We have a two hot water tank system and occasionally there will be no hot water. This seems to occur when the water has not been running for a while (like in the evening or first thing in the AM). The pilot light is on in both tanks and the burners are lit? Any idea why we don't have hot water at times?

How big is your house ? Seems like your bathroom is too far away from the heaters and it takes few minutes before hot water arrives... Also, it could be that second heater is not firing holding full tank of cold water.

Question: Does this happens all day long or in the morning only ? Do you have hot water circulating pump ? Timer on the pump ? How are these to heaters connected: in series or parallel ?

Back to you. Milo