if you switch the heater on via the aqualink and the Heater LED remains on Green on the One Touch panel or doesn't come on on the pcb (LED under "Heater"), then check 1: water temp readout, 2: thermostat setting is higher than water temp, 3: the water is flowing in circuit. If the heater LED turns RED but the heater does not fire, connect the 2 heater wires together (pins 1 & 2 green terminal bar). if the heater does not fire, the problem is with the heater or wires.