E5 error and no ignition, repeated clicking from igniter on gas model

Safety first: Turn gas OFF at the shutoff valve and set the gas control to OFF. Disconnect power and allow the burner compartment to cool.

• Access igniter: Remove the burner access door on the Giant gas heater. Locate the igniter assembly (hot surface or spark type) near the main burner.
• Inspect igniter: Look for cracks in the ceramic, broken tip, or heavy deposits. A damaged igniter must be replaced.
• Check wiring and connector: Ensure the igniter harness is firmly connected to the control board and not pinched or burned.
• Verify igniter position: The igniter tip should be in the gas stream as specified by Giant (typically a few millimeters from the burner port). Adjust mounting if it has shifted.
• Test operation: Restore power and gas, then call for heat. Observe through the sight glass: if no glow (hot surface) or no spark (spark igniter), replace the Giant igniter assembly. If a good igniter still does not light gas, the control board or gas valve may be faulty and should be diagnosed by a technician.