Mitsubishi Ecodan Heat Pump Error Codes: Complete Diagnostic Guide

Summary

Mitsubishi Electric's Ecodan range is one of the most widely installed air source heat pumps on UK Boiler Upgrade Scheme (BUS) projects, available in Standard (R410A legacy and R32 current), Zubadan (low-ambient, cold-climate optimised), and Hydrodan configurations. Ecodan systems are controlled through the FTC (Flow Temperature Controller) hydraulic unit and displayed via the wired PAR controller or the wireless MELCloud app, both of which show fault codes when the system locks out.

Mitsubishi Electric uses a broadly consistent fault code letter-prefix system across its residential and light-commercial ranges — the same general categories (P for protection/sensor, E for communication, F for refrigerant-side protection, U for compressor/power) appear whether you're working on a Mr Slim split, a City Multi VRF system, or an Ecodan. However, unlike Daikin's near-identical numbering across its range, Mitsubishi's exact numeric codes and their precise meaning do shift more between product families and generations, so this guide presents the general fault categories with the specific codes best-documented for Ecodan, while flagging where the exact number should be confirmed against the FTC service menu or installation manual for the model fitted.

As with all UK heat pumps, refrigerant-circuit diagnosis and any work on the sealed system — pressure testing, leak detection, recovery, or recharge — requires F-Gas certification under the Fluorinated Greenhouse Gas Regulations. A significant proportion of Ecodan call-outs, particularly drain and sensor faults, are outside the refrigerant circuit and can be diagnosed by any competent heating engineer.

Key Facts

• Controller — fault codes display on the wired PAR remote controller and/or the FTC hydraulic unit's own interface; also visible remotely via the MELCloud app where fitted
• FTC (Flow Temperature Controller) — the hydraulic control unit that manages flow temperature, weather compensation, DHW priority, and displays system status/fault codes; distinct from the outdoor refrigerant unit
• Fault code check function — the PAR controller has a dedicated "check" menu that displays the current or most recent error code and unit number, useful for confirming which part of a multi-unit system has faulted
• P-series codes — generally sensor, drainage, and protection-related faults (e.g. room thermistor, pipe thermistor, drain pump/float switch)
• E-series codes — generally communication faults between the remote controller, FTC, and outdoor unit
• F-series codes — generally refrigerant-circuit protection faults on the outdoor unit (discharge temperature, pressure)
• U-series codes — generally compressor and inverter-related faults, including overcurrent protection
• Legionella cycle — Ecodan cylinders run a periodic anti-legionella heat-up (typically to 60°C); a fault or interruption during this cycle can trigger a DHW-related alarm distinct from a heating-circuit fault
• Booster heater / immersion faults — the backup electric heater has its own fault indications distinct from the heat pump's refrigerant-side codes; check this separately if DHW recovery is slow but the heat pump itself shows no fault
• F-Gas Regulations — recovery, leak testing, and recharge of the refrigerant circuit require F-Gas certification; drain, water-side, and controller/communication faults do not
• MCS commissioning record — Ecodan installations under MCS should have commissioning data (design flow temp, weather compensation curve, heat loss calculation) recorded — a useful reference when a "fault" is actually a design/commissioning issue rather than a component failure
• Exact codes are generation-specific — Standard Ecodan (R410A), Ecodan R32, and Zubadan models do not share an identical fault code table; always confirm the exact code against the FTC/PAR service manual for the specific unit before ordering parts

Quick Reference Table

Confirm the exact code and its meaning against the FTC service code list for the specific Ecodan generation — Standard R410A, Ecodan R32, and Zubadan units differ in their precise numbering.

Detailed Guidance

Fault-Finding Decision Tree

START: Ecodan showing a fault code on PAR controller / FTC display
│
├─ STEP 1: Note the exact code and unit number shown on the
│   PAR controller's "check" menu (multi-unit systems can show
│   which specific unit has faulted)
│
├─ STEP 2: Which general category (letter prefix)?
│   ├─ P-series → go to SENSOR/DRAIN branch
│   ├─ E-series → go to COMMUNICATION branch
│   ├─ F-series → go to REFRIGERANT PROTECTION branch
│   └─ U-series → go to COMPRESSOR branch
│
├─ SENSOR/DRAIN BRANCH (P-series)
│   ├─ Drain-related code → check condensate drain for blockage,
│   │   check float switch/drain pump operation, check for
│   │   frozen drain in cold weather
│   ├─ Thermistor code → check connector for corrosion/looseness,
│   │   check resistance against manufacturer's chart if
│   │   accessible, replace sensor if confirmed faulty
│   └─ Freeze/overheat protection → check water flow rate,
│       system pressure, air in system, blocked strainer
│
├─ COMMUNICATION BRANCH (E-series)
│   ├─ Check cable between PAR controller and FTC
│   ├─ Check cable between FTC and outdoor unit
│   ├─ Check for loose terminals, damaged insulation, or
│   │   routing near high-current cables (EMI)
│   └─ Power-cycle FTC and outdoor unit isolator, confirm
│       whether fault clears and recurs
│
├─ REFRIGERANT PROTECTION BRANCH (F-series)
│   ├─ STOP — check non-refrigerant causes first:
│   ├─ Outdoor unit airflow — coil clean, clearances adequate
│   ├─ Is unit mid-defrost? (normal in cold, humid conditions)
│   ├─ Outdoor isolator and supply voltage within tolerance
│   └─ All normal, code persists → F-Gas certified engineer to
│       check refrigerant pressures and charge
│
└─ COMPRESSOR BRANCH (U-series)
    ├─ Check outdoor unit power supply and isolator
    ├─ Check outdoor unit airflow and coil condition
    ├─ Do NOT repeatedly reset — repeated resets on a genuine
    │   compressor overcurrent trip risk further damage
    └─ F-Gas certified engineer required to check compressor
        electrical characteristics and refrigerant charge

Drain and Water-Side Faults (P-series)

A disproportionate number of real-world Ecodan "faults" are water-side or condensate-related rather than refrigerant faults, and none of these require F-Gas certification:

• Condensate drain blockage or freeze — the outdoor unit's defrost cycle produces meltwater that must drain away; a blocked or frozen drain in cold weather causes water to back up and can trigger a protection code. Check the drain route for blockage, correct fall, and (in exposed locations) whether a trace-heated or insulated drain is needed.
• Float switch/drain pump faults — where a drain pump is fitted (common on internal hydro-box units without gravity drainage), a failed float switch or pump will trigger a specific drain-fault code. Test the float switch mechanically and check pump operation directly.
• Low water flow / freeze protection — a restricted flow rate (closed valve, air lock, blocked strainer, failed circulating pump) can trigger freeze or overheat protection on the water side. Check strainer cleanliness, pump operation, and system pressure before suspecting the heat pump itself.

Communication Faults (E-series)

Communication faults between the PAR remote controller, the FTC hydraulic unit, and the outdoor refrigerant unit are common and rarely indicate a failed component:

• Check all control cable terminals for tightness and corrosion, particularly at the FTC and outdoor unit connection points
• Inspect cable routing for physical damage or proximity to unscreened power cables that could cause interference
• Confirm the outdoor unit's power supply is stable — brief supply dips during compressor start-up can occasionally trigger transient communication faults on marginal installations
• Power-cycle following the manufacturer's procedure (typically isolating the FTC and outdoor unit, waiting several minutes, then restoring power) and monitor whether the fault recurs

Refrigerant Protection and Compressor Faults (F/U-series)

F and U-series codes point towards the refrigerant circuit or compressor, but — exactly as with other manufacturers — the majority of real callouts trace back to conditions outside the sealed circuit:

1. Outdoor unit airflow — check the coil is free of leaves, dust, and debris, and that installation clearances meet the manual's requirements. Restricted airflow is a very common and easily fixed cause of pressure-related protection trips.
2. Defrost cycle — confirm whether the unit is mid-defrost (fan stopped, some icing visible, compressor running briefly) before assuming a fault; this is normal Ecodan behaviour in UK winter conditions.
3. Electrical supply — check the outdoor unit's dedicated isolator and confirm supply voltage is within the rated tolerance; undervoltage under compressor start-up load is a genuine cause of protection trips, particularly on long or marginally-sized supply runs.
4. Water-side restriction — as with sensor faults, a restricted flow rate on the water side can cause the refrigerant-to-water heat exchanger to overheat on the refrigerant side, producing a code that looks like a refrigerant fault but is actually a hydraulic restriction.

Only once airflow, defrost status, electrical supply, and water flow have all been confirmed normal should refrigerant charge and compressor electrical testing (both F-Gas certified activities) be considered.

Booster Heater and DHW-Related Faults

Ecodan cylinders typically include a backup immersion/booster heater for DHW top-up and the periodic anti-legionella cycle (commonly a heat-up to 60°C on a set schedule). A fault during this cycle, or a booster heater fault, presents differently from a heating-circuit fault and is worth checking separately if the symptom is specifically slow or absent hot water recovery with the heating circuit otherwise unaffected — check the booster heater's own thermal cutout/overload and its wiring before assuming a heat pump refrigerant fault.

Frequently Asked Questions

Where do I find the exact fault code meaning for my specific Ecodan model?

The PAR controller's check menu shows the code and unit number; cross-reference this against the service manual for the specific FTC and outdoor unit model combination (Standard, R32, or Zubadan) fitted, since the precise numeric code table differs by generation. Mitsubishi Electric's installer portal and product documentation hold model-specific service code lists — always verify against the correct model before ordering replacement parts.

Can I reset an Ecodan fault code myself?

For sensor, drain, and communication faults, a single reset (power-cycle per the manufacturer's procedure) while also addressing the likely physical cause (blocked drain, loose connector) is reasonable. For compressor and refrigerant-pressure related codes, do not repeatedly reset — if the fault recurs immediately after a reset, further resets risk compressor damage, and diagnosis should move to an F-Gas certified engineer if refrigerant involvement is suspected.

The Ecodan shows no fault code but heating performance is poor — what should I check?

Absence of a fault code means the unit believes it's operating within normal parameters, so investigate settings and design first: flow temperature setpoint and weather compensation curve on the FTC, DHW priority settings (heating can be paused during DHW heat-up on some configurations), and actual flow rate/ΔT across the unit. See the general heat pump fault-finding guide for the broader low-COP diagnostic approach that applies across all manufacturers.

Does MELCloud show fault codes, and is it useful for remote diagnosis?

Yes — where the property has MELCloud connectivity, the app shows current status and can display fault history remotely, which is useful for a first-pass diagnosis or triage call before an on-site visit, particularly for intermittent faults that may have cleared by the time an engineer arrives. It does not replace on-site diagnosis for anything beyond straightforward settings or communication issues.

Regulations & Standards

• Fluorinated Greenhouse Gas Regulations (retained UK law from EU Regulation 517/2014) — F-Gas certification required for any refrigerant-circuit work

• MIS 3005-D / MIS 3005-I — Microgeneration Certification Scheme Heat Pump Design and Installation standards (split from the single MIS 3005 into separate Design and Installation standards from 1 April 2022); current issue 1.0 (2025) — confirm the specific edition against the MCS Standards & Tools Library before relying on detail

• BS EN 14511 — Air-to-water heat pumps; rating conditions and test methods

• Boiler Upgrade Scheme (BUS) — Ofgem-administered grant scheme; ongoing maintenance by an appropriately qualified engineer required to preserve grant compliance

• Part L of the Building Regulations — energy efficiency requirements relevant to heat pump installation and major component replacement

• BS 7671 (IET Wiring Regulations) — applicable to electrical fault-finding on the outdoor unit isolator, booster heater, and control cabling

• Mitsubishi Electric UK — Ecodan Product and Service Documentation — installation, maintenance, and fault code reference by model

• GOV.UK — F-Gas Regulations Guidance — certification requirements for refrigerant work

• MCS — Heat Pump Installation Standards — MIS 3005 Design/Installation standards and commissioning requirements

• Ofgem — Boiler Upgrade Scheme — grant maintenance conditions

• heat pump faults — general ASHP fault-finding: low COP, defrost cycles, common cross-manufacturer causes

• heat pump defrost — normal vs excessive defrost cycle diagnosis

• heat pump cylinders — cylinder coil sizing, buffer tanks, and legionella cycle requirements

• heat pump servicing — annual servicing requirements and F-Gas leak-check thresholds