Safety: Disconnect power before accessing the control board.

Power reset: Turn off power at the breaker for at least 5 minutes to allow the control to fully discharge. Restore power and check if E0 clears.
Check model configuration: If the indoor PCB was recently replaced, verify that the correct Vaillant board part number is installed for your model and that any DIP switches or configuration jumpers are set according to the service manual.
Inspect PCB: Remove the indoor electrical cover and visually inspect the PCB for burn marks, corrosion, or insect damage. Clean light dust with a dry brush; do not use water.
Firmware/config reset: Some Vaillant remotes allow a factory reset sequence (refer to the user manual). Perform a reset if available.
Board replacement: If E0 persists, the indoor main PCB is likely defective and must be replaced with an identical Vaillant part. Label and photograph all connections before swapping boards.

Due to the risk of mis‑wiring and configuration errors, PCB replacement is best handled by an authorized Vaillant technician.

E0 error, unit will not start or stops immediately after power‑up

Possible Causes