F.710 on a Vaillant heat pump: Env. circuit: Outlet temp. too low
Short answer
On a Vaillant heat pump, F.710 means: Env. circuit: Outlet temp. 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 flexoTHERM exclusive (VWF ../4)
The manual says: Env. circuit: Outlet temp. too low.
Part involved: Outlet temp. too low.
Likely causes:
- Environment circuit pump defective; Temperature sensor for environment circuit outlet defective; Volume flow too low in the environment circuit; Air in the environment circuit; Device Specific Number (DSN) setting was not applied when replacing the control PCB (HMU); Freeze protection setting was not applied when replacing the control PCB (HMU); Always check the Device Specific Number (DSN) setting.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
The manual says: Environment circuit: Outlet temperature too low.
Part involved: Outlet temperature too low.
Likely causes:
- Environment circuit pump defective; Temperature sensor for environment circuit outlet defective; Volume flow too low in the environment circuit; Air in the environment circuit.
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). Contact your installer or Vaillant Service; do not attempt any repair.
What the engineer will check
On the flexoTHERM exclusive (VWF ../4)
- Check the flow rate in the environment circuit; Check the quality of the plug contact on the PCB and on the cable harness; Check that the sensor is working correctly (resistance measurement using sensor characteristic values); Replace the sensor; Check the volume flow of the environment circuit pump (optimum spread of 3 K); Purge the environment circuit; Check the set value for the freeze protection in accordance with the environment circuit type on the control panel.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS ground-source installer; F-gas certificate for refrigerant work.
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
- Check the environment circuit flow rate; Check the quality of the plug contact on the PCB and on the cable harness; Check that the sensor is working correctly (measure the resistance using the sensor characteristic values in the appendix); Replace the sensor; Check the volume flow of the environment circuit pump (optimum spread of 3 K); Purging the environment circuit.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS ground-source installer; F-gas certificate for refrigerant work.
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.52; flexoTHERM 230 V 0020213395_04 p.47 · 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