What is going on?

[aylad]

The pump does not fill up all the way

Just another thought--is the water level up high enough for the pump to prime? Also, have you tried a "snake" in the return lines to check for a blockage?

Janet

[flyboy320]

The heater won't be turning on probably because there is little to no flow of water through it. It's a safety feature of the heater, if it detects no water flow/pressure, it won't light so as not to burn up, since the water flowing through it is what keeps it cool.