F.022 on a Vaillant heat pump: Building circuit: Water press. too low
Short answer
On a Vaillant heat pump, F.022 means: Building circuit: Water press. too low. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the aroTHERM plus (VWL ../6 A)
The manual says: Building circuit: Water press. too low.
Part involved: Water press. too low.
When it shows: Filling pressure below 0.05 MPa (0.5 bar) for longer than one minute; F.22 alternates with the current pressure on the display (M.32 appears below 0.7 bar first).
Likely causes:
- Pressure loss in the building circuit due to leakages or air pockets; Building circuit pressure sensor defective.
On the aroTHERM
The manual says: Water pressure too low.
Part involved: Water pressure too low.
Likely causes:
- Insufficient water in the heating system.
Is it safe?
On the aroTHERM plus (VWL ../6 A)
| 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: yes - clears when the filling pressure rises above 0.5 bar (or the blocking time elapses).
Manual reset: not required once pressure is restored.
On the aroTHERM
| 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).
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
On the aroTHERM plus (VWL ../6 A)
- 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.
On the aroTHERM
- Check heating circuit for leaks/air, top up and purge; check expansion vessel; check pressure sensor and wiring.
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
18 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
- No heating on the aroTHERM: 2 reports
Sources
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.34; uniTOWER VIH QW 190/6 E 0020291525_05 p.59; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.57 · Reviewed 23 September 2026
- 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