S.302 on a Vaillant heat pump: High-pressure switch open If the pressure in the refrigerant circuit exceeds the application limit, the heat pump is switched off for 15 minutes and is then restarted again. If the pressure remains too high after four unsuccessful restarts, the fault message F.731 is displayed
Short answer
On a Vaillant heat pump, S.302 means: High-pressure switch open If the pressure in the refrigerant circuit exceeds the application limit, the heat pump is switched off for 15 minutes and is then restarted again. If the pressure remains too high after four unsuccessful restarts, the fault message F.731 is displayed. The heat pump keeps running with some functions stopped. 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: High-pressure switch open If the pressure in the refrigerant circuit exceeds the application limit, the heat pump is switched off for 15 minutes and is then restarted again. If the pressure remains too high after four unsuccessful restarts, the fault message F.731 is displayed.
Part involved: Heat pump control (status/Live Monitor).
When it shows: High-pressure switch open If the pressure in the refrigerant circuit exceeds the application limit, the heat pump is switched off for 15 minutes and is then restarted again. If the pressure remains too high after four unsuccessful restarts, the fault message F.731 is displayed.
Likely causes:
- High-pressure switch open If the pressure in the refrigerant circuit exceeds the application limit, the heat pump is switched off for 15 minutes and is then restarted again. If the pressure remains too high after four unsuccessful restarts, the fault message F.731 is displayed.
On the flexoTHERM exclusive (VWF ../4)
The manual says: High-pressure switch open.
Part involved: Heat pump control (status/Live Monitor).
When it shows: See official description.
Likely causes:
- High-pressure switch open.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
The manual says: High pressure switch opened.
Part involved: Heat pump control (status/Live Monitor).
When it shows: See official description.
Likely causes:
- High pressure switch opened.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - status changes automatically with operating state.
Manual reset: not applicable.
What you can check
- Note the status code (Live Monitor). The heat pump will normally retry automatically; if a related F-code appears or heating/hot water stops, contact your installer.
What the engineer will check
- Read Live Monitor status and fault history; if the status persists or precedes an F-code, follow the corresponding F-code diagnostics in the installer fault table.
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
8 owner and engineer reports mention this.
- Keeps stopping / cutting out on the aroTHERM plus (VWL ../6 A): 6 reports
- Intermittent fault on the aroTHERM plus (VWL ../6 A): 2 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.58; VWZ MEH 97/6 hydraulic station 0020291544_03 p.50; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.55 · 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.49; flexoTHERM 230 V 0020213395_04 p.44 · Reviewed 23 September 2026
- geoTHERM mini VWS 36/4.1 230 V installation manual ↗ · 0020250181_00 · page geoTHERM mini 0020250181_00 p.36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026