PE on a Mitsubishi Electric heat pump: Inlet water temperature abnormality (return water THW2 too cold during compressor operation)
Short answer
On a Mitsubishi Electric heat pump, PE means: Inlet water temperature abnormality (return water THW2 too cold 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 · 6 sources
What it means
On the Ecodan Puhz W Monobloc
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling TH32 (inlet water) < 3C; heating TH32 < -10C; defrost TH32 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
On the Ecodan R290 Puz Wz
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling THW2 < 3C; heating (excl. defrost) THW2 < -10C; defrost THW2 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
On the Ecodan R32 Puz Wm
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling THW2 < 3C; heating (excl. defrost) THW2 < -10C; defrost THW2 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
On the Ecodan R32 Zubadan Puz Hwm
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling THW2 < 3C; heating (excl. defrost) THW2 < -10C; defrost THW2 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
On the Ecodan Ultra Quiet Puhz W Vaa
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling TH34 (inlet water) < 3C; heating TH34 < -10C; defrost TH34 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
On the Ecodan Zubadan Puhz Hw Monobloc
The manual says: Inlet water temperature abnormality (return water THW2 too cold during compressor operation).
Part involved: Return water thermistor THW2 / water circuit.
When it shows: For 10 s during compressor operation: cooling TH32 (inlet water) < 3C; heating TH32 < -10C; defrost TH32 < 0C.
Likely causes:
- 1 Reduced water flow (clogged filter, water leak); 2 Low temperature (low load, low inlet water temperature); 3 Defective water pump; 4 Leakage or shortage of refrigerant.
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. Check the primary circuit pressure gauge (typically about 1-2 bar when cold on sealed systems) and look for visible leaks; do not top up or bleed unless your installer has shown you how and the filling loop is then closed.
What the engineer will check
On the Ecodan Puhz W Monobloc
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification (R410A) (if refrigerant circuit work is needed).
On the Ecodan R290 Puz Wz
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification plus competence for flammable A3 refrigerant (R290) (if refrigerant circuit work is needed).
On the Ecodan R32 Puz Wm
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification (R32, A2L mildly flammable) (if refrigerant circuit work is needed).
On the Ecodan R32 Zubadan Puz Hwm
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification (R32, A2L mildly flammable) (if refrigerant circuit work is needed).
On the Ecodan Ultra Quiet Puhz W Vaa
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification (R410A) (if refrigerant circuit work is needed).
On the Ecodan Zubadan Puhz Hw Monobloc
- 1-2 Check water piping; 3 Check water pump; 4 Check intake superheat and refrigerant leakage.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (refrigeration / F-gas) / heating engineer (water circuit).
Certification: UK F-gas Category I certification (R410A) (if refrigerant circuit work is needed).
What you might notice
Sources
- Ecodan PUHZ-W112VHA-BS Service Manual (OCH562D) ↗ · OCH562D · page OCH562D p.25; OCH605A p.22; OCH465D p.27; OCH439N p.61 · Reviewed 23 September 2026
- PUZ-WZ(85-100-120)(V-Y)AA(-BS) Service_Manual (OCH880) ↗ · OCH880 · page OCH816 p.41 · Reviewed 23 September 2026
- Ecodan PUZ-WM(50-60-85-112)V(H-A)A Service Manual (OCH727A) ↗ · OCH727A · page 31 · Reviewed 23 September 2026
- Ecodan PUZ-HWM140(V-Y)HA Service Manual (OCH748A) ↗ · OCH748A · page 27 · Reviewed 23 September 2026
- PUHZ-W85-112VAA(-BS) Service Manual (OCH681) ↗ · OCH681 · page 22 · Reviewed 23 September 2026
- Ecodan PUHZ-HW140VHA2-BS / PUHZ-HW140YHA2-BS Service Manual (OCH439N) ↗ · OCH439N · page 61 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026