Heat pumps · Error codes · Mitsubishi Heavy Industries Air-Conditioning Europe

E54Mitsubishi Heavy Industries Air-Conditioning Europe · Hydrolution HM gen 1 (HMA100V/HMS140V integrated-controller systems)

E54 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution HM gen 1: Sensor fault, low pressure sensor in outdoor unit

Short answer

On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, E54 means: Sensor fault, low pressure sensor in outdoor unit. 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: Sensor fault, low pressure sensor in outdoor unit.

Part involved: S. fault LPT.

Likely causes:

Open/short circuit on sensor input; sensor does not work; defective control PCB; fault in the refrigerant circuit.

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

Display backlight flashes and status lamp red; some alarms switch to 'Add. heat only' at minimum supply temperature (low heat / higher electricity use)

Sources

Technical Manual HM-T-193 - Air to Water Heat Pump (Hydrolution) ↗ · '13 HM-T-193 (updated December 18, 2014) · page ML p.158 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026