Suz

I have a Balboa VS501z that has no heat. Meter testing to the heater had normal results, the red heat light on the control panel is on but heat never reads more than 50. We replaced the heater, and still have no heat. System goes through priming, heat light comes on but we get no heat. Pulled the circuit board, and there are no burns. Entire system appears pristine, but we have no heat. Please help solve this mystery!