Heat Pump Making Noise — What's Normal and What's Not
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Post a job — we'll find you an engineer →Do not remove panels from the outdoor unit or attempt internal inspection — refrigerant pipework is under high pressure.
Heat pumps are remarkably quiet machines compared to traditional boilers, but they're not silent. Most owners quickly get used to the gentle hum of the outdoor unit and the soft sounds of heating fluid circulating indoors. Problems arise when the noise changes — becomes louder, higher-pitched, or takes on an unusual character. This can happen due to wear and tear, environmental factors like debris, or occasionally more serious issues with the refrigerant system or compressor. Since heat pumps are relatively new to many UK homes, it's easy to panic at unfamiliar sounds. This guide helps you distinguish between normal operation and genuine faults, so you'll know whether to monitor the situation or call in a Gas Safe and F-Gas certified engineer straightaway.
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Most likely cause & what to check
Normal heat pump noises: a steady low hum from the outdoor fan and compressor (similar to a quiet fridge), a slight increase in noise when it starts up, gurgling or whooshing sounds during defrost cycles, and gentle flow noises from pipework inside.
Louder than usual humming or droning: if the outdoor unit has become significantly louder than when first installed, the compressor may be working harder due to scale build-up in the system, low refrigerant charge, or a failing component. Have an MCS engineer inspect.
Rattling from the outdoor unit: usually caused by loose screws on the casing, a leaf or debris caught in the fan, or vibration from the fan blades. Turn the unit off and check for visible debris around and inside the fan guard. Do not reach inside the unit.
Clicking or banging when starting or stopping: a small amount of expansion and contraction noise from pipework is normal. Loud banging on startup can indicate a refrigerant issue or a failing compressor — call your installer.
High-pitched squealing: often indicates a refrigerant issue or a bearing failing in the fan motor. This needs an F-Gas certified engineer to inspect promptly.
Noise from the indoor unit (if applicable — e.g. Mitsubishi Ecodan hydrobox, Daikin indoor unit): gurgling from the buffer tank or cylinder is normal. Loud vibration from the indoor unit can often be fixed by checking pipework brackets and anti-vibration mounts are secure.
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Frequently asked questions
Is a humming noise from my heat pump normal?
Yes — a steady, low hum from the outdoor unit is completely normal and similar to a quiet refrigerator. If the hum suddenly becomes much louder or deeper than when you first had it installed, that's worth investigating, as it can signal the compressor working harder due to scale build-up or refrigerant issues.
My heat pump is making a rattling noise — is it dangerous?
Rattling is usually harmless and often caused by loose fixings on the casing or a leaf trapped in the fan guard. Switch the unit off, look for visible debris around the fan, and check that the casing screws are tight (without opening any panels). If rattling persists after clearing debris, contact your installer.
Why does my heat pump make noise during defrost cycles?
Defrost cycles cause the system to reverse flow direction, which creates gurgling, whooshing, and temporary hissing sounds — this is completely normal. You'll typically notice it happening in winter mornings or evenings, and the noise should last only a few minutes.
Should I worry about a high-pitched squealing sound?
High-pitched squealing can indicate a refrigerant leak or a failing bearing in the fan motor, so it does need prompt attention from an F-Gas certified engineer. Don't delay on this one — the sooner you get it checked, the better, as it could develop into a more expensive repair.
What should I do if my heat pump bangs loudly when it switches on or off?
A small amount of clicking or gentle banging from pipework expansion is normal, but loud banging on startup can signal a refrigerant problem or compressor issue. Contact your installer or a qualified engineer rather than waiting to see if it gets worse.
Can I fix heat pump noise myself?
You can safely check for loose casing screws and remove visible debris from around the outdoor unit, but never remove panels or reach inside — refrigerant pipework is under high pressure. For anything beyond basic visual checks, always call a qualified engineer.