The display should indicate what the fault is.
If no display fault, check the Fenwal LED.
Maybe low voltage or low gas pressure.
There is a troubleshooting flowchart in the manual that you can follow.
You can review the History to see the last 5 errors.
You can check the status of the Flame Current.
SEQUENCE OF OPERATION
An electronic temperature sensing thermistor in the manifold adapter inlet controls the heater operation.
When the inlet water temperature drops below the temperature set on the operating control, the burner controller supplies power to the combustion air blower through a series of safety interlocks.
The interlocks consist of:
• the pressure switch (PS), which senses that the pump is running,
• the high limit switch (HLS), which opens if the heat exchanger outlet temperature goes above 135° F (57° C), and
• the air flow switch (AFS), which senses the pressure drop across the air metering orifice,
• the automatic gas shut-off (AGS) switch, which opens if the heat exchanger outlet temperature goes above 140° F (60° C).
• the stack flue sensor (SFS), which shuts down the heater if the flue gas temperature reaches 480° F (249° C).
The air flow switch (AFS) senses the pressure drop across the air metering orifice. As soon as there is sufficient air flow, the AFS closes, closing the circuit to the hot surface igniter (HSI), which ignites the fuel mixture.
On a call for heat, the blower and HSI are energized.
In about 20 seconds, the gas valve opens and ignition occurs.
The HSI then switches to a sensing mode and monitors the flame.
