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

14Mitsubishi Heavy Industries Air-Conditioning Europe · Hydrolution HM gen 1 (HMA100V/HMS140V integrated-controller systems)

14 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution HM gen 1: Occurs if alarm 70 or 77 occurs 10 times continuously during defrost operation

Short answer

On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, 14 means: Occurs if alarm 70 or 77 occurs 10 times continuously during defrost operation. 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: Occurs if alarm 70 or 77 occurs 10 times continuously during defrost operation.

Part involved: Aborted defrost.

When it shows: 10 consecutive aborted defrosts.

Likely causes:

Refrigerant leakage; improper installation place of outdoor unit; insufficient water flow.

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 radiator/underfloor thermostats in the house are not all closed (user manual). 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

Indoor-unit checks per HM-T-193 flowchart: check sensors BT12/BT15/BT3, water-side service valves, valves QM31/QN11, strainer, air bleed, circulation pump setting (menu 2.2.5) and relay board AA6; check refrigerant charge/leaks for defrost alarms.

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.155; flowchart p.167 · Reviewed 23 September 2026

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

Reviewed: 23 September 2026