LU on a Mitsubishi Electric Ecodan Co2 Quhz: Water circulation pump failure (pump 1 or pump A PWM feedback 83-92% for 10 s)
Short answer
On a Mitsubishi Electric heat pump, LU means: Water circulation pump failure (pump 1 or pump A PWM feedback 83-92% for 10 s). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Water circulation pump failure (pump 1 or pump A PWM feedback 83-92% for 10 s).
Part involved: Water circulation pump 1 / pump A.
When it shows: PWM feedback signal 83-92% for 10 consecutive seconds while pump running (request code 576: 1 = pump 1, 2 = pump A).
Likely causes:
- 1 Power supply voltage increase; 2 Connector/terminal detached; 3 Pump locked; 4 Pump reaching end of life; 5 Pump fault; 6 FTC board failure.
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.
Manual reset: Press F4 (Reset) then F3 (Yes) on the main remote controller, or switch system off (installation manual).
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
- 1 Check supply voltage; 2 Check terminals/connectors; 3-5 Power indoor and outdoor units off/on; if LU persists replace pump (check for clogging by foreign material); 6 Replace board.
Who to ask for: Heat pump installer / heating engineer (hydraulic circuit).
What you might notice
Sources
- Ecodan EHPT20Q VM2EA Service Manual (GCH15010C) ↗ · GCH15010C · page 39 (10-4 Self diagnosis and action) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026