Water Heaters - State Heater wont always lightup

My daughter and son-in-law live three hours from me and they have a five year old State 30 gal water heater in their new home that is scaling on the tank which drops onto the burner. When this happens, the unit will not fire up properly ans shuts down. She has to take a vaccum wand and remove the rust scale to get it to run. She has contacted the company and the contrator that put the unit in the new house and they say the unit is scaling due to it is too small of a unit for the four of them. Her two boys are only 5 and 7 years. The heater has an electronic controler on it and is a forced vented unit. Anyone with a simular problem and any perment fixes?

Here is what is happening: They use the entire contents of this too small heater almost every time they take a bath, shower, wash dishes and maybe even wash clothes. The tank then falls to the temperature of the incoming water and this cools the exhaust gases from the burner to the point the water vapor condenses on the cold tank and central flue. The water then causes the rust and scaling which breaks loose and falls onto the burner.

There is no cure other than installing a larger heater or using less hot water.

I got some numbers off the unit and I see it is a 40 gal not 30 as previously noted. It is P08640 NOVIT. I also have a State unit but it is not a NOVIT. The burner unit on hers is different than mine and looks more electronic. I do not have the problem with my burner and use it to fill a whirlpool unit quite regularly.