kcc_96Jetsetter

Hello, First time poster and newbie to spas. I inherited a 96 hot springs jetsetter with the purchase of my house. Physically appears to be in shape but it will not heat. So far I have replaced the circulation pump, removed the heater to check for obstructions, and replaced some of the pvc hose that appeared brittle. The pump is running fine but the spa is not heating. Before I call a tech out to the house ($115 service call) does anyone have some ideas i could try? I'm fairly handy and have an have tools to do most jobs. Thank you in advance for your constructive advice.