UF on a Mitsubishi Electric heat pump: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start
Short answer
On a Mitsubishi Electric heat pump, UF means: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start. 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
On the Ecodan Hydrodan
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Looseness, disconnection or reverse of compressor wiring; 3 Defective compressor; 4 Defective outdoor power board.
On the Ecodan Puhz Sw Split
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Looseness, disconnection or reverse of compressor wiring; 3 Defective compressor; 4 Defective outdoor power board.
On the Ecodan Puhz W Monobloc
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Compressor wiring loose/disconnected/reversed; 3 Defective compressor; 4 Defective outdoor power board; 5 Decreased water flow; 6 Clogged water filter; 7 Clogged plate heat exchanger; 8 Locked water pump; 9 Malfunction of water pump.
On the Ecodan R290 Puz Wz
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Compressor wiring loose/disconnected/reversed; 3 Defective compressor; 4 Defective outdoor power board; 5 DIP switch setting difference on outdoor controller board.
On the Ecodan R32 Puz Wm
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Looseness, disconnection or reverse of compressor wiring; 3 Defective compressor; 4 Defective outdoor power board.
On the Ecodan R32 Zubadan Puz Hwm
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Compressor wiring loose/disconnected/reversed; 3 Defective compressor; 4 Defective outdoor power board; 5 Decreased water flow; 6 Clogged water filter; 7 Clogged plate heat exchanger; 8 Locked water pump; 9 Malfunction of water pump.
On the Ecodan Ultra Quiet Puhz W Vaa
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Stop valve closed; 2 Decrease of power supply voltage; 3 Compressor wiring loose/disconnected/reversed; 4 Defective compressor; 5 Defective outdoor power board.
On the Ecodan Zubadan Puhz Hw Monobloc
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Compressor wiring loose/disconnected/reversed; 3 Defective compressor; 4 Defective outdoor power board; 5 Decreased water flow; 6 Clogged water filter; 7 Clogged plate heat exchanger; 8 Locked water pump; 9 Malfunction of water pump.
On the Ecodan Zubadan Puhz Shw Split
The manual says: Compressor overcurrent interruption (when compressor locked): overcurrent within 30 seconds of compressor start.
Part involved: Compressor / outdoor power circuit board.
When it shows: Overcurrent of DC bus or compressor within 30 s after compressor starts.
Likely causes:
- 1 Decrease of power supply voltage; 2 Looseness, disconnection or reverse of compressor wiring; 3 Defective compressor; 4 Defective outdoor power 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 Check power supply; 2 Correct compressor wiring (U-V-W); 3 Check compressor; 4 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 Check power supply; 2 Correct compressor wiring (U-V-W); 3 Check compressor; 4 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 Check power supply; 2 Correct compressor wiring; 3 Check compressor; 4 Replace power board; 5-9 Check water circuit and repair.
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 Check power supply; 2 Correct compressor wiring (U-V-W); 3 Check compressor; 4 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 Check power supply; 2 Correct compressor wiring (U-V-W); 3 Check compressor; 4 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 Check power supply; 2 Correct compressor wiring; 3 Check compressor; 4 Replace power board; 5-9 Check water circuit and repair.
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; 3 Correct compressor wiring (U-V-W); 4 Check compressor; 5 Replace outdoor power 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 Check power supply; 2 Correct compressor wiring; 3 Check compressor; 4 Replace power board; 5-9 Check water circuit and repair.
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 Check power supply; 2 Correct compressor wiring (U-V-W); 3 Check compressor; 4 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 51 (PDF p.52) · Reviewed 23 September 2026
- Ecodan PUHZ-SW(75-100-120)(V-Y)HA-BS Service Manual (OCH755) ↗ · OCH755 · page OCH755 p.27; OCH525C p.25 · Reviewed 23 September 2026
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.22; OCH605A p.19; OCH465D p.24; OCH439N p.58 · Reviewed 23 September 2026
- PUZ-WZ(85-100-120)(V-Y)AA(-BS) Service_Manual (OCH880) ↗ · OCH880 · page OCH880 p.41; OCH816 p.37 · Reviewed 23 September 2026
- Ecodan PUZ-WM(50-60-85-112)V(H-A)A Service Manual (OCH727A) ↗ · OCH727A · page 28 · Reviewed 23 September 2026
- Ecodan PUZ-HWM140(V-Y)HA Service Manual (OCH748A) ↗ · OCH748A · page 25 · Reviewed 23 September 2026
- PUHZ-W85-112VAA(-BS) Service Manual (OCH681) ↗ · OCH681 · page 19 · Reviewed 23 September 2026
- Ecodan PUHZ-HW140VHA2-BS / PUHZ-HW140YHA2-BS Service Manual (OCH439N) ↗ · OCH439N · page 58 · Reviewed 23 September 2026
- PUHZ-SHW112-140V/YHA Service Manual (OCH526) ↗ · OCH526 · page 29 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026