Nuevo EK 2 - problem with water heater

I have a 2-berth Nuevo EK (2010 ) bought new. My problem is that the Truma Ultrastore Water Heater does not work now when heating water via electricity. However, there is no such problem when using gas.
Does this mean that a fuse and/or electric heating element could be the cause? If yes, where would I find the relevant fuse and if it is the element, what would I be expected to pay for this to be replaced?
The Truma brochure indicates that there are two models of heaters available: 1) Ultrastore Rapid - 10 litres and 2) Ultrastore Rapid XL - 14 litres. Which type would have been fitted to my Nuevo?
Any comments, advice to help me solve this problem will be very much appreciated.

The power is via an 6A MCB on the Sargent PSU, with a isolation switch. Don't thing there is any further fusing.

Presumably you have checked the MCB and Isolation switch are on?