F.086 on a Vaillant aroTHERM: Surface-mounted thermostat opened
Short answer
On a Vaillant heat pump, F.086 means: Surface-mounted thermostat 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: Surface-mounted thermostat opened.
Part involved: Surface-mounted thermostat opened.
Likely causes:
- Underfloor heating temperature too high; heating circuit flow rate too low; underfloor heating circuit closed.
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: 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 underfloor heating manifold/zone valves are open and the room thermostats are calling for heat. Contact your installer or Vaillant Service; do not attempt any repair.
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: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS installer certification; Vaillant product training recommended.
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.32; VWL ../2 A 0020147164_09 p.34 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026