Record the warning precisely
Save the full model, exact message or code, and when it appears. Note whether hot-water performance changes and whether the warning returns immediately or after several days. A photograph of the display is more useful than remembering that it said something about a filter.
Describe changes in garage doors, storage, dust-producing work, room use, or equipment operation. Include any new object near the heater's air openings. These are investigation clues, not a remote diagnosis.
Use the owner care procedure once correctly
If your manual assigns filter cleaning to the owner, follow that procedure and its refitting requirements. Do not open internal compartments, alter sensors, add filter layers, or use a borrowed reset sequence. If you cannot confirm the correct owner procedure, ask the service provider for it.
Tell the technician what was done and how quickly the warning returned. A fault that keeps returning deserves a finding even if hot water is still available.
Ask what the technician measured
Request a check of the filter fit, air path, relevant fan operation, and sensor readings as required for this model. Ask whether the observed conditions match the warning's actual trigger. A summer coincidence should not lead straight to replacing a sensor or blaming the homeowner's cleaning.
If the installation environment is contributing, request a correction that preserves the manufacturer's air and service requirements. Have related building or ventilation work assigned to the appropriate qualified provider.
Your next step is to send the model, warning photo, cleaning history, and seasonal observations to a provider familiar with that heater. Ask for the cause, supporting findings, and a correction plan rather than another reset alone.