UD on a Mitsubishi Electric heat pump: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation
Short answer
On a Mitsubishi Electric heat pump, UD means: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation. 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
On the Ecodan Puhz Sw Split
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller board.
On the Ecodan Puhz W Monobloc
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller board.
On the Ecodan R290 Puz Wz
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller board.
On the Ecodan R32 Puz Wm
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller board.
On the Ecodan R32 Zubadan Puz Hwm
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan or short cycle during cooling; 2 Defective TH3; 3 Defective outdoor controller board; 4 Defective pressure sensor 63HS.
On the Ecodan Ultra Quiet Puhz W Vaa
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller board.
On the Ecodan Zubadan Puhz Hw Monobloc
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan or short cycle during cooling; 2 Defective TH3; 3 Defective outdoor controller board; 4 Defective pressure sensor 63HS.
On the Ecodan Zubadan Puhz Shw Split
The manual says: Overheat protection: outdoor liquid pipe TH3 or condensing temperature (63HS) >= 70C during compressor operation.
Part involved: Liquid thermistor TH3 / pressure sensor 63HS.
When it shows: TH3 or T63HS >= 70C during compressor operation.
Likely causes:
- 1 Defective outdoor fan (fan motor) or short cycle of outdoor unit during cooling; 2 Defective TH3 / condensing temperature T63HS; 3 Defective outdoor controller 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. Also check from a distance that the outdoor unit air inlet/outlet is not blocked by snow, ice, leaves or other debris (never reach into the fan).
What the engineer will check
On the Ecodan Puhz Sw Split
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R410A).
On the Ecodan Puhz W Monobloc
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R410A).
On the Ecodan R290 Puz Wz
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification plus competence for flammable A3 refrigerant (R290).
On the Ecodan R32 Puz Wm
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R32, A2L mildly flammable).
On the Ecodan R32 Zubadan Puz Hwm
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R32, A2L mildly flammable).
On the Ecodan Ultra Quiet Puhz W Vaa
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R410A).
On the Ecodan Zubadan Puhz Hw Monobloc
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R410A).
On the Ecodan Zubadan Puhz Shw Split
- 1 Check outdoor unit air passage; 2-3 Power off/on and recheck code; if U4 displayed follow U4.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas).
Certification: UK F-gas Category I certification (R410A).
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Keeps stopping / cutting out on the Ecodan R32 Puz Wm: 1 report
Sources
- 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