M.32 on a Vaillant heat pump: Building circuit: Waterpress. Low
Short answer
On a Vaillant heat pump, M.32 means: Building circuit: Waterpress. Low. The heat pump keeps running. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the aroTHERM plus (VWL ../6 A)
The manual says: Building circuit: Waterpress. Low.
Part involved: Waterpress. Low.
When it shows: Building circuit pressure falls below 0.07 MPa (0.7 bar); clears above 0.7 bar. The spanner symbol appears after about one minute.
Likely causes:
- Pressure loss in the building circuit due to leakages or air pockets; Building circuit pressure sensor is defective.
On the flexoTHERM exclusive (VWF ../4)
The manual says: Building circuit: Pressure low.
Part involved: Pressure low.
Likely causes:
- Pressure loss in the building circuit due to leakages or air pockets; Building circuit pressure sensor is defective.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
The manual says: Building circuit: Pressure low.
Part involved: Pressure low.
Likely causes:
- Pressure loss in the building circuit due to leaks or air pockets; Building circuit pressure sensor is defective.
Is it safe?
On the aroTHERM plus (VWL ../6 A)
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: yes - message clears when the condition is resolved (maintenance message reset by engineer via Installer level > Resets).
Manual reset: engineer resets maintenance message after work.
On the flexoTHERM exclusive (VWF ../4)
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: clears when condition resolved.
Manual reset: engineer resets maintenance message.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: clears when condition resolved.
Manual reset: engineer resets maintenance message.
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 heating water and purge; Check the plug contact on the PCB and on the wiring harness; check that the pressure sensor is working correctly and, if required, 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 flexoTHERM exclusive (VWF ../4)
- Check the building circuit for leaks, top up with heating water and purge; Check the plug contact on the PCB and on the cable harness; check that the pressure sensor is working correctly and, if required, 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 geoTHERM mini (VWS 30/4, VWS 36/4.1)
- Check the building circuit for leaks, top up with heating water and purge; Check the plug contact on the PCB and on the cable harness; check that the pressure sensor is working correctly and, if required, 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
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.33; uniTOWER VIH QW 190/6 E 0020291525_05 p.59; VWZ MEH 97/6 hydraulic station 0020291544_03 p.51; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.56 · Reviewed 23 September 2026
- flexoTHERM exclusive VWF 57/4 - 197/4 400V installation and maintenance instructions ↗ · 0020213394_05 · page flexoTHERM 400 V 0020213394_05 p.50; flexoTHERM 230 V 0020213395_04 p.45 · Reviewed 23 September 2026
- geoTHERM mini VWS 36/4.1 230 V installation manual ↗ · 0020250181_00 · page geoTHERM mini 0020250181_00 p.35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026