Water temperature.

It does not work off temp. it works off a timer that you set. You can set multiple on off times, but when its on, it on non stop until you set the timer to off. So I set mine when we get up for on, then when we leave to off, the back on at lunch, then off after lunch, then on at 5 then off at 11.

The documentation that came with the unit does not say....the max allowable temperature for the valve and the pump to work is 150 degrees. I think the valve closes at 120.