ED on a Mitsubishi Electric heat pump: Serial communication error between outdoor controller circuit board and outdoor power circuit board
Short answer
On a Mitsubishi Electric heat pump, ED means: Serial communication error between outdoor controller circuit board and outdoor power circuit board. 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: Serial communication error between outdoor controller circuit board and outdoor power circuit board.
Part involved: Outdoor controller board / power board (connectors CN2, CN4).
When it shows: Serial communication between outdoor controller board and outdoor power board defective.
Likely causes:
- 1 Wire breakage or contact failure of connector CN2 between outdoor controller and power boards; 2 Wire breakage or contact failure of connector CN4; 3 Defective communication circuit of outdoor power circuit board; 4 Defective communication circuit of outdoor controller board for power board.
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.
What the engineer will check
- 1-2 Check connection of connectors CN2 and CN4 between outdoor controller and power boards; 3 Replace outdoor power circuit board; 4 Replace outdoor controller circuit board.
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.29; OCH525C p.27 · Reviewed 23 September 2026
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.24; OCH605A p.21; OCH465D p.25; OCH439N p.60 · Reviewed 23 September 2026
- PUZ-WZ(85-100-120)(V-Y)AA(-BS) Service_Manual (OCH880) ↗ · OCH880 · page OCH880 p.44; OCH816 p.40 · Reviewed 23 September 2026
- Ecodan PUZ-WM(50-60-85-112)V(H-A)A Service Manual (OCH727A) ↗ · OCH727A · page 30 · Reviewed 23 September 2026
- Ecodan PUZ-HWM140(V-Y)HA Service Manual (OCH748A) ↗ · OCH748A · page 26 · Reviewed 23 September 2026
- PUHZ-W85-112VAA(-BS) Service Manual (OCH681) ↗ · OCH681 · page 21 · Reviewed 23 September 2026
- Ecodan PUHZ-HW140VHA2-BS / PUHZ-HW140YHA2-BS Service Manual (OCH439N) ↗ · OCH439N · page 60 · Reviewed 23 September 2026
- PUHZ-SHW112-140V/YHA Service Manual (OCH526) ↗ · OCH526 · page 31 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026