Bryan, I am assuming you have the Ultrastore water heater.
As for the electric tripping, it is more than likely the element is faulty, or a short circuit in the cable from the element to its switch(such as a staple through the cable)
On gas I assume you have removed the outer cover before trying to light the boiler.
If so, have you checked that there is gas available in the cylinder, the isolation tap to the heater is open and there is water in the unit?
If the answer to all those is yes, then iti will probably be a fault on the circuit board, get a Truma authorised engineer to check it all out.