F.537 on a Vaillant aroTHERM: High-pressure switch opened
Short answer
On a Vaillant heat pump, F.537 means: High-pressure switch opened. 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: High-pressure switch opened.
Part involved: High-pressure switch opened.
Likely causes:
- Refrigerant volume too high or too low; insufficient vacuum; non-condensables; pressure switch or connection defective; loss of charge; flow rate too high; flow monitor defective; poor heat transfer in heat exchanger.
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 - the fault remains displayed until the cause is eliminated.
Manual reset: yes - after the cause is eliminated, press the reset button (indoor unit) or reset via the system control; if it recurs after several resets contact customer service.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). Check the outdoor unit's air inlet and outlet are not blocked by leaves, debris, snow or ice build-up and clear any loose debris from around it (do not open the casing, poke the fins or use tools). Do not keep resetting the unit; report the code to your installer (the operating instructions for this product were not checked for a homeowner reset procedure). If you smell gas/solvent near the outdoor unit or hear hissing, switch the heat pump off at the isolator, keep ignition sources away and call an engineer.
What the engineer will check
- Diagnose per cause list in the aroTHERM installer fault table; inform Vaillant technical support (0330 100 3540) for refrigerant-circuit faults.
Who to ask for: F-gas certified refrigeration engineer with heat pump experience (R290 flammable-refrigerant competence required for aroTHERM plus / GeniaAir).
Certification: F-gas Category I (Regulation (EU) 517/2014 as retained in GB) certificate; flammable (R290) refrigerant training for R290 units.
What you might notice
What owners and engineers report
2 owner and engineer reports mention this.
- No heating on the aroTHERM: 2 reports
Sources
- Installation instructions aroTHERM VWL 55/3 A 230 V, VWL 85/3 A 230 V (GB) ↗ · 0020217827_03 · page VWL ../3 A 0020217827_03 p.33; VWL ../2 A 0020147164_09 p.35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026