One problem you may encounter is that the heater is not getting any gas or spark. First check to see that the heater is getting enough voltage and that the battery is good. If that is not the cause check to see if you have a bad thermal cup that needs to be replaced. Another reason could be a defective on/off switch not allowing anything to work; try replacing it. If it is not any of these causes, the thermostat could be broken and not registering, or the circuit board could be bad. These problems can be fixed by replacing them.
Another problem that may occur is the water temperature is either too hot or cold. A bad thermostat on the heater might be setting the temperature to high or too low; try replacing it. If the thermostat isn't seated correctly, it should be replaced. It is possible that the bypass kit for the water heater valve doesn't set properly. You must move the bypass valve into proper position. If everything else is working correctly, these steps should fix the water temperature problem.
One more problem you may encounter is that the ignitor fails to light or intermittently doesn't light. The ceramic electrode might be cracked and should be replaced, and this means that the thermostat isn't working properly and should be replaced as well. Another quick fix may be tightening or replacing the ground screw. There may also be a ground wire at the top of the circuit board that could be loose, so try tightening this. Finally, it could be caused by a poor ground at the electrodes. You might have to loosen the electrode attachment screw and re-tighten it.
