A heat pump isn't a boiler. It doesn't fail loudly — it gets tired quietly, and you pay for the tiredness in your electricity bill. The good news: almost nothing breaks in the first decade if you keep up with a small amount of routine housekeeping.
This is the routine our installers run on their own homes. It's split into what you can (and should) do yourself, and what you should leave to an engineer. We've tried to keep it practical — no part of it requires opening a panel or touching refrigerant.
Why it matters
Heat pump efficiency is measured in SCOP (Seasonal Coefficient of Performance) — how many units of heat you get per unit of electricity, averaged over a year. A well-sited, well-maintained unit runs at around 3.5–4.2. A neglected one drifts down to 2.5–3.0. That difference, on a 10,000 kWh heat demand, is roughly £450 a year at 2026 tariffs.
Nothing in this checklist is technically hard. The reason efficiency drops is usually small and dumb — a fence built too close, a filter nobody ever cleaned, a flow rate quietly drifting out of spec. Catch those early and the unit will happily outlive its warranty.
“Ninety percent of the call-outs I do in year five aren't faults. They're dust, leaves, and a homeowner who was never shown where the filter is.”
The seasonal routine
Two ten-minute passes a year. Do one in late spring (after pollen season, before the cooling months if you have a reversible unit) and one in early autumn (before the unit takes up the heating load again).
- Spring pass: outdoor unit clean, indoor filter, drain tray check, cable tie and fin inspection.
- Autumn pass: same again, plus check radiator flow temperature and tenants/occupants know where the thermostat override is.
Outdoor unit — four things
The outdoor unit is where almost all real-world efficiency is won or lost. It needs air to move through it cleanly; anything that interrupts airflow shortens its life and costs you money.
1. Clearance
Check nothing new has grown or been built within 300mm of any face. A hedge planted next to a heat pump in March is a performance problem by September. If you're tight on space, prioritise clearance in front of the fan (the air outlet) — airflow there matters more than behind.
2. Coil & fins
Look at the coil through the grille. If it's matted with seeds, pollen, or cobwebs, rinse with a garden hose on a low setting. Do not use a pressure washer — it'll bend the aluminium fins, and bent fins are permanent. If fins are already bent (a football, a strimmer), a fin comb from any refrigeration supplier will straighten them.
3. Base and drainage
A heat pump produces several litres of condensate a day in winter. Most units drain to a gravel base or a discharge pipe. Check the drainage isn't blocked with leaves or moss, and that water isn't pooling around the unit. Standing water under a unit leads to ice bridging in a cold snap.
4. Cabling and isolator
The isolator switch next to the outdoor unit should be dry, intact, and labelled. A quick visual: no discolouration, no ants (they love warm electrical boxes), no loose cable grommets. If anything looks off, call your installer — don't open the isolator.
Indoor unit & filter
The "indoor unit" is the hydronic box — usually in a utility cupboard or garage — that circulates water to your radiators or underfloor heating. It's mostly sealed and self-managing, with two exceptions.
Strainer filter: there's a Y-strainer on the return pipe that catches any debris in the heating circuit. For the first year after install, check it every six months — you'll likely find some pipe-jointing flash. After that, annually is fine. Isolate, drain, remove the filter, rinse, reseat. Five minutes. Your installer will show you this in the handover; if they didn't, ask.
Pressure gauge: normal reading is around 1.2–1.5 bar cold. If it's drifted below 1.0 or above 2.0, that's the earliest sign something's wrong. Below 1.0 usually means a slow leak somewhere in the radiators. Above 2.0 usually means the expansion vessel is losing its pre-charge. Neither is urgent, but both want a call to your installer within a week.
Refrigerant — hands off
One rule: never touch the refrigerant circuit. Only F-Gas certified engineers can legally work on it, and there's no user-serviceable reason to. If the system is low on refrigerant, you'll see it in performance drop and frost patterns on the outdoor unit — both signs to call in an engineer, not to DIY.
Most modern units also run on R290 (propane), which is efficient and low-GWP but also flammable. This is the other reason for the 300mm clearance rule: it keeps the unit well-ventilated and accessible.
The annual professional service
Once a year, book in a professional service. Most installers offer a fixed-price check-up for around £120–£180, and a few include it free for the first two or three years as part of the install warranty. What a good service covers:
- A full efficiency read (comparing actual SCOP against design SCOP)
- Flow rate and delta-T check across the indoor circuit
- Refrigerant pressure check (F-Gas engineer only)
- Software/firmware update if the manufacturer has pushed one
- Anti-freeze concentration test if you've got a glycol-mix system
- Weather compensation curve tune — this alone is worth the service fee
Red flags to watch for
Call your installer (not emergency, but the same week) if you see any of these:
- A sudden jump in electricity use with no change in weather or occupancy
- The outdoor unit running constantly when the house is already at temperature
- Ice on the outdoor unit that doesn't clear within a defrost cycle
- Water leaking anywhere from the indoor unit (not the expected condensate drain)
- A new, persistent hum, rattle, or grinding noise — heat pumps should be boring
- Pressure gauge drifting by more than 0.3 bar month to month
None of these are emergencies on their own. All of them mean "don't wait six months to mention it at the service."
Save the checklist
A distilled version of the above — short enough to pin inside a cupboard door, or to keep in your pocket. We made it takeable-with-you so you don't need to print anything.
Checklist, on your phone. No paper.
Scan, copy, or email the list to yourself. Tick each item as you go — nothing gets printed, nothing ends up in a drawer.
Decarbr — Checklist, on your phone. No paper. Every six months — 10 minutes [ ] 300mm clearance on all faces of the outdoor unit [ ] Rinse coil with garden hose if it looks matted (low pressure only) [ ] Drainage clear, no standing water around the base [ ] Indoor strainer filter — drain, rinse, reseat [ ] Pressure gauge between 1.2 and 1.5 bar cold [ ] Visual check of isolator box — dry, intact, labelled Every year — engineer visit [ ] Efficiency read against design SCOP [ ] Refrigerant pressure check (F-Gas) [ ] Firmware update if available [ ] Weather compensation curve tuned to this season [ ] Anti-freeze concentration if applicable
Every six months — 10 minutes
- 300mm clearance on all faces of the outdoor unit
- Rinse coil with garden hose if it looks matted (low pressure only)
- Drainage clear, no standing water around the base
- Indoor strainer filter — drain, rinse, reseat
- Pressure gauge between 1.2 and 1.5 bar cold
- Visual check of isolator box — dry, intact, labelled
Every year — engineer visit
- Efficiency read against design SCOP
- Refrigerant pressure check (F-Gas)
- Firmware update if available
- Weather compensation curve tuned to this season
- Anti-freeze concentration if applicable
A note from the author. This piece is drawn from Decarbr's installer network service logs across the 2024–2026 heating seasons. Specifics (pressures, clearances, SCOP ranges) apply to typical air-source units in UK homes — always follow your manufacturer's handbook where it differs.