[JRTJH]

I've seen more than one water heater igniter that will ground out and stop sparking once the water heater gets warm. I'd guess it's possible that one might well "ground out when cold and then start working when it gets hot"... Seems (to me) that as the metal gets hot, it expands just enough to "torque the igniter element, causing it to bend and ground out".... Might be worth a look to see if yours is shorting to ground. It'll still "click like it's sparking" but the spark is going to ground, not to the ends of the two elements and sparking between them.