Fixing an E1 error code on a gas tankless water heater requires addressing ignition and flame detection failures systematically. Prerequisite: Turn off power and gas supply before inspecting internal components. First, check that the main gas supply valve is fully open. Remove the front cover and locate the flame sensor rod; gently clean any carbon soot or oxidation off its metal surface using fine-grit sandpaper. Next, inspect the igniter electrodes for hairline cracks or debris. Finally, power cycle the unit to clear control board memory. Verification: Test hot water taps and verify through the viewing window that burners ignite stably without triggering an E1 fault.
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