Tankless
How Often Should a Tankless Water Heater Be Flushed?
The short answer
A tankless water heater should be flushed once a year — more often in hard-water areas like Knoxville. Flushing removes mineral scale from the heat exchanger, which is the #1 cause of reduced efficiency and premature failure in tankless units.
Common symptoms
- Tankless unit is 1+ year old and has never been flushed
- Water isn't as hot as it used to be
- Error code on the unit's display
- Reduced hot water flow
- Unit makes unusual noises during operation
Most likely causes
- —Hard water mineral buildup in the heat exchanger
- —Lack of annual maintenance
- —No water softener or treatment
- —Heavy household usage
Safe things you can check
- ✓Check the manufacturer's recommendation — most specify annual flushing.
- ✓If you have hard water (common in Knoxville), annual flushing is essential — scale builds up fast in the narrow heat exchanger channels.
- ✓Flushing uses a descaler (white vinegar or a manufacturer-approved solution) circulated through the unit with a pump.
- ✓This is not a DIY job for most homeowners — it requires the right pump, hoses, and isolation valve kit, and mistakes can damage the unit.
When to call a professional
We flush tankless water heaters with the proper equipment and descaler. Annual flushing protects your investment and keeps the unit heating efficiently — skipping it is the most common cause of premature tankless failure.
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Reviewed by Paul Hall, Owner & Licensed Plumber
The Classic Plumber · Knoxville, TN · License #4268
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