Record the pattern
Save the exact model, warning text or code, and when it appears. Note sanding, cutting, cleanup, seasonal door changes, and any loss of hot-water performance. Take photographs of accessible filter condition and the surrounding workspace without removing service covers.
Check the owner manual's filter procedure. Perform only the care it identifies for owners, with its shutdown, cleaning, drying, and refitting requirements. Do not run the heater without an approved filter, add a denser filter, or wrap the air openings to keep dust out.
Ask for the actual finding
Request inspection of the filter, air path, coil, condensate collection, drain arrangement, and fault history as relevant to the model. Ask whether the finding is a dirty filter, a blocked drain, a sensor issue, or something else. Repeatedly clearing a warning is not a correction.
Have the provider compare the garage use with the manufacturer's allowed environment. Describe solvents, finishes, fuels, and other materials honestly. Dust collection is not a substitute for equipment suitability or applicable fire requirements.
Address the source
Discuss appropriate collection at the woodworking tools and a cleanup plan with a qualified workshop or ventilation professional. Keep that work separate from water-heater service, and coordinate changes that affect the heater's air supply.
If relocation is proposed, compare the new location's electrical, piping, drainage, air, and service access requirements before choosing it. Do not assume another corner solves an environment problem.
Your next step is to send the model, warning, and workshop-use pattern to the heater's service provider. Request a documented fault finding and a practical environment and care plan, rather than replacing parts from the dust coincidence alone.