EC on a Mitsubishi Electric heat pump: Start time exceeded: outdoor microcomputer cannot receive communication
Short answer
On a Mitsubishi Electric heat pump, EC means: Start time exceeded: outdoor microcomputer cannot receive communication. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 9 sources
What it means
On the Ecodan Co2 Quhz
The manual says: Start time exceeded: outdoor microcomputer cannot receive communication.
Part involved: Cylinder unit-outdoor power/transmission line.
When it shows: Inability to receive communication detected on outdoor unit microcomputer.
Likely causes:
- 1 Defective power transmission line connection; 2 Defective outdoor inverter PCB; 3 Defective cylinder unit control board; 4 Noise.
On the Ecodan Puhz Sw Split
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan Puhz W Monobloc
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan R290 Puz Wz
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan R32 Puz Wm
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan R32 Zubadan Puz Hwm
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan Ultra Quiet Puhz W Vaa
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan Zubadan Puhz Hw Monobloc
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
On the Ecodan Zubadan Puhz Shw Split
The manual says: Startup time over: the unit cannot finish its startup process within 4 minutes after power on.
Part involved: Indoor (FTC)/outdoor connecting wire.
When it shows: Startup process not finished within 4 minutes of power-on.
Likely causes:
- 1 Contact failure of indoor/outdoor connecting wire; 2 Wire diameter or length out of specification; 3 Refrigerant address 0 used on slave unit (multiple outdoor units control); 4 Noise on power supply or connecting wire.
Is it safe?
On the Ecodan Co2 Quhz
| 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.
Manual reset: Outdoor error cancelled by switching the cylinder unit earth leakage circuit breaker OFF, waiting until the outdoor board LEDs go out (about 1 minute), then ON again (service manual GHH15010).
On the Ecodan Puhz Sw Split
| 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.
On the Ecodan Puhz W Monobloc
| 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.
On the Ecodan R290 Puz Wz
| 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.
On the Ecodan R32 Puz Wm
| 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.
On the Ecodan R32 Zubadan Puz Hwm
| 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.
On the Ecodan Ultra Quiet Puhz W Vaa
| 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.
On the Ecodan Zubadan Puhz Hw Monobloc
| 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.
On the Ecodan Zubadan Puhz Shw Split
| 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
On the Ecodan Co2 Quhz
- 1 Correct power transmission line connection; 2 Replace outdoor inverter PCB; 3 Replace cylinder unit control board; 4 Move power signal line away from noise source.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Puhz Sw Split
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Puhz W Monobloc
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan R290 Puz Wz
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan R32 Puz Wm
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan R32 Zubadan Puz Hwm
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Ultra Quiet Puhz W Vaa
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Zubadan Puhz Hw Monobloc
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and replace boards if it recurs.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Zubadan Puhz Shw Split
- As EA: check connecting wire, wire size/length, refrigerant address settings, noise; power off/on and 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 QUHZ-W40VA Service Manual (GHH15010) ↗ · GHH15010 · page 15 · Reviewed 23 September 2026
- 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