I am having a problem with my spa bubbler. There is an air-operated plunger switch near the spa that cycles the bubbler through its operation. There is an air line that runs from the plunger switch to the pool timer control. The plunger switch has stopped functioning - I can press it multiple times and nothing happens. The bubbler is stuck on and won’t turn off. I had to force it to turn off by turning off the breaker. What’s the best way to troubleshoot this problem?