calculation was optimistic, or emitters were left unchanged to keep the quote low, the system simply cannot deliver enough heat at the design flow temperature. Raising the flow temperature will fix comfort and raise bills — the proper fix is upsizing the worst rooms’ radiators.
What to ask your installer
- Provide the room-by-room heat loss figures and compare them to the fitted radiator outputs at the design flow temperature.
- Ask for the commissioning record and the weather compensation curve settings.
- Request a rebalance of the system flow rates.
Frequently asked questions
- Why is my heat pump not heating my house?
- Most commonly undersized radiators for the design flow temperature, boiler-style on/off scheduling, or controls set without weather compensation.
- Should I turn my heat pump up?
- Raising flow temperature restores comfort but costs more. Fixing emitter sizing keeps both comfort and efficiency.
- Is it normal for radiators to feel lukewarm?
- Yes. Heat pump radiators run cooler than boiler radiators and heat the room over a longer period.
- Energy Saving Trust — Heat pump efficiency, running cost and SCOP benchmarks (UK).
- MCS Certified — Installer certification scheme required for grant eligibility.
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