A fault has been detected by the control box during the pre-start diagnostic phase. In this instance you will need to contact your local Eberspacher dealership, who has the necessary diagnostic equipment to determine the actual reason for the heater not operating.
The same situation would also apply to Hydronic water heaters.Q6: I have just purchased a second hand heater, which I would like to change over the operating voltage? i.e. from 12V DC to 24V DC or 24V DC to 12V DC.