Guides · Maintenance

How to maintain your air source heat pump at home and when to call an engineer

DIY checks, annual servicing, warning signs and warranty records

Air source heat pump maintenance: what you can safely check and clean at home

There is a short but useful list of tasks any homeowner can do between professional visits. These keep the system ticking over efficiently and help you catch problems early. They do not replace an annual service, but skipping them between visits is a missed opportunity.

Keeping the outdoor unit clear and clean

The outdoor unit draws air across its coil to extract heat, so anything that restricts airflow reduces efficiency directly. Clear leaves, grass cuttings, and any debris from around the unit regularly and after storms. Keep vegetation trimmed back to the clearance distances specified in your manufacturer's manual, as requirements vary by model. Check the exact figures for your unit rather than relying on a generic rule.

During winter, check that snow is not building up around the base or blocking the fan. What you should not do is remove panels, poke around internal components, or attempt to rinse the coil with a hose unless your manual explicitly permits it and instructs you to isolate the power first. If the manual does not mention it, leave it alone.

Filter checks, vents, and thermostat basics

Some air source heat pumps, particularly air-to-air systems, have accessible air filters that the manufacturer expects homeowners to clean or replace at regular intervals. Check your manual for the schedule and follow it. Washable filters should be fully dry before you refit them. For hydronic (air-to-water) systems with indoor units, the same principle applies to any accessible filter housing.

Inside the house, make sure supply and return vents or fan coil units are not blocked by furniture, curtains, or stored items. Check that thermostat batteries are fresh and that the schedule and temperature settings are still correct, particularly after power cuts, which can reset some controllers.

Spotting early warning signs between services

Train yourself to notice changes. Gurgling sounds can indicate trapped air or a circulation issue. A new rattling or vibration from the outdoor unit suggests something mechanical has shifted. Hissing from pipework near the outdoor unit warrants a call to an engineer. If your radiators are noticeably cooler than usual and bleeding them does not help, that is worth investigating before the next scheduled service.

How often your heat pump needs a professional service

Annual professional servicing is the industry standard across the UK. This is not a precautionary guideline. It is a condition written into the warranty terms of most major manufacturers.

Why annual ASHP servicing is the minimum, not optional

Daikin, Vaillant, Mitsubishi Electric, NIBE, and Samsung all require documented annual servicing to preserve warranty eligibility. Vaillant specifically requires the service to be recorded in the Benchmark logbook. NIBE's seven-year extended warranty is conditional on annual servicing with completed Benchmark documentation. Mitsubishi Electric requires the first service within 12 months of commissioning and every 12 months thereafter, and may request documentary evidence before authorising any warranty work.

Beyond warranty compliance, an annual visit allows the engineer to measure performance against the manufacturer's specifications. A gradual drop in the system's Coefficient of Performance does not announce itself, it just shows up on your electricity bills. Catching it early is significantly cheaper than dealing with the compounding effect over several heating seasons. If you are still comparing what the system should cost to run, the air source heat pump cost guide sets out typical West Midlands running costs for a system that is being looked after.

The best time of year to book your service

Late summer or early autumn is the practical answer. Demand for ASHP engineers rises sharply once temperatures drop, and availability tightens precisely when you need the system most. Booking in August or September means you get earlier appointments, no rush, and any faults identified can be resolved before heating season begins. If your system was installed under the Boiler Upgrade Scheme, your installer's paperwork should confirm the warranty terms, but ongoing servicing is typically arranged independently by the homeowner with a qualified engineer, not provided by the installer.

What a qualified engineer checks during a full annual service

A proper service produces measured readings and a written record. If an engineer arrives, looks around, and leaves without documentation or recorded performance data, that does not meet the standard most manufacturers expect. Here is what a full visit should include.

The outdoor unit, fan, coil, and refrigerant circuit

The engineer inspects the casing, brackets, pipework insulation, and cabling for physical damage or corrosion, then cleans the outdoor coil and fan. Critically, they measure refrigerant operating pressures and temperatures and compare those readings against the manufacturer's specifications. Superheat and subcooling values are checked to confirm the refrigerant charge is correct. Where indicated, a leak test is carried out.

All refrigerant work, including pressure testing, leak detection, and any charging or recovery, must be performed by an F-Gas-qualified engineer. This is a legal requirement, not a preference. When you book a service, confirm the engineer holds the appropriate F-Gas certification.

The hydronic circuit, cylinder, and heating controls

For air-to-water systems, the engineer checks system pressure, cleans the magnetic filter and strainers, inspects the expansion vessel, and tests circulation pump operation. If the system uses glycol antifreeze, the concentration is tested and topped up if necessary. Flow and return temperatures are measured and logged, giving a baseline for future comparisons.

The hot water cylinder, immersion controls, and backup heater are also checked. Electrical connections, thermostats, sensors, weather compensation settings, and fault-code history are reviewed. The engineer should test the full heating and hot-water cycle to confirm the system is operating as designed.

Air source heat pump maintenance checklist: what the final record should show

At the end of the visit, the engineer runs the system through a complete operating cycle and records outdoor temperature, flow and return temperatures, pressures, current draw, and any fault codes. This written record is your proof of service. Keep every service report for the full duration of your warranty period. Without it, a manufacturer can legitimately decline a warranty claim on a compressor or refrigerant-circuit fault on the grounds that documented maintenance cannot be evidenced.

Warning signs that mean you need to call an engineer sooner

Some symptoms should not wait for the next scheduled visit. Knowing which ones to take seriously can prevent a minor fault from becoming an expensive repair.

Noises, pressure loss, and unexplained changes in heating output

Gurgling from pipework usually means trapped air or a circulation problem. Banging or sustained vibration from the outdoor unit indicates a mechanical fault that needs diagnosis. A hissing sound near refrigerant pipework is a potential leak and should be treated as urgent. Cold radiators that do not respond to bleeding, combined with a drop in system pressure, point to a leak somewhere in the system.

Before calling an engineer, run through the basics, confirm the thermostat is calling for heat, check the pressure gauge against the range specified in your manual (typically around 1 to 1.5 bar when cold, but check your specific model), and look for visible water around the unit or pipework. If any of those checks reveal a problem, or if everything looks correct but performance is still poor, call an engineer.

Fault codes, repeated lockouts, and icing

A single fault code that clears after one reset may be a one-off event caused by a temporary power fluctuation. Repeated lockouts or a fault code that keeps returning need professional diagnosis. Common causes include low refrigerant pressure, restricted water flow, air in the system, blocked filters, sensor faults, or pump failure, none of which resolve themselves.

Light frost on the outdoor unit during a defrost cycle is completely normal, the system manages this automatically. Heavy icing that persists beyond a defrost cycle, or ice that builds up on parts of the unit that should not be frozen, is a sign of restricted airflow, a drainage problem, a refrigerant issue, or a defrost-control fault. Do not ignore it. Refrigerant leaks and compressor problems left untreated will escalate quickly.

What a heat pump service costs in the UK and what maintenance contracts cover

Costs vary between standalone bookings and service plans, and knowing the realistic figures for both helps with budgeting. Here are the numbers for 2026.

Typical annual ASHP service fees in 2026

A professional annual service costs between £150 and £300, with around £200 being a reasonable planning figure across the UK. Costs vary by region, system complexity, and whether the visit is booked as a one-off or as part of a service plan. Some manufacturers include the first service in the installation price, so it is worth checking the original contract before paying for something you may already have covered.

Typical annual service

£150–£300

Sensible planning figure

Around £200

Common repair costs to budget for

If a fault is identified during or between services, these are the typical repair costs:

Minor electrical fault

£150–£300

Refrigerant top-up or minor leak repair

£200–£500

Fan motor replacement

£200–£500

Circulation pump replacement

£200–£450

Expansion vessel replacement

£150–£300

Control board replacement

£300–£900

Compressor replacement

£1,000–£2,500

Always check your warranty cover before authorising any major repair. Compressor and control board replacements are the scenarios where a valid warranty makes the biggest financial difference.

What a maintenance contract typically includes

A service-only annual contract typically costs £100 to £200 per year and covers the scheduled visit, performance checks, cleaning, and filter inspection. Repairs and parts are usually charged separately. Monthly care plans spread the cost over 12 payments at roughly £10 to £20 per month and often include priority call-out slots. Service-plus-repair contracts cover breakdowns and labour but carry exclusions, age limits, and claim limits that need careful reading before signing. Major component replacements are rarely included unless a premium plan explicitly states otherwise.

How regular servicing protects your warranty and keeps bills down

Warranty conditions and what happens if you skip a service

Most major manufacturer warranties require documented annual servicing. A missed service year gives the manufacturer grounds to reject a claim on compressor or refrigerant-circuit faults, which are precisely the repairs that cost the most. The warranty terms for your specific model take precedence over general guidance, so read them carefully and follow the exact requirements, including the engineer qualification standards and logbook completion.

Keep copies of every service report, invoice, and the completed Benchmark logbook, both paper and digital, to ensure you always have an accessible, complete record. If you have lost paperwork from previous services, contact the engineer who carried out the work; most reputable companies retain copies.

The link between annual heat pump maintenance and running costs

A dirty outdoor coil, a low refrigerant charge, or restricted airflow all reduce the system's COP. Engineers consistently find, based on field measurements and manufacturer testing, that a noticeably fouled coil reduces seasonal efficiency by around 10 to 15%, and severe blockage can push that figure above 20%. The electricity increase is larger than the COP reduction in percentage terms, reducing COP from 3.0 to 2.7 requires roughly 11% more electricity to deliver the same heat output. Over a full heating season in a typical UK home, that is a meaningful addition to your energy bills for what amounts to a preventable problem.

Regular servicing keeps coil condition, refrigerant charge, airflow, and system pressure where the manufacturer designed them to be. That is where the efficiency figures in your original BUS application came from, and it is where they need to stay for the system to deliver on its long-term promise.

Stay on top of air source heat pump maintenance and the system looks after itself

The air source heat pump maintenance picture is simpler than most homeowners expect once it is laid out clearly. Do the straightforward DIY checks regularly, clear the outdoor unit, check accessible filters, confirm vents are unobstructed, and listen for anything unusual. Book a professional annual service in late summer before the heating season starts. Keep every service report. Act on warning signs rather than waiting for the annual visit.

Green Glow installs your system, handles the Boiler Upgrade Scheme application, and registers it with the manufacturer, we don't provide ongoing servicing or maintenance contracts. If your system develops a fault within its manufacturer warranty period, contact the manufacturer directly, they handle warranty repairs, not your installer. For routine annual servicing, use an F-Gas-qualified engineer and keep every report for your records.

If your heat pump is approaching its first anniversary and a service has not been confirmed, now is the right time to act. The annual service fee is modest compared to a compressor replacement or a rejected warranty claim. Keep up with it consistently, and your heat pump should deliver the reliable, efficient heating it was designed for, for a decade or more, according to many manufacturers and industry sources.

Already considering a heat pump, not just maintaining one?

If you're reading this because you're deciding whether to make the switch, the maintenance picture above is the honest full story, not a reason to hesitate. A well-maintained air source heat pump is a reliable, efficient system for a decade or more. Green Glow handles the installation and the Boiler Upgrade Scheme application, with a free home survey and a fixed quote before you commit to anything.