Water Heater in Caravan keeps tripping out

Hi, we have a truma ultrastore water heater in our van which keeps tripping out the circuit breaker when we switch it on. We have checked that it is full of water. Could the element have gone? Also, when we use it on the gas, it clicks to ignite but then the red light comes on and locks out. We can smell the gas getting through, is this normal?

Any suggestions as to what could be the problem would be greatly appreciated