Water Heater not working

I had to return my 2017 Symbol to the supplying dealer recently because of an error message on the Truma control unit which turned out to be a blown fuse stopping mains electric heater and hot water working.  Just tried to use it for the first time and the error message has gone and  the heater is working perfectly but no hot water.   Any ideas ?  Many thanks.  Bill

Don’t say which model you have fitted but I believe same element is used for both tasks, so if heating is on,water should also heat up IF boiler is full of water. Water would heat much quicker without heating saping away the heat.
May take some time to heat water with heating on. 
Are you sure hot tank is full and have you allowed sufficient time for water to heat, also did the dealer test all ok after chargeing fuse ?

If the hot water has a 'boost' setting use it.  It will temporarily stop the Combi heating the motorhome and so concentrate the heat on the hot water water tank.

Is the dump valve open? If it is, you will have lost your water.

The OP has said 'no hot water'.  Does he mean when the hot tap is opened no water flows, or, water flows but it isn't hot?  I have assumed the latter.  If the dump valve is open the water pump will run continuously whether the taps are open or not.  If he hasn't filled the hot water tank fully, every time he opens a hot water tap it will fill a bit more until it is eventually full and water will flow.

Bill ??

Thank you for the replies which were appreciated.  It was my fault en tirely as I was just not leaving the hot water on long enough when I had the heater on and eventually it came hot !  Many thanks.  Bill