I have an older hot tub (Great Lakes Spas Performer Series II, also says Hercules model #PGL06HB03) The heater will only run when the jets are running. When the timer clicks over to turn on the heater on the light comes on for a second then shuts right back off. Any help diagnosing this problem would be greatly appreciated.
Thanks,
Dave

is it a 2 spd pump - does low speed run for the heat demand mode - if not, is the pump motor humming - possible blown capacitor or motor problem

Okay... 2 speed pumps are commonly used for hot tub operation. YOu want to be sure that your low speed pump is coming on with the time clock. you can rotate the dial clockwise to force it on... naturally you'll want the high speed pump off at this time. If the low speed comes on and you can verify operation and flow by visually inspecting the water coming out of the jets then you may have a pressure switch problem. the pressure switch is there to tell the heater that there is water flow and its okay to fire. Sometimes pressure switches come out of adjustment and wont let the heater come on on low speed.. but may allow the heater to fire on high speed. This can be caused by a dirty filter... so if you havent cleaned it lately .. might wanna.