Air source heat pumps are reliable systems, but like any piece of mechanical and electrical plant, they develop faults. A drop in heating performance, a fault code on the controller, unusual noise from the outdoor unit, or a sudden rise in electricity use are the most common reasons homeowners and property managers call us.
Fix & Repair Engineers provides air source heat pump repair, fault diagnosis, and annual servicing across London and the Home Counties. We work on all major ASHP brands, and our lead engineer is Mitsubishi trained and approved, giving added depth on Ecodan systems specifically. If your existing system needs sorting, servicing, or bringing back up to manufacturer standard, that is our focus.
What Our Air Source Heat Pump Repair & Servicing Covers
Every ASHP callout starts with proper diagnosis rather than guesswork. Depending on what your system needs, our engineers carry out:
Fault Diagnosis
Investigating no-heat, no-hot-water, error codes, and performance complaints using the manufacturer's diagnostic controls.
Refrigerant Circuit Repairs
Leak detection and repair on the refrigerant circuit, carried out under F-Gas regulations by a certified engineer.
Electrical & Control Faults
Diagnosing and repairing faults with sensors, controllers, pumps, valves, and wiring connections.
Annual Servicing
Manufacturer-aligned servicing to protect warranty cover, efficiency, and system lifespan.
Outdoor Unit Faults
Investigating icing, fan faults, defrost cycle problems, and airflow restrictions around the outdoor unit.
Maintenance Contracts
Scheduled servicing for landlords, facilities managers, and commercial operators with multiple systems.
Manufacturer-Trained Expertise
Our lead engineer, Adam, is Mitsubishi trained and approved for air source heat pump work, covering the Ecodan range in particular depth - correct commissioning settings, manufacturer-specific fault codes, and the diagnostic sequences Mitsubishi's own service documentation calls for.
This sits alongside broader experience across other leading brands. Whatever ASHP system you have, we approach it with the same standard: proper diagnosis before any repair, and work carried out to the manufacturer's own service requirements.
Mitsubishi Trained & Approved
Adam holds Mitsubishi's official training and approval for air source heat pump work, alongside current F-Gas certification for refrigerant-circuit repairs. Together, these mean your system is diagnosed and repaired to manufacturer standard, whatever the brand.
Common Air Source Heat Pump Faults We Fix
Most call-outs fall into a handful of recognisable patterns. If you're seeing any of the following, it's worth getting the system looked at before a minor issue becomes a bigger repair:
No Heat or No Hot Water
Often linked to low refrigerant charge, a failed compressor, or a controller fault preventing the system from calling for heat correctly.
Unusual Noise
Grinding, buzzing, or rattling from the outdoor unit can point to fan bearing wear, loose casing panels, or compressor strain.
Icing or Freeze Faults
Excessive icing on the outdoor unit or freeze-protection error codes usually indicate a defrost cycle or airflow problem.
Low Water Flow
Air in the system, a failing pump, or a closed zone valve can trigger low-flow protection and shut the system down.
Rising Electricity Bills
A heat pump working harder than it should to reach the same temperature is a common sign of reduced refrigerant charge or a dirty outdoor coil.
Communication & Control Errors
Loose wiring or a damaged connector between the indoor and outdoor units can produce intermittent faults that are easy to misdiagnose.
Fault & Error Code Reference
Error codes vary between manufacturers, but several patterns come up regularly across the brands we work on, including Mitsubishi Ecodan systems. This table is for reference only - it does not replace a proper diagnostic visit.
| Fault Code / Signal | What It Indicates | Typical Causes |
|---|---|---|
| L3 | Circulation water temperature overheat protection | Low water flow, blocked strainer, or a circulation pump fault |
| L6 | Circulation water freeze protection | Low flow rate, air trapped in the system, or cold-weather shutdown |
| L9 | Low water flow rate on the primary circuit | Air in the circuit, a zone valve or pump not energising, or restricted pipework |
| F3 | Low pressure switch failure | Refrigerant undercharge, a blocked filter, or an expansion valve fault |
| F5 | High pressure switch failure | A blocked outdoor coil, fan fault, or refrigerant overcharge |
| E6 / U1 | Indoor/outdoor communication error | Loose or damaged wiring connections, or electrical interference |
Annual Servicing and Warranty Compliance
Most manufacturer warranties on air source heat pumps run for seven to ten years, and the large majority require documented annual servicing to remain valid. A missed service is one of the most common reasons a warranty claim gets refused.
What's Included in a Service Visit
- Clearing debris and checking clearance around the outdoor unit
- Filter and strainer inspection and cleaning
- Visual refrigerant circuit and leak check (F-Gas engineer)
- Electrical connection and control panel inspection
- Defrost cycle and control settings check
- Water pressure and flow rate check on the primary circuit
Why It Matters
- Protects manufacturer warranty cover on the system
- A poorly maintained heat pump can use noticeably more electricity to deliver the same heat output
- Small refrigerant or flow issues caught early avoid larger compressor or pipework repairs
- Gives landlords and facilities managers a documented maintenance record
Our Repair & Service Process
We keep the process straightforward, whether it's a straightforward annual service or a fault that needs proper investigation.
Tell Us What's Happening
Call or fill in our enquiry form with the brand and model if known, any error code shown, and a description of the fault.
Diagnostic Visit
Our F-Gas certified, manufacturer-trained engineer inspects the indoor and outdoor units and reviews the controller's fault history.
Clear, Itemised Quote
We explain what's wrong and provide a transparent quote before any repair work goes ahead.
Repair or Service Carried Out
Work is completed to manufacturer specification. Any refrigerant-circuit work is handled under F-Gas regulations.
Testing & Documentation
We test the system before leaving and provide service or repair documentation for your records.
Areas We Cover
We provide air source heat pump repair and servicing across London and the Home Counties, including: