U6 on a Mitsubishi Electric heat pump: Power module abnormality: checked by driving power module when overcurrent detected (UF or UP condition)
Short answer
On a Mitsubishi Electric heat pump, U6 means: Power module abnormality: checked by driving power module when overcurrent detected (UF or UP condition). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 9 sources
What it means
The manual says: Power module abnormality: checked by driving power module when overcurrent detected (UF or UP condition).
Part involved: Inverter power module (outdoor power circuit board) / compressor.
When it shows: Abnormality found when driving power module after overcurrent (UF or UP condition).
Likely causes:
- 1 Outdoor stop valve closed; 2 Decrease of power supply voltage; 3 Looseness, disconnection or reverse of compressor wiring; 4 Defective compressor; 5 Defective outdoor power circuit board.
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| 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. Do not reset repeatedly: this is an electrical/compressor protection code. If the breaker or RCD has tripped, or there is a burning smell, leave the heat pump switched off at its isolator and call an engineer. Do not open any casing.
What the engineer will check
On the Ecodan Hydrodan
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R32, A2L mildly flammable).
On the Ecodan Puhz Sw Split
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R410A).
On the Ecodan Puhz W Monobloc
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R410A).
On the Ecodan R290 Puz Wz
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification plus competence for flammable A3 refrigerant (R290).
On the Ecodan R32 Puz Wm
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R32, A2L mildly flammable).
On the Ecodan R32 Zubadan Puz Hwm
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R32, A2L mildly flammable).
On the Ecodan Ultra Quiet Puhz W Vaa
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R410A).
On the Ecodan Zubadan Puhz Hw Monobloc
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R410A).
On the Ecodan Zubadan Puhz Shw Split
- 1 Open stop valve; 2 Check power supply facility; 3 Correct compressor wiring (U-V-W phase); 4 Check compressor (winding resistance/insulation); 5 Replace outdoor power circuit board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience; UK F-gas Category I certification (R410A).
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 Hydrodan EHWT17D-MHEDW Installation Manual RK79D203K04 ↗ · RK79D203K04 · page 50 (PDF p.51) · Reviewed 23 September 2026
- Ecodan PUHZ-SW(75-100-120)(V-Y)HA-BS Service Manual (OCH755) ↗ · OCH755 · page OCH755 p.25; OCH525C p.23 · Reviewed 23 September 2026
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.20; OCH605A p.17; OCH465D p.22; OCH439N p.56 · Reviewed 23 September 2026
- PUZ-WZ(85-100-120)(V-Y)AA(-BS) Service_Manual (OCH880) ↗ · OCH880 · page OCH880 p.39; OCH816 p.35 · Reviewed 23 September 2026
- Ecodan PUZ-WM(50-60-85-112)V(H-A)A Service Manual (OCH727A) ↗ · OCH727A · page 26 · Reviewed 23 September 2026
- Ecodan PUZ-HWM140(V-Y)HA Service Manual (OCH748A) ↗ · OCH748A · page 23 · Reviewed 23 September 2026
- PUHZ-W85-112VAA(-BS) Service Manual (OCH681) ↗ · OCH681 · page 17 · Reviewed 23 September 2026
- Ecodan PUHZ-HW140VHA2-BS / PUHZ-HW140YHA2-BS Service Manual (OCH439N) ↗ · OCH439N · page 56 · Reviewed 23 September 2026
- PUHZ-SHW112-140V/YHA Service Manual (OCH526) ↗ · OCH526 · page 27 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026