Heat Pump Annual Servicing: Maintenance Checklist, F-Gas Requirements and COP Monitoring

Quick Answer: A heat pump should be serviced annually to maintain efficiency, comply with most manufacturer warranties, and meet MCS expectations. The water/electrical side can be serviced by a competent heating engineer, but any work on the sealed refrigerant circuit requires an F-Gas certified engineer (City & Guilds 2079 / equivalent) under the GB F-Gas Regulation. Core annual tasks are coil cleaning, condensate-drain checks, glycol/inhibitor testing, system-pressure and filter checks, controls/weather-compensation verification, and recording flow/return temperatures to track COP.

Summary

Heat pumps are often sold as "fit and forget", and mechanically they are far simpler to maintain than a combustion boiler — there is no flue, no combustion analysis and no gas. But "low maintenance" is not "no maintenance". An annual service protects the manufacturer warranty (most require documented annual servicing), keeps the seasonal efficiency (SCOP) where it was designed to be, and catches the slow failures — fouled coils, a weak condensate run, falling glycol concentration, a clogged magnetic filter — before they become a no-heat callback in midwinter.

The single most important boundary for any tradesperson is the refrigerant circuit. The sealed system containing R32, R410A or R290 is governed by the GB F-Gas regime. Breaking into, recovering from, or recharging that circuit is restricted to F-Gas qualified engineers, and for flammable refrigerants like R290 (propane) there are additional safety competencies. A general heating engineer can and should service everything on the water and electrical side, but must not touch the sealed circuit without the qualification.

The third pillar is performance monitoring. Unlike a boiler, a heat pump's running cost is exquisitely sensitive to flow temperature and system condition. Recording flow/return temperatures, electrical input, and (where metered) heat output at each service lets you compute or estimate the running COP and spot a system that has quietly drifted from a SCOP of 3.5 down to 2.5 — doubling the homeowner's bills without ever "breaking".

Key Facts

• Annual service interval — recommended yearly; check the specific manufacturer's warranty terms, as missing a documented service can void cover.
• F-Gas boundary — work on the sealed refrigerant circuit (recovery, leak testing into the circuit, recharge) requires F-Gas certification (e.g. City & Guilds 2079, Cat I) under the GB Fluorinated Greenhouse Gases Regulations.
• Leak-check thresholds — equipment containing 5 tonnes CO₂-equivalent or more of F-gas requires periodic leak checks; most domestic monobloc ASHP are factory-sealed and below this, but split systems with larger charges can be in scope.
• R290 (propane) — increasingly used in new heat pumps; A3 flammable refrigerant requiring additional handling competence and exclusion-zone awareness.
• Coil/evaporator cleaning — outdoor coil fins must be kept clear of leaves, fur, pollen and debris; fouling raises defrost frequency and cuts COP.
• Condensate management — the outdoor unit produces condensate (and meltwater in defrost); the drain must be clear and frost-protected or it ices up and damages the fan/casing.
• Glycol/inhibitor — primary circuits (especially with outdoor pipework) use antifreeze + inhibitor; concentration and pH should be checked annually with a refractometer and test kit.
• Magnetic filter — fit and clean a magnetic system filter; iron-oxide sludge protects neither the heat pump's plate heat exchanger nor the pump.
• System pressure — check sealed-system pressure and expansion-vessel charge; low pressure trips many units to lockout.
• Weather compensation — verify the heating curve is set and working; a defeated/overridden curve is the most common cause of poor efficiency.
• COP/SCOP — Coefficient of Performance = heat out ÷ electricity in; track it across services to detect efficiency drift.
• Electrical — check terminals, RCD/RCBO operation, isolator, and any backup immersion/heater element.

Quick Reference Table

Detailed Guidance

The annual service checklist

Heat-pump annual service
------------------------
OUTDOOR UNIT
[ ] Visual inspection: casing, fan blade, mounting feet/anti-vibration
[ ] Clean coil/fins (soft brush / fin comb / low-pressure rinse — never
    bend fins or jet-wash hard)
[ ] Clear vegetation/debris from intake & discharge; check clearances
[ ] Condensate tray & drain clear; trace heating / drain heater working
[ ] Listen/observe a defrost cycle if conditions allow

WATER SIDE
[ ] System pressure correct; top up & re-pressurise if needed
[ ] Expansion vessel charge checked
[ ] Magnetic filter cleaned; note sludge quantity
[ ] Glycol concentration (refractometer) & inhibitor/pH test
[ ] Circulator pump operation & speed/curve setting
[ ] Check for leaks at unions, valves, cylinder coil

CONTROLS & PERFORMANCE
[ ] Weather-compensation curve set & active (not overridden)
[ ] Flow temperature appropriate (as low as comfort allows)
[ ] DHW cylinder reheat & legionella cycle working
[ ] Buffer/volumiser & low-loss header (if fitted) functioning
[ ] Record flow temp, return temp, ambient, electrical input;
    compute/estimate COP and compare to previous services

ELECTRICAL
[ ] Isolator, RCD/RCBO test, terminal tightness, backup heater
[ ] No fault/error history of concern in the controller log

REFRIGERANT (F-GAS CERTIFIED ENGINEER ONLY)
[ ] Visual leak signs (oil staining); formal leak test where in scope
[ ] Operating pressures/temperatures within spec
[ ] F-Gas logbook updated if circuit worked on

The F-Gas line you must not cross

Refrigerant work in GB is regulated. To recover refrigerant, break into the sealed circuit, leak-test the circuit, or recharge, the engineer needs the relevant F-Gas qualification and the business must be F-Gas registered. For most domestic monobloc heat pumps the refrigerant circuit is hermetically sealed and factory-charged, so routine servicing never opens it — a general engineer can do the whole annual service. The moment a refrigerant fault is suspected (low pressures, poor heating despite a clean system, oil staining), it becomes an F-Gas job. Do not "top up" or vent refrigerant without certification — it is both illegal and unsafe, especially with flammable R290.

Equipment holding 5 tonnes CO₂-equivalent or more of F-gas is subject to mandatory periodic leak checks and record-keeping; the interval depends on the charge size. Smaller domestic charges typically fall below this, but verify the unit's refrigerant type and charge against the threshold rather than assuming.

Monitoring COP and spotting efficiency drift

COP = useful heat output (kW) / electrical input (kW)

Worked estimate:
  Heat meter shows  6.0 kW delivered to the heating circuit
  Clamp meter shows 1.7 kW electrical input
  COP = 6.0 / 1.7 = 3.5   (healthy for the conditions)

If last year at the same ambient/flow temp it was 3.6 and now 2.6:
  -> investigate fouled coil, low glycol, defrost faults,
     a defeated weather curve, or a refrigerant issue.

If a heat/electricity meter is installed, log the readings. If not, recording flow/return/ambient and input each year still reveals trends. A heat pump rarely "stops" — it quietly costs more, so the homeowner's bill is the symptom and the service log is the diagnosis.

Seasonal and weather-related tasks

• Autumn — clear leaves from the coil and confirm the condensate drain and any drain trace-heating work before the first hard frost.
• After heavy snow/ice — check the unit is not buried and the defrost cycle is coping; excessive defrosting points to airflow, sensor or refrigerant issues.
• Glycol — top-up water dilutes antifreeze over time; re-test concentration annually, especially on systems with outdoor pipe runs.

Frequently Asked Questions

Do heat pumps legally need an annual service?

There is no single legal duty to service a domestic heat pump the way gas appliances have safety duties, but most manufacturers require documented annual servicing to keep the warranty valid, and MCS-installed systems come with a maintenance expectation. Practically, the annual service is what preserves both the warranty and the efficiency the customer is paying for, so treat it as essential rather than optional.

Can a normal heating engineer service my heat pump?

Yes for the water and electrical side — pressure, glycol, filter, controls, weather compensation, condensate, electrical checks. No for the sealed refrigerant circuit, which requires an F-Gas certified engineer. For routine annual servicing of a monobloc unit the circuit is never opened, so a competent heating engineer can do the full service; bring in F-Gas competence only if a refrigerant fault is suspected.

What is a good COP, and how do I know mine has dropped?

A well-designed UK air-source heat pump should achieve a seasonal COP (SCOP) of roughly 3–4 — three to four units of heat per unit of electricity. Day-to-day COP varies with outdoor temperature and flow temperature. You detect a drop by recording flow/return temps and electrical input at each service (and reading any heat meter): a fall at comparable conditions points to a fouled coil, low glycol, excessive defrosting, an overridden weather curve, or a refrigerant fault.

Why is the outdoor unit icing up so much?

Some frosting and periodic defrost cycles are normal in cold, damp weather — the unit reverses briefly to melt frost off the coil. Excessive icing means a problem: a blocked condensate drain refreezing, a fouled coil restricting airflow, a failed defrost/frost sensor, or a refrigerant-charge issue. Clear the coil and drain first; if it persists, get a fault diagnosis (and F-Gas competence if refrigerant is implicated).

Is R290 (propane) dangerous to service?

R290 is propane — a highly efficient but flammable (A3) refrigerant now common in new heat pumps. The water and electrical servicing is the same, but any refrigerant work requires F-Gas certification plus competence in handling flammable refrigerants, with ignition-source controls and exclusion zones. Never attempt refrigerant work on an R290 unit without the proper qualifications and equipment.

Regulations & Standards

• Fluorinated Greenhouse Gases Regulations (GB F-Gas regime) — certification, leak checking, recovery and record-keeping for refrigerant work.

• City & Guilds 2079 (F-Gas Category I–IV) — refrigerant-handling qualifications.

• BS EN 378 — refrigerating systems and heat pumps: safety and environmental requirements.

• BS EN 14511 / BS EN 14825 — heat-pump performance rating (COP/SCOP test conditions).

• MCS / MIS 3005 — heat-pump installation and ongoing standards; maintenance expectations.

• HSE guidance on flammable refrigerants (A2L/A3) — handling R32/R290 safely.

• GOV.UK — F-gas: guidance for users, producers and traders — GB F-Gas obligations and leak-check thresholds.

• MCS — heat pump standards — installation and maintenance requirements.

• HSE — refrigerants and F-gas — safety guidance for refrigerant handling.

• BSI — BS EN 378 / BS EN 14511 — refrigeration safety and performance standards.

• f gas regulations heat pumps — the F-Gas rules in full

• heat pump cop scop explained — COP and SCOP defined with worked numbers

• heat pump commissioning checklist — baseline figures to compare services against

• heat pump faults — diagnosing common heat-pump faults

• magnetic filters — system filtration that protects the heat pump