If you own an Air Source Heat Pump in Orpington, Bromley, Sevenoaks or anywhere across South East London and Kent, an annual service isn't optional — it's essential. Yet many homeowners skip it, either because they don't know what's involved or because their original installer never explained the importance.
As a CIPHE member and heat pump engineer working on systems every day, I want to demystify exactly what a proper ASHP service includes, why it matters, and what happens when it's neglected.
Why Annual Heat Pump Servicing Is Non-Negotiable
An Air Source Heat Pump is a sophisticated piece of refrigeration engineering — closer to a sealed industrial unit than a domestic boiler. It runs continuously through the heating season, exposed to weather, debris and temperature extremes. Without annual servicing, three things happen:
- Efficiency drops off — a dirty evaporator coil and blocked filters make the system work harder for the same output, which shows up on the electricity bill. How much depends on the installation and how dirty it has been allowed to get.
- Manufacturer warranties become invalid — Mitsubishi, Vaillant, Daikin and Samsung all require documented annual servicing by a qualified engineer to keep your multi-year warranty in force.
- Small faults become catastrophic ones — a £40 sensor replacement caught early prevents a £2,000 compressor failure later.
Why it matters: most manufacturers require documented annual servicing for the warranty to remain valid, typically over a five to seven year period. A missed service can mean paying for a repair that would otherwise have been covered — check your own warranty terms for what applies.
What's Actually Checked in a Proper ASHP Service
A genuine annual service should take 90 minutes to two hours. If your engineer is in and out in 20 minutes, they haven't done the work. Here's the checklist I work through on every visit:
1. External Unit Inspection & Clean
The outdoor unit — the part you see in your garden — pulls thousands of cubic metres of air through its heat exchanger every day. Leaves, pollen, spider webs, grass clippings and dust accumulate on the fins. I clean these thoroughly using a soft brush and proprietary coil cleaner. I also check fan blade balance, listen for bearing wear, and inspect the outer casing for damage from weather, animals or vandalism.
2. System Performance Verification
Flow and return temperatures are measured under load and compared against what the system should be achieving. Routine maintenance follows the manufacturer's instructions for the exact model and does not normally involve opening the refrigerant circuit; refrigerant diagnosis and repair is separate work with its own scope.
3. Electrical Connection Testing
Heat pumps draw significant current through their compressor and fan motors. I test all electrical terminations — at the unit, at the isolator, and at the consumer unit — for tightness and signs of arcing or burning. Loose connections are a fire risk and a common cause of intermittent fault codes.
4. Hydraulic System Checks
On the indoor side I check the heating circuit pressure, the expansion vessel charge, the inhibitor levels, and water quality. Sludge in the system kills heat pump efficiency faster than almost anything else. I'll also test the strainer/magnetic filter and clean it if needed.
5. Glycol & Antifreeze Concentration
This is one many cheap "services" skip. The glycol mix in your heat pump's external pipework prevents freezing in winter. Over time the concentration weakens through small losses. I test it with a refractometer — if the protection is below -10°C, your pipes could split during a cold Orpington winter, leading to a £3,000+ emergency repair.
6. Controls, Sensors & Calibration
Modern heat pumps rely on flow sensors, return temperature sensors, ambient sensors and pressure switches. A drifting sensor causes the system to underperform without throwing a fault code. I verify each one against actual measurements and recalibrate where the manufacturer permits it.
7. Performance Test
I run the system through a full operating cycle and measure the actual delivered heat versus electricity consumed — your real-world COP. If it's significantly below the manufacturer rating, something needs investigating before next winter.
8. Written Service Report
You receive a written record showing every check completed, all measured values, any recommendations, and the engineer's qualification number. This document is what your warranty provider will ask for if you ever need to claim.
Warning Signs Your Heat Pump Needs Attention Now
Don't wait for the next service if you notice any of these:
- Unusual noises — grinding, knocking or rattling that wasn't there before
- Ice build-up on the outdoor unit that doesn't clear during normal defrost cycles
- Rising electricity bills with no change in heating habits
- Lukewarm radiators when the system says it's running
- Frequent fault codes on the controller
- Water dripping from anywhere it shouldn't be
How Often, and What Should It Cost?
Once a year, ideally in autumn before the heavy heating season starts. Pricing varies depending on manufacturer, location and access, but a thorough service from a qualified engineer typically falls within a sensible range — and is dramatically cheaper than the repair you'll need without one. Be wary of suspiciously cheap services that don't include proper refrigerant checks or written documentation.
Need a Local Plumber or Heat Pump Engineer?
CIPHE member, covering Orpington, Bromley, Sevenoaks and Kent. Free quotes, no call-out fee, and honest advice.
Need a hand with this?
Smith EcoFlow covers Orpington, Bromley and South East London. A father-and-son firm — no call centre, no subcontractors.
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