F.824 on a Glow-worm GeniaAir: Decoupling module (frost protection) brine circuit pressure too low
Short answer
On a Glow-worm heat pump, F.824 means: Decoupling module (frost protection) brine circuit pressure too low. 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: Decoupling module (frost protection) brine circuit pressure too low.
Part involved: Decoupling module (frost protection) brine circuit pressure too low.
Likely causes:
- No heating water in the decoupled building circuit or pressure too low (decoupling module for frost protection installed).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: likely clears when pressure restored (not stated in HPIM 7 doc).
Manual reset: not normally required.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). Read the system pressure (display/pressure gauge; normal cold 1.0-1.5 bar). Ask your installer to top up and find the cause of the pressure loss; check the filling loop is closed and look for visible leaks.
What the engineer will check
- Increase the pressure to above 0.5 bar and check it; check and, if required, replace the sensor.
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.34 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026