HFL,  HL, or  HTR FLOW LOW  Message

Possibly the "Heater Flow is Low" (HFL or HL).

During Heating, For a *High Wattage Heater, there is a 6°F (3.0°C) or greater Difference between  the Sensors, or for a *Low Wattage Heater, there is a 4°F (2.0°C) or greater Difference between the Sensors, indicating a Possible Low Flow Condition.  There may Not be Enough Water Flow through the Heater to carry the Heat Away from the Heating Element.  Heater Start Up will begin again after about 1 Min.  Check for Water Level, Flow Restrictions, Closed Valves, Air Bubbles, and Pump Prime, or Continue for a Detailed Test Procedure.

*Note: For an EL System, a  High Wattage Heater is 4 kW or More, and a  Low Wattage Heater is 2.5 kW or Less.  A 3 kW Heater can be configured as either High Wattage or Low Wattage.  Convertible System is generally configured for High Wattage at 240 Volts or Low Wattage at 120Volts.  A GL or GS System is Always configured as a Low Wattage Heater.