my vaillant boiler is saying a code com on it ?

what do I do when your boiler says com on it an no heating or hot water
mel, December 2016


done
It refers to a communication fault between the two circuit boards, I believe the display actually reads CON? It could be a fatal board fault or a poor connection between the two, with the power off, try separating and reconnecting the boards

Carefree, December 2016
You do a Google search for - say "Valliant 'Model' Com Fault" but you replace 'Model' with the exact model number of your boiler.

XXX, December 2016
link Click here to see other fixes for Vaillant.