E51 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution HM gen 1: Continuous deviation on power transistor for 15 minutes (also shown as E41)
Short answer
On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, E51 means: Continuous deviation on power transistor for 15 minutes (also shown as E41). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Continuous deviation on power transistor for 15 minutes (also shown as E41).
Part involved: Inverter error.
When it shows: 15 min continuous.
Likely causes:
- Defective fan motor; defective inverter PCB in outdoor unit; defective control PCB in outdoor unit.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: yes (switch SF1 off/on per user manual).
What you can check
- Note the alarm number/text shown on the display. Check the consumer-unit breakers/isolators for the indoor and outdoor units are on. Check the outdoor unit is not blocked by leaves, snow or ice and its drain is clear (look only - do not open the casing). The user manual allows resetting by switching the indoor unit off and on with switch SF1; if the alarm cannot be reset, hold the operating-mode button to select 'Add. heat only' (immersion heating) and contact the installer. Recurring alarms mean an installation fault.
What the engineer will check
- Refrigerant-side and PCB checks per HM-T-193 flowchart: check sensor resistances (Tho-R/A/D/S, LPT), 63H1 switch, service valves, refrigerant charge, fan motor and fuse F2, inverter/control PCBs, supply voltage.
Who to ask for: Heat pump / refrigeration engineer (manufacturer-trained).
Certification: F-gas certification for refrigerant-circuit work; electrical competence (Part P/18th Edition) for PCB/wiring.
What you might notice
Sources
- Technical Manual HM-T-193 - Air to Water Heat Pump (Hydrolution) ↗ · '13 HM-T-193 (updated December 18, 2014) · page ML p.157; flowchart p.182 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026