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

E53Mitsubishi Heavy Industries Air-Conditioning Europe · Hydrolution HM gen 1 (HMA100V/HMS140V integrated-controller systems)

E53 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution HM gen 1: Sensor fault, suction gas in outdoor unit (Tho-S)

Short answer

On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, E53 means: Sensor fault, suction gas in outdoor unit (Tho-S). 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, suction gas in outdoor unit (Tho-S).

Part involved: S. fault Tho-S.

Likely causes:

Open/short circuit on sensor input; sensor does not work; 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

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 (printed 157) · Reviewed 23 September 2026

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

Reviewed: 23 September 2026