Seasonal heat pump maintenance

Safe owner checks and competent servicing for air, ground and water-source heat-pump systems.

Heat-pump maintenance protects heat transfer, water flow, freeze protection, controls and safety devices. It is not limited to cleaning an outdoor coil, and it is not a reason for an owner to open refrigerant, electrical or pressurised parts.

Follow the installed product’s instructions and warranty terms. A generic checklist is useful only where it does not contradict the manufacturer or the system design.

Service interval and records

The manufacturer and warranty define the required service interval and competent-person conditions. As at 22 July 2026, the Heat Pump Association’s air-to-water service checklist says systems should be serviced annually in line with manufacturer recommendations, with the work entered in a service record. It also says its checklist is a fallback reference, not a replacement for product-specific instructions.

Keep invoices and completed records with the original commissioning documents. Record model and serial numbers, date, engineer, measured results, faults found, remedial work and any settings changed.

Service cost depends on system type, location, access and scope.

Safe owner checks

An owner can usually make visual checks without tools or removing covers. The product manual takes priority.

Outdoor air-source unit

Keep the specified air inlet, outlet and service clearances free of leaves, vegetation, snow and stored items.
Look for physical damage, persistent ice, oil staining, loose panels or a fan striking its guard.
Check that defrost water drains safely and is not creating hazardous ice.
Listen for a new mechanical rattle or grinding sound.
Do not pressure-wash the coil, bend fins, chip ice from it or pour hot water over it.

Heating circuit

Check the normal pressure indication if the handover instructions ask for it.
Look for water leaks, damaged external insulation and corrosion around valves or joints.
Note rooms that have become slow to warm or emitters that remain cold.
Keep the electrical supply on where it powers frost-protection pumps or trace heating.

Controls and records

Review active alarms and fault history.
Check controller date, time, schedules and internet connection where needed.
Compare energy use and heat delivery with similar conditions, not simply the previous day.
Confirm that a scheduled hot-water hygiene process completes where one forms part of the system design.

A falling pressure, repeated reset or recurring alarm needs diagnosis. Continually topping up the circuit adds fresh oxygenated water and can hide a leak or expansion-vessel fault.

What a competent service covers

The exact procedure depends on the product. An air-to-water service commonly includes:

unit condition, clearances, fan and coil
condensate and defrost drainage
pipe insulation and flexible connections
electrical cables, protective devices and terminals as authorised
signs of refrigerant or oil leakage
water pressure, expansion vessel and pressure-relief path
air vents, strainers, magnetic filters and water quality
primary flow rate and temperature difference
antifreeze concentration or alternative frost-protection devices
pumps, diverter valves, zone valves and bypasses
controller clock, sensors, logs and firmware guidance
domestic hot-water cylinder and associated safety checks
pasteurisation control where required
a complete functional test

Measurements should be compared with the commissioning values and manufacturer limits. “Working when arrived” is not a useful service result on its own.

Only a suitably competent and legally authorised person should work on refrigerant circuits or inside electrical equipment. A monobloc keeps the site water connections outside the refrigerant circuit, but it still contains a sealed refrigerant system.

Water flow and strainers

Reduced flow can lower output, cause noise, interrupt defrost and trigger faults. Strainers and magnetic filters collect debris but create a restriction if neglected.

Cleaning them may involve isolating pressurised hot water, restoring pressure and venting air. It is not automatically an owner task. The service record should state what was cleaned, the debris found and the final pressure and flow.

Persistent sludge or corrosion needs a water-quality investigation. Repeated filter cleaning without addressing the cause is not a complete repair.

Frost protection

Monobloc systems have water outside the heated envelope. Their freeze-protection design may rely on circulation, antifreeze, freeze valves, trace heating or a combination.

At service, verify the method that was designed, the electrical supplies it needs and the condition or concentration required. Do not add antifreeze by guesswork. It affects heat capacity, viscosity, pump duty and materials compatibility.

After a long power cut, low-pressure event or accidental isolation in freezing weather, inspect the system before assuming automatic protection worked.

Domestic hot water

Maintenance should distinguish ordinary cylinder reheating from bacterial-growth control. Check the cylinder sensor, diverter operation, immersion, safety controls and mixing valves as applicable.

A log showing that a pasteurisation programme started does not prove it achieved its required temperature and hold condition. Repeated failure needs investigation, not permanent disabling.

Unvented cylinders and their safety devices require appropriately qualified servicing. Discharge pipework must remain unobstructed and correctly terminated.

Ground and water-source systems

Ground and water-source heat pumps do not have an outdoor fan coil, but they still require source-side checks. Depending on the design, service can include:

brine pressure, flow and antifreeze condition
source pumps, strainers and expansion vessels
manifold, borehole or ground-loop records
abstraction and discharge equipment for open-loop systems
filters, fouling and water-quality effects
permits or consent conditions where applicable

An open-loop water system has different maintenance and legal considerations from a sealed ground loop. Use the design documents and product instructions rather than an air-source checklist.

Before the heating season

Before prolonged cold weather, confirm that airflow or source-side access is clear, pressure is normal, schedules are correct and frost-protection supplies remain energised. Arrange remedial work early if alarms, leaks or drainage problems appeared over summer.

A system used for cooling can collect condensate in additional locations. Check the cooling-mode drainage and insulation specified by the designer before switching back to heating.

Use monitoring as an early warning

A gradual performance change can reveal restricted flow, a high weather curve, unintended immersion use or a sensor fault. Useful records include:

electricity by compressor and supplementary heat where available
delivered heat over the same system boundary
outdoor temperature
flow and return temperatures
run hours, starts and faults
hot-water and space-heating operation

Normalise the comparison for weather and service. Higher winter electricity is expected when the building needs more heat. Investigate a change in relationship, such as higher flow temperature or more backup use in similar conditions.

After maintenance

The engineer should leave the system operating safely, explain defects and update the service and settings records. Confirm that isolating valves, covers and control modes have been restored.

If firmware or parameters changed, retain the old and new versions and the reason. Maintenance should not silently replace a commissioned weather curve or enable supplementary heat.