757 on an alpha innotec heat pump: Low-pressure fault in W/W-appliance: Low-pressure pressostat in a water/water unit triggered repeatedly or for more than 20 s. After three occurrences the installation can only be cleared by authorised service personnel
Short answer
On an alpha innotec heat pump, 757 means: Low-pressure fault in W/W-appliance: Low-pressure pressostat in a water/water unit triggered repeatedly or for more than 20 s. After three occurrences the installation can only be cleared by authorised service personnel. 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: Low-pressure fault in W/W-appliance: Low-pressure pressostat in a water/water unit triggered repeatedly or for more than 20 s. After three occurrences the installation can only be cleared by authorised service personnel.
When it shows: Low-pressure pressostat in a water/water unit triggered repeatedly or for more than 20 s. After three occurrences the installation can only be cleared by authorised service personnel.
Likely causes:
- Low pressure in refrigerant circuit of water/water unit.
Is it safe?
| 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: no.
Manual reset: manual reset by installer/authorised service required.
What you can check
- Note the error number and text shown on the Luxtronik display.
- Acknowledge the message by pressing the rotary pushbutton for about 7 seconds (as the Luxtronik manual permits); if the same error reappears, contact your installer or ait customer service with the error number.
- Check the heat pump breakers/isolator at the consumer unit are on (do not open any casing).
What the engineer will check
- Investigate low-pressure cause; clearance only by authorised service personnel after 3 occurrences.
Who to ask for: F-gas certified refrigeration / heat pump engineer (R290 flammable-refrigerant competence for propane units such as LWD).
Certification: F-gas certification (R407C/R410A units); flammable refrigerant training for R290 units.
What you might notice
Sources
- Operating manual Luxtronik heating and heat pump control Part 2 (UK) 83055400lUK - 2.1 ↗ · 83055400lUK 2.1 · page 53 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026