F.526 on a Glow-worm GeniaAir: The signal for the temperature sensor at the evaporator inlet in the refrigerant circuit is invalid
Short answer
On a Glow-worm heat pump, F.526 means: The signal for the temperature sensor at the evaporator inlet in the refrigerant circuit is invalid. 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: The signal for the temperature sensor at the evaporator inlet in the refrigerant circuit is invalid.
Part involved: The signal for the temperature sensor at the evaporator inlet in the refrigerant.
Likely causes:
- Temperature sensor not connected or sensor input has short-circuited.
- Glow-worm trade page: Evaporator inlet temperature sensor fault Fault in the electrical connection for the evaporator inlet temperature sensor, evaporator inlet temperature sensor defective.
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). Glow-worm's MiPro Sense operating instructions say always contact your competent person in the event of a fault message; until they arrive you may select a limp-home (back-up heater) setting on the control, which is expensive to run.
What the engineer will check
- Check: Plug, temperature sensor, wiring harness.
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
Sources
- GeniaAir Appliance Interface installation and maintenance instructions ↗ · 8000043014_01 · page HPIM 7 8000043014_01 p.31 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026