F.702 on a Vaillant heat pump: Sensor fault: Env. circuit outlet temp
Short answer
On a Vaillant heat pump, F.702 means: Sensor fault: Env. circuit outlet temp. 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 flexoTHERM exclusive (VWF ../4)
The manual says: Sensor fault: Env. circuit outlet temp.
Part involved: Env. circuit outlet temp.
Likely causes:
- Sensor not connected or sensor input has short-circuited.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
The manual says: Temp. sensor fault: Environment cir. out.
Part involved: Environment cir. out.
Likely causes:
- Sensor not connected or sensor input has short-circuited (shared table row).
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). Do not keep resetting the unit; report the code to your installer (the operating instructions for this product were not checked for a homeowner reset procedure).
What the engineer will check
On the flexoTHERM exclusive (VWF ../4)
- Check the sensor, and replace if necessary; Replace the cable harness.
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 and, if required, replace the sensor (resistance vs sensor characteristic values in the appendix); Replace the cable harness.
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
- flexoTHERM exclusive VWF 57/4 - 197/4 400V installation and maintenance instructions ↗ · 0020213394_05 · page flexoTHERM 400 V 0020213394_05 p.51; flexoTHERM 230 V 0020213395_04 p.46 · Reviewed 23 September 2026
- geoTHERM mini VWS 36/4.1 230 V installation manual ↗ · 0020250181_00 · page geoTHERM mini 0020250181_00 p.37 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026