This is mother of all spa pool (בריכות ספא) problems. 99% of all problems arise due to lack of maintaining proper water chemistry in your spa pool.
2. Heater failure
Most heater failures are due to low ph in the water. Any ph under 7.0 for an extended amount of time will corrode the heating element to the point of failure. This will typically manifest as a tripped GFCI breaker and the results are mostly to replace the heating element or heater
3. Circulation pump failure
Many modern spas and hot tubs have a 24/7 circulation pump. Water chemistry problems coupled with pump seal failure is a common problem.
4. Flow or pressure switch problem
Both a flow switch or a pressure switch are mechanical components with a limit life cycle.
5. Burned circuit board
A burned circuit board is typically the result of loose heater terminal connection screws. After a few years, those screws tend to vibrate and loosen up the connection to the heater. This results in heat building up and transferring to the circuit board.
6. Mice or rats
Still very common. Mice get in and eat on wires and hoses.
7. Clogged filters
The first thing we ask a home owner that calls in saying “my spa pool (בריכות ספא) is not heating” is, “Did you clean your filters lately?” That takes care of 90% of those problems.
8. Tripped GFCI breakers
Many things can result in a tripped GFCI breaker. Spa pump, spa pools (בריכות ספא) heater, ozonator and many more
9. Pump seal leaks
Poor water chemistry is almost always the result of a failed pump seal. The symptoms are a small puddle of water around the equipment area
10. Ozonator check valves
The small ozonator check valve fail and as a result water travels into the ozonator and trips the GFCI. Sometimes the ozonator can be dried with a hair drier, and at other times it would have to be replaced.