The pressure switch also has a high limit and thermostat in series to disable the heater these 3 components can be replaced using two temperature sensors in a comparison config using software i.e if one sensor is hotter it is a pressure problem if both are hot then an overheat. when both are equal they are compared to the setpoint and heat up the water. A 4 channel relay shield needed for high/low speed of pump,heater and overheat. If more than one pump is used it will require additional relays.