F.824 on a Vaillant aroTHERM plus: Building circuit : Brinepressure too low
Short answer
On a Vaillant heat pump, F.824 means: Building circuit : Brinepressure 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: Building circuit : Brinepressure too low.
Part involved: Brinepressure too low.
Likely causes:
- Note Can only occur in conjunction with an installed and activated intermediate heat exchanger set. Fault refers to the outdoor unit's brine pressure sensor; Pressure loss in the building circuit due to leakages or air pockets; Building circuit pressure 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). Read the heating system pressure on the display (Menu > Live Monitor > building circuit pressure) or the pressure gauge: it should be about 1.0-1.5 bar when cold. Vaillant's operating instructions say to inform your competent person so that they can top up the heating water. Check the filling loop valves are closed and look for visible water leaks or a dripping pressure-relief pipe.
What the engineer will check
- Check the building circuit for leaks; Top up with water, purge; Check the quality of the plug contact on the PCB and on the wiring harness; Check that the pressure sensor is working correctly; Replace the pressure 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
What owners and engineers report
16 owner and engineer reports mention this.
- No heating on the aroTHERM plus (VWL ../6 A): 8 reports
- No hot water on the aroTHERM plus (VWL ../6 A): 5 reports
- Pressure keeps dropping on the aroTHERM plus (VWL ../6 A): 3 reports
Sources
- uniTOWER (VIH QW 190/6 E) operating, installation and maintenance instructions ↗ · 0020291525_05 · page uniTOWER VIH QW 190/6 E 0020291525_05 p.63 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026