Jacuzzi Z Builder Series Mechanics And Repair page 53

PC Board turned on heater without water flow which requires replacing the
PC board, or
Not enough water is moving over the element which is a flow problem, many
times due to dirty filters, or
Failed sensor
Flashing More On then Off:
Meaning: PC Board sees a sensor failure. Isolate which sensor and replace. Also
may occur if PC Board has failed.