The new Thermo relief valve pulls all the air out of the thermal well first, which in turn creates higher head pressure for the pump, which in turn makes the seals last longer. Once all the air is pulled out of it, it pulls water out of the top, that way it isn't pulling sediment or hard water deposits that accumulate at the bottom of the thermal well.The thermol relief valve is on the bottom of the water tank and you plumb it to the top. In reality you are just recirculating the hot water back into the water box?
I had a 405 with 9500 hours and 6500 both ran great when I sold them.Derf..
You need to hire someone to be in charge of maintenance, bro