EB on a Mitsubishi Electric heat pump: Miswiring of indoor/outdoor unit connecting wire (reverse wiring or disconnection): indoor unit number cannot be set within 4 minutes of power-on
Short answer
On a Mitsubishi Electric heat pump, EB means: Miswiring of indoor/outdoor unit connecting wire (reverse wiring or disconnection): indoor unit number cannot be set 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: Miswiring of indoor/outdoor unit connecting wire (reverse wiring or disconnection): indoor unit number cannot be set within 4 minutes of power-on.
Part involved: Indoor (FTC)/outdoor connecting wire S1-S2-S3.
When it shows: Indoor unit number cannot be set within 4 minutes after power on because of reverse wiring or disconnection.
Likely causes:
- 1 Contact failure or miswiring of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Defective transmitting/receiving circuit of outdoor controller board; 4 Defective transmitting/receiving circuit of indoor controller board; 5 Defective indoor power board; 6 Refrigerant address 0 used on slave outdoor unit (multiple outdoor units control); 7 Noise on power supply or connecting wire.
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: 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
- As EA: check S1/S2/S3 wiring polarity and continuity, wire size/length, refrigerant address, power off/on, replace boards if it recurs.
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
- Ecodan PUHZ-SW(75-100-120)(V-Y)HA-BS Service Manual (OCH755) ↗ · OCH755 · page OCH755 p.23; OCH525C p.21 · Reviewed 23 September 2026
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.18; OCH605A p.15; OCH465D p.20; OCH439N p.54 · Reviewed 23 September 2026
- PUZ-WZ(85-100-120)(V-Y)AA(-BS) Service_Manual (OCH880) ↗ · OCH880 · page OCH880 p.37; OCH816 p.33 · Reviewed 23 September 2026
- Ecodan PUZ-WM(50-60-85-112)V(H-A)A Service Manual (OCH727A) ↗ · OCH727A · page 24 · Reviewed 23 September 2026
- Ecodan PUZ-HWM140(V-Y)HA Service Manual (OCH748A) ↗ · OCH748A · page 21 · Reviewed 23 September 2026
- PUHZ-W85-112VAA(-BS) Service Manual (OCH681) ↗ · OCH681 · page 15 · Reviewed 23 September 2026
- Ecodan PUHZ-HW140VHA2-BS / PUHZ-HW140YHA2-BS Service Manual (OCH439N) ↗ · OCH439N · page 54 · Reviewed 23 September 2026
- PUHZ-SHW112-140V/YHA Service Manual (OCH526) ↗ · OCH526 · page 25 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026