Spa Doctor--Blows Onboard Fuse

The 20, 25, or 30a fuse are slow burning fuses. This means that they are designed to handle peak amp draws at the beginning of a cycle that drops dramatically quickly. Peaks are caused by the startup of a motor. We all have seen the lights dim when a motor starts. This is because of the initial draw of power. To compensate for this the main fuses are slow burning. They work fine until the motor draws too much amps initially and continually. Overdrawing motors cause almost all slow blowing fuses to blow.

If this happens you can confirm it's the moto. Turn off main power and replace fuse with like or less amperage. Now disconnect the pump(s) to the control box. Turn on power. If you can hear the pcboard going through it's steps, then you know the motor is the cause of failure. Again, 99% of the time fuse failure is caused by motors. Replace the motor and usually the pump also.