A rumble during a heating cycle can occur when water moves through sediment near the bottom of a tank. Other equipment or piping can make a similar sound. The timing gives a technician a place to start.
Listen for when it begins
Note whether the sound starts during recovery after a shower or when you first open a tap. Report whether hot water capacity changed or whether you see moisture near the heater. Leave covers closed and keep clear of hot piping.
Ask what the technician found
Share the model and any record of prior flushing. The technician can assess the tank and explain whether maintenance fits its condition. If they recommend repair or replacement, ask what finding supports that choice.
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