Hm-mh. I overlooked something important. Timers are not commonly used on pools in much of the Southeast, and I forget things that I haven't often had to deal with.

Anyhow, heater's have thermal safety's that SHOULD shut the heater off, if the pump is off. But it's not good to depend on that.

If your Jandy unit does not automatically turn off the pump BEFORE turning the heater off, you'll need to put a flow switch in series with the Jandy control unit, so if flow is low, the heater cannot fire.