F.70 displayed after PCB replacement or power-up; appliance may not operate correctly

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Incorrect PCB fitted for model, PCB not coded to appliance type, Incorrect parameter settings after board replacement

Safety: Isolate power before handling the PCB.

Verify part number: Check that the installed PCB matches the exact Vaillant model and GC number of the water heater.
Configure PCB: Use Vaillant’s service mode to set the correct appliance type and parameters as described in the service manual.
Reset fault: After correct configuration, reset the appliance and confirm that F.70 clears.
Replace with correct board: If the PCB is the wrong type, fit the correct Vaillant board and repeat configuration.

Medium 3/5

Main Control PCB

Check Price on Amazon

We may earn a commission from links on this page.