Before the First Cold Snap: An Electrical Handover Checklist for Heat Pumps

Every autumn, Custodian Electrical is asked to attend heat pumps that have already run for a season and are now being relied upon in earnest. The pattern is remarkably consistent. The hydraulic and refrigeration work is usually meticulous, the commissioning sheets are complete, and the unit performs well in mild weather. The electrical installation, by contrast, has often been treated as the final connection rather than as a designed part of the system. It works, so nobody questions it, until the first sustained cold spell arrives and the compressor, the immersion backup and the controls all draw at once.

Why the electrical side slips through

Heat pump projects are typically led by an MCS-certified heating engineer. The electrical works is subcontracted late in the programme, or added to an existing electrician's visit, and the brief reduces to a single instruction: provide a supply. That framing is where the difficulty begins. A heat pump is not a boiler swap. It has inverter-driven electronics mounted on the outside of a building, a backup heater with a considerable load, low-voltage control wiring that crosses a trade boundary, and a manufacturer's instruction set that frequently specifies protection arrangements beyond the default.

For property managers overseeing a portfolio, the practical question is not whether the heating works today, but whether the electrical evidence exists to demonstrate that it was installed correctly. The checklist below is organised around that test.

1. Confirm the supply is genuinely dedicated

The outdoor unit should be served by its own circuit from the consumer unit, sized against the manufacturer's data for both running and starting current. Where a backup immersion heater is fitted, it should normally have a separate circuit rather than sharing a way with the compressor. Cable sizing must account for voltage drop over what can be a long run to an external wall position, particularly in larger properties where the consumer unit sits at the far end of the building.

The wider supply question deserves an early answer. If a property already carries an electric vehicle charge point, an electric shower and a heat pump, the capacity of the cut-out fuse and the adequacy of the earthing arrangement should be reviewed deliberately rather than discovered by nuisance tripping in December. Where the calculated maximum demand approaches the service capacity, a distribution network operator application may be required. That is a September conversation, not a January emergency.

2. Isolation should be local, lockable and legible

A means of isolation positioned within sight of the outdoor unit allows a service engineer to work safely without walking back through the property to find the consumer unit. The enclosure must be appropriate to the location, with an ingress protection rating suited to an exposed wall, and the device must be clearly identified. Labels applied with a marker pen have a working life measured in months; engraved or printed labels survive a decade of weather and plant-room dust.

3. Agree where the controls end and the electrician's work begins

Room sensors, weather compensation, cylinder thermostats and any signal wiring to a smart tariff controller sit awkwardly between two trades. The most common defects we encounter are sensor cables clipped alongside power cables, terminations left loose in a joint box, and no record of which party tested what. This should be settled in writing before work starts. It is also worth confirming that the controller retains its commissioning parameters after a power interruption, and that those parameters have been recorded somewhere other than the installer's phone.

4. Surge protection is not an optional refinement

An inverter assembly mounted on an external wall is precisely the profile of equipment that transient overvoltage damages. A Type 2 surge protective device at the origin is modest in cost when compared with replacing a control board, and a second device at a detached plant room or outbuilding may be justified where the cable run is long or the exposure is high. The SPD's status indicator should be added to the planned maintenance schedule, because a device that has absorbed a surge is silent about having done so.

5. Earthing, bonding and residual current protection

Three checks are routinely skipped. First, main protective bonding to incoming metallic services: a heat pump conversion often removes a gas supply, and bonding conductors are sometimes left disconnected rather than formally removed and re-recorded. Second, the pipework question: whether heat pump flow and return pipework constitutes an extraneous conductive part depends on whether it introduces earth potential into the installation, which in turn depends on the material and route. This should be verified rather than assumed in either direction. Third, the residual current device: inverter-driven compressors can generate smooth DC residual current, and manufacturer's instructions commonly call for a Type A device and occasionally a Type B. Follow the instructions, and record the reasoning on the certificate so the next person does not have to guess.

6. What should change hands at handover

• The electrical installation certificate or minor works certificate, with a schedule of test results for the heat pump circuit
• Building Regulations notification evidence where the work is notifiable
• The manufacturer's commissioning checklist and warranty registration confirmation
• A one-page electrical schedule: circuit reference, protective device rating, cable type and size, isolator location, SPD type and status, RCD type
• Named contacts for both the electrical contractor and the heating engineer

A simple responsibility map

Task	Usual owner	Evidence
Circuit design and certification	Electrical contractor	Certificate and schedule of test results
DNO notification	Lead installer	Application reference
RCD type in line with instructions	Electrical contractor	Note against the certificate
Controls commissioning	Heating engineer	Commissioning sheet
Handover pack to landlord or manager	Principal contractor	Signed handover record
Annual SPD and labelling check	Maintenance provider	Planned maintenance record

Book the review before the weather turns

A pre-season electrical review is a short visit. It confirms the circuit documentation exists, the isolation and labelling are sound, the protective devices match the manufacturer's requirements, and the surge protection is intact. Conducted in late September or early October, it leaves time to correct anything found before the system is carrying the full heating load. Conducted in the middle of a cold snap, it becomes an interruption to someone's heating. The former is a routine piece of property management; the latter is an emergency, and it is always more expensive.