Plumbing Questions? Ask a Plumber and Get Answers ASAP.
I need the brand name that goes with the model number.
Tell me about how old the unit is also please.
Next turn on the shower, set to its hottest setting, and then turn the kitchen sink hot tap and tell me if you still get suddenly cold water or not.
We can go from there.
There is a 'flow switch' in the water heater, that will turn off the heater if the water flow drops below its set point, at around 0.75 gallons per minute. That switch can also stick, due to water scale build up in the piston mechanism.
So that depending on the hot water flow at any given instant, and the random sticking of the flow switch piston... the burners will shut off.
In some areas with hard water the heat exchanger needs to be flushed with white vinegar for an hour or so to remove the hard water scale that is causing the flow switch to stick.
There is about a 95% chance my remarks are accurate...and a much lesser chance of an electronics anomally causing the problem.
You can have the water heater flushed for about $300 by a plumber, or you can do it yourself if you are handy, Let me know if you need coaching on that or not, I will submit a $20 offer that will include up to 4 hours on line coaching.