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Heat pumps · Error codes · Mitsubishi Electric
EAMitsubishi Electric

EA on a Mitsubishi Electric heat pump: Indoor/outdoor unit connector miswiring, excessive number of units (2 units or more): outdoor board cannot confirm number of connected FTC/indoor units within 4 minutes of power-on

Short answer

On a Mitsubishi Electric heat pump, EA means: Indoor/outdoor unit connector miswiring, excessive number of units (2 units or more): outdoor board cannot confirm number of connected FTC/indoor units within 4 minutes of power-on. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 8 sources

What it means

The manual says: Indoor/outdoor unit connector miswiring, excessive number of units (2 units or more): outdoor board cannot confirm number of connected FTC/indoor units within 4 minutes of power-on.

Part involved: Indoor (FTC)/outdoor connecting wire S1-S2-S3.

When it shows: Number of connected indoor units cannot be checked automatically 4 minutes after power-on, or recognised as 2 or more.

Likely causes:

  • 1 Contact failure or miswiring of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 2 or more indoor units/FTCs connected to one outdoor unit; 4 Defective transmitting/receiving circuit of outdoor controller board; 5 Defective transmitting/receiving circuit of indoor controller board; 6 Defective indoor power board; 7 Refrigerant address 0 used on a slave outdoor unit (multiple outdoor units control, address range 1-6); 8 Noise on power supply or connecting wire.

Is it safe?

Does the heat pump stop?Yes
SeverityFault — 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: Not stated as auto-recovering in the service manual; code is logged in the outdoor unit error history.

Manual reset: Clear via RESET on the main remote controller after the cause is fixed; service manual actions include switching power off and on to recheck.

What you can check

  • Note the code, unit and ref. address shown on the main remote controller and contact your installer (Mitsubishi user manuals: 'Make a note of the error code number and contact installer'). Check the heat pump breaker/isolator at the consumer unit is on and read the primary system pressure gauge (if fitted) so you can report it. A single reset from the main remote controller (RESET, then Yes) may be tried; if the code returns, do not keep resetting. Do not open the outdoor unit, cylinder/hydrobox or any casing. A power cycle is a Mitsubishi first step for communication codes: switching the heat pump off and on at its isolator (outdoor and indoor supplies) once is acceptable.

What the engineer will check

  • 1 Check disconnection/looseness/polarity of indoor-outdoor wire; 2 Check wire size and length (total 80 m max) and S1,S2,S3 order; 3 Check number of indoor units per outdoor unit; 4-6 Power off/on and recheck, replace outdoor/indoor controller board or indoor power board if it recurs; 7 Check refrigerant address switches SW1-3 to SW1-6 for overlap; 8 Check transmission path for noise.

Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).

What you might notice

What owners and engineers report

1 owner and engineer report mentions this.

  • Heat pump will not start on the Ecodan Puhz W Monobloc: 1 report

Sources

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

Reviewed: 23 September 2026