What is the best solution to flush a tankless water heater?

Tankless water heaters, also known as on-demand or instantaneous water heaters, provide hot water without the use of a storage tank. Instead, they heat water directly as it flows through the unit. This allows tankless heaters to provide a continuous supply of hot water on demand.

Over time, tankless water heaters can accumulate mineral deposits from hard water that will eventually clog the internal components and reduce efficiency. To maintain optimal performance, tankless water heaters need to be flushed regularly to remove these mineral deposits. Determining the best flushing method depends on the specific make and model of your tankless unit.

When to Flush a Tankless Water Heater

Most manufacturers recommend flushing a tankless water heater annually. More frequent flushing may be required in the following situations:

– You have hard water. Areas with high mineral content in the water need more frequent flushing.

– Heavy usage. Homes that use a lot of hot water daily should flush more often.

– Decreased flow rate. If you notice your hot water taking longer to get hot, that’s a sign of mineral buildup.

– Error codes. Many tankless heaters have built-in computer diagnostic systems. Error codes indicating flow restriction are a clue it’s time to flush.

– Older tankless water heater. Mineral scale accumulates over time, so older units need more frequent flushing.

– Installation of a new tankless unit. Flush it before use to remove any manufacturing debris.

Follow your manufacturer’s recommendations to determine the ideal flushing frequency for your specific model in your local water conditions. Many experts suggest flushing twice annually if you have hard water.

How to Flush a Tankless Water Heater

Tankless water heater flushing can be performed using one of the following methods:

Method 1: Isolation Flush

An isolation flush cleans the tankless heat exchanger without sending debris through your home’s pipes. Follow these steps:

1. Turn off power to the tankless unit at the breaker box and turn off incoming water shutoff valves.

2. Disconnect hot and cold water connections. Attach garden hoses to inlet and outlet ports.

3. Connect one hose to inlet port. Place the other into a bucket or drain.

4. Use a pump, like one designed for RV antifreeze, to pump vinegar or descaling solution into the cold inlet.

5. Turn on pump and allow solution to circulate 20-30 minutes.

6. Rinse by pumping clean water through system for 3-5 minutes.

7. Reconnect water lines and turn water supply back on. Turn power back on.

8. Flush indoor faucets until no vinegar smell remains.

Method 2: Whole House Flush

This method sends the descaling solution through the entire plumbing system. Follow these steps:

1. Turn off power to tankless unit at breaker box.

2. Close hot water shutoff valve. Open cold water inlet valve.

3. Connect pump outlet to cold inlet port.

4. Pump vinegar or cleaning solution into the unit, filling water lines throughout home.

5. Circulate solution for 30 minutes. Open hot water faucets one by one to fill all lines.

6. Disconnect pump. Turn cold water shutoff valve off.

7. Open hot water shutoff valve. Turn on hot water faucets and flush until solution is gone.

8. Turn off faucets, turn cold water inlet valve on. Turn power on to tankless unit.

Flush any sediment out of indoor faucets. Avoid using hot water for 30 minutes.

Method 3: Maintenance Flush

For routine flushing, a maintenance flush uses an external hose connection:

1. Locate external hose bib, drain port, or flushing connection on tankless unit.

2. Connect hose and open valve to allow water to flow out of drain.

3. Turn power off at breaker box. Turn cold inlet valve off.

4. Fully open nearest hot water tap. Allow unit to drain.

5. Close hose valve. Disconnect hose. Turn cold water back on.

6. Power unit back on. When tap water runs cold, close tap. Avoid using hot water briefly.

7. Check operation and make sure all valves are fully on.

This quick external flush is useful for routine maintenance of tankless heaters.

Flushing Solution Options

The best solutions for cleaning and descaling a tankless water heater are:

– White vinegar – Mix 1 part vinegar with 4 parts water. An affordable option. Avoid prolonged contact with stainless steel.

– Citric acid – Mix with water per package directions. Biodegradable and compatible with septic systems.

– Phosphoric acid – Sold commercially as tankless unit descaler. Follow package diluting instructions.

– Store bought cleaners – Choose non-toxic formulations made for tankless heaters.

Avoid:

– Hydrochloric acid – Highly corrosive to system components.

– Household bleach

– Lime removers with sulfamic or formic acid

When mixing your own solution, circulate 20-30 minutes before rinsing. Flush with clean water to remove any residual acid.

How to Clean Tankless Water Heater Filters

Many tankless water heaters have an internal sediment filter to trap debris in the water. Over time these can also become clogged with mineral scale. After flushing the tankless unit, inspect and clean the filter:

1. Turn power off to the unit at the breaker box.

2. Turn off water supply valves. Open nearby hot water faucet to depressurize lines.

3. Locate filter. Some twist off while others require unscrewing housing.

4. Remove filter. Rinse debris under running water.

5. Use brush or vinegar soak to remove remaining scale.

6. Reinstall filter. Replace any gaskets or o-rings.

7. Close faucet. Turn on water supply and power.

8. Check for leaks at filter housing. Immediately power off if any are detected.

Replace filters that cannot be cleaned per your owner’s manual. Periodically changing filters can extend the service life of your tankless hot water heater.

Warning Signs It’s Time to Flush

In addition to following the manufacturer’s recommended flushing schedule, look for these signs it’s time to flush your tankless water heater:

Symptom	Cause
Decreased hot water flow rate	Mineral scale buildup in heat exchanger
Hot water takes longer to arrive	Flow restriction from deposit accumulation
Hot water not as hot	Mineral scale reducing heat efficiency
Corrosion visible inside unit	Mineral deposits increasing acidity
Error code display	Computer alerts of flow or ignition issues
Higher energy bills	Scale buildup making unit work harder

Schedule a flush service immediately if you notice any of these signs of clogging. Catching buildup early allows for easier removal compared to letting large amounts of mineral scale accumulate.

Benefits of Flushing a Tankless Water Heater

Regular tankless water heater flushing provides these benefits:

– Restores hot water flow rate

– Helps water heat quickly again

– Removes scale for better heat transfer

– Cleans out internal components

– Reduces risk of overheating and failure

– Improves energy efficiency

– Prolongs lifespan of unit

– Prevents corrosion and mineral buildup

– Allows computer diagnostic system to work properly

– Avoids need for repairs or replacement

Be sure to flush as often as needed based on your water conditions. Annual flushing can help your tankless run optimally for decades.

Professional Flushing Services

While DIY flushing is possible on many units, consider hiring a professional service for:

– High mineral content water that needs frequent flushing

– Lack of time or physical ability to perform maintenance

– Unsure about proper flushing methods

– Difficult access to tankless unit

Look for a licensed plumber or HVAC company that provides professional tankless water heater flushing. Benefits include:

– Experts familiar with all major brands and models

– Proper equipment to isolate, backflush or descale

– Access to commercial descaling solutions

– Able to thoroughly clean entire system

– Evaluate unit function and repairs needed

– Confidence of service done right

Ask in advance about their specific process, solutions used, and any repairs recommended if issues are discovered.

Cost to Professionally Flush a Tankless Heater

Average costs for professional tankless water heater flushing:

– Service call fee – $75 to $150

– Isolation flush – $150 to $350

– Whole house flush – $300 to $600

Actual costs depend on:

– Unit size and complexity

– Extent of mineral buildup

– Any repairs needed

– Local rates for service calls

Ask for an estimate in advance. The initial investment in professional flushing can save money long-term by extending the life and efficiency of your tankless water heater.

How to Maintain a Tankless Water Heater

To maximize performance between flushing, observe these maintenance tips:

– Inspect inlet filter monthly and clean if needed

– Test temperature and flow rate annually

– Check for leaks or corrosion biannually

– Have a professional annual check-up

– Use scale inhibitor if you have hard water

– Follow manufacturer’s flushing recommendations

– Drain off sediment by flushing lines

– Keep the exterior clean

Taking proper care of your tankless unit will ensure it runs efficiently for 20 years or longer. Regular maintenance is key to avoiding scale buildup issues.

Conclusion

Flushing a tankless water heater is vital preventive maintenance to remove accumulated mineral deposits. Allowing internal scale buildup to continue unchecked can lead to loss of heating efficiency, damage from overheating, the need for repairs, and eventual failure.

Consult your owner’s manual to determine optimal flushing frequency. In hard water areas, plan to flush at least annually. Signs like decreased hot water flow signal it’s time for a flush. You can isolation flush just the unit or perform a whole house system flush. Use white vinegar or citric acid solutions to safely dissolve scale.

Regular tankless water heater flushing extends the operating life and provides consistent hot water delivery. Or rely on professional flush services for convenience and peace of mind. With proper care, your tankless hot water heater can provide decades of reliable performance.