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This video advises that in cool weather you turn on the Webasto when you leave home and turn it off when you get back. I now do this, just turning the thermostat down to 14C overnight and 18-20 when we are up.
This video describes how to use diluted vinegar to descale the boiler. Citric acid has been recommended in the past but several members have had floods as citric acid can dissolve the aluminium welding, so avoid!
Thanks to Steve Sykes for pointing out the full list of Webasto information