Flow, temperature, displayed codes, maintenance records, and energy type all shape the conversation.
The short answer
Record which fixtures are affected and whether the unit fails to start, changes temperature, stops under simultaneous use, or displays a code. Do not open the cabinet, alter fuel or venting, or repeatedly reset the appliance. Use the exact manufacturer instructions for the model.
What to notice
Describe demand precisely
Note which outlets were running when the symptom appeared and their approximate order of use. A low-flow fixture, mixing issue, demand beyond unit conditions, scale, control fault, supply issue, or energy problem can produce different patterns. A provider needs actual operating details rather than the phrase “not keeping up.”
Bring the service history
Find the model, installation paperwork, maintenance dates, previous codes, and any filter or treatment records. Do not claim maintenance was completed if there is no record. Water quality and manufacturer requirements vary. Ask what inspection supports a cleaning, component repair, or replacement recommendation.
Respect venting and fuel boundaries
Visible vent condition, exhaust odor, gas odor, unusual combustion sound, or repeated shutdown changes the safety response. Leave the area and contact the appropriate emergency or utility service for a suspected fuel emergency. Confirm that anyone working on gas fitting has the required Massachusetts credentials for that scope.
One useful question
Does an error code name the part to replace?
Not always. A code points to a condition defined by that manufacturer and model. Supporting checks may be required before a part is condemned. Record the code accurately and ask the qualified servicer to explain the test and repair basis.