"CFH" is Call for heat. That means your heater is trying to fire (not an error code). "HL2" is an error code which stands for "High limit #2". This error means the water in the heat exchanger is too hot,and the heater shuts itself down to prevent damage. Most common causes are poor water flow .Make sure the correct pump is running,and you have at least 10psi on the filter gauge. also be sure that the bypass valve is at least 1/2 way closed.The Bypass valve is located on the return line after the filter just passed the first tee.