U7 on a Mitsubishi Electric heat pump: Too low superheat due to low discharge temperature
Short answer
On a Mitsubishi Electric heat pump, U7 means: Too low superheat due to low discharge temperature. 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: Too low superheat due to low discharge temperature.
Part involved: Discharge thermistor TH4 / linear expansion valve (LEV).
When it shows: Discharge superheat <= -15C continuously for 3 minutes even with LEV at minimum pulse, after 10 minutes of compressor operation.
Likely causes:
- 1 Disconnection or loose connection of discharge thermistor TH4; 2 Defective holder of discharge thermistor; 3 Disconnection or loose connection of LEV coil; 4 Disconnection or loose connection of LEV connector; 5 Defective linear expansion valve.
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
On the Ecodan Hydrodan
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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 Puhz Sw Split
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
- 1-2 Check installation of discharge thermistor TH4; 3 Check LEV coil; 4 Check LEV-A/LEV-B connectors on outdoor controller board; 5 Check linear expansion valve.
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
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.25; OCH525C p.23 · Reviewed 23 September 2026
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.20; OCH605A p.17; 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