The short answer is: you should have your tankless water heater flushed at least once per year. Most manufacturers and plumbing professionals recommend an annual flush to remove mineral scale buildup that accumulates inside the heat exchanger. The primary keyword is how often should i have my tankless water heater flushed, and for most US households, once every 12 months is the baseline — though homes with hard water (above 7 grains per gallon) may need service every six months. Skipping this maintenance can reduce efficiency by up to 30% and shorten the unit’s lifespan, according to the U.S. Department of Energy.
Why Flushing Matters for Your Tankless Water Heater
Unlike traditional tank water heaters, tankless models heat water on demand using a high-efficiency heat exchanger. Over time, dissolved minerals — especially calcium and magnesium — precipitate out of hot water and form scale inside the exchanger. This scale acts as an insulator, forcing the unit to work harder and use more energy. The Energy.gov water heating guide notes that even 1/8 inch of scale can reduce heat transfer efficiency by 20–40%. Flushing uses a food-grade descaler (typically white vinegar or a citric acid solution) to dissolve that buildup and restore performance.
What Happens If You Don’t Flush?
- Reduced hot water output: Scale restricts flow, so you may get lukewarm water or fluctuating temperatures.
- Higher energy bills: The heater runs longer to compensate for lost heat transfer.
- Error codes and shutdowns: Many modern units display fault codes when flow is too low due to scale.
- Premature failure: A clogged heat exchanger can crack or leak, requiring costly replacement.
How Often Should You Flush? A Detailed Schedule
The exact frequency depends on your water hardness, usage volume, and the manufacturer’s recommendations. The International Association of Plumbing and Mechanical Officials (IAPMO) emphasizes that local water conditions are the primary factor. Below is a practical schedule based on typical US conditions.
| Water Hardness Level | Recommended Flush Frequency | Notes |
|---|---|---|
| Soft (0–3 grains per gallon) | Every 12–18 months | Low mineral content; annual flush is still wise for warranty compliance. |
| Moderate (3–7 grains per gallon) | Every 12 months | Standard recommendation for most US municipal water supplies. |
| Hard (7–10 grains per gallon) | Every 6 months | Common in the Midwest and Southwest; scale forms faster. |
| Very hard (10+ grains per gallon) | Every 3–4 months | Consider a water softener to reduce flushing frequency. |
Signs Your Tankless Water Heater Needs Flushing Sooner
Even if you follow a schedule, watch for these warning signs that indicate buildup is already affecting performance:
- Rising gas or electric bills with no change in usage.
- Water temperature fluctuations — hot water turns cold mid-shower.
- Reduced flow rate from faucets or showerheads.
- Error code on the display (e.g., “11” or “12” on many brands, indicating low flow or overheating).
- Rumbling or sputtering sounds from the unit during operation.
If you notice any of these, schedule a flush immediately. For comprehensive maintenance, consider our water heater repair services.
DIY vs. Professional Flushing: What’s Right for You?
DIY Flushing Basics
Some homeowners flush their own units using a submersible pump, two hoses, a bucket, and white vinegar. The process involves isolating the unit, circulating the descaling solution for 45–60 minutes, then rinsing with fresh water. While DIY can save money, it carries risks:
- Improper valve sequencing can damage the unit.
- Incomplete rinsing leaves acidic residue that can corrode internal parts.
- You may miss other issues like sediment in the inlet filter or worn gaskets.
Professional Service Benefits
A licensed plumber brings specialized equipment (e.g., a flow meter, commercial-grade descaler, and a flush kit) and can inspect for leaks, check the pressure relief valve, and test the thermistors. Typical cost for professional flushing in the US ranges from $150 to $350, depending on your region and the unit’s accessibility. This is a small investment compared to a new heat exchanger, which can cost $800–$1,500. Our drain cleaning and leak detection teams also ensure your entire plumbing system stays in top shape.
How Flushing Extends the Life of Your Unit
Most tankless water heaters are designed to last 20 years or more — but only with proper maintenance. Annual flushing prevents the #1 cause of failure: scale-induced overheating. The EPA WaterSense program encourages water-efficient practices, and a well-maintained tankless heater is inherently more efficient than a tank model. By flushing annually, you protect your investment and keep energy costs low.
Frequently Asked Questions
Can I flush my tankless water heater myself?
Yes, if you have basic plumbing skills and the manufacturer’s flush kit. However, mistakes can void your warranty or cause leaks. Most manufacturers recommend professional service for the first flush to ensure proper technique.
How long does a tankless water heater flush take?
A professional flush typically takes 1–2 hours, including setup, descaling circulation, rinsing, and system testing. DIY flushes may take longer if you’re learning the process.
What happens if I never flush my tankless water heater?
Scale buildup will gradually reduce efficiency, raise energy bills, and eventually cause the heat exchanger to overheat and crack. Many units will display error codes and shut down, leaving you without hot water until repairs are made.
Does a water softener eliminate the need for flushing?
No. A water softener reduces hardness minerals but does not remove all particles. Annual flushing is still recommended to clear any residual sediment and maintain warranty coverage.
Is flushing covered under warranty?
Most manufacturers require proof of annual flushing to honor the warranty. If you skip it, a scale-related failure may not be covered. Keep receipts or service records.
Can I use vinegar instead of a commercial descaler?
White vinegar is effective for light to moderate scale and is safe for most units. For heavy buildup, a citric acid-based commercial descaler may work faster. Always follow the manufacturer’s guidelines.
Don’t wait until your tankless water heater starts acting up. Schedule a professional flush today to keep your system running efficiently and avoid costly emergency repairs. Contact MyTownPlumber for expert service — we also handle pipe repair, sump pump installation, toilet repair, sewer line repair, and water softener solutions. Click here for a special plumbing offer.