F.820 on a Vaillant aroTHERM plus: Connection fault: Building circuit pump
Short answer
On a Vaillant heat pump, F.820 means: Connection fault: Building circuit pump. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Connection fault: Building circuit pump.
Part involved: Building circuit pump.
Likely causes:
- Pump does not report any signal back to the heat pump.
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). Check that radiator/underfloor zone valves and thermostatic valves are not all closed and that the system control is calling for heat. The operating instructions allow the reset button on the indoor unit (or a reset via the system control) to be pressed once; if the code returns, do not keep resetting - contact your installer or Vaillant.
What the engineer will check
- Check the cable to the pump for defects and, if required, replace it; Replace the pump.
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
14 owner and engineer reports mention this.
- No heating on the aroTHERM plus (VWL ../6 A): 8 reports
- Keeps stopping / cutting out on the aroTHERM plus (VWL ../6 A): 6 reports
Sources
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.37; uniTOWER VIH QW 190/6 E 0020291525_05 p.63; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.60 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026