Tankless Water Heater Maintenance Cost

Minerals in hard water build up inside a tankless water heater's heat exchanger. Descaling (also called flushing) removes that scale. Angi puts a professional descaling at $150 to $350; Modernize lists $150 to $400.

Maintenance prices

What a descaling involves

HomeGuide describes the process: the unit is drained, a solution of 50% white vinegar and 50% water is run through it, and it is then flushed with clean water. A technician may also clean the inlet filter and check the venting and burner.

Doing it yourself

Angi lists DIY-friendly parts at about $20 to $100 and recommends a professional for anything beyond simple cleaning or filter changes. Units under warranty may require proof of maintenance, so check the manufacturer's terms before skipping the service visit.

Why maintenance pays off

Repairing scale-related damage costs far more than descaling. Angi lists heat exchanger repairs at $500 to $1,300 and sensor repairs at $150 to $400. HomeGuide gives tankless units a lifespan of 15 to 20 years. More on repairs: tankless water heater repair cost.

Tank water heaters

Tank units need flushing too, to clear sediment from the bottom of the tank. See water heater maintenance cost.

Why tankless heaters need maintenance

As water passes through the heat exchanger, minerals such as calcium and magnesium can build up inside it. Scale reduces efficiency, restricts flow, and can trigger error codes or damage the unit. Most manufacturers recommend periodic flushing, and some warranties require it.

What a maintenance visit includes

• Flushing the heat exchanger with a descaling solution, pumped through isolation valves.
• Cleaning the inlet water filter screen.
• Checking the burner, igniter and flame sensor on gas units.
• Inspecting venting and the condensate line on condensing models.
• Checking for error codes and testing operation.

How often to service

The right interval depends on water hardness and how much hot water the household uses. Homes with hard water need flushing more often. Your installer or the manufacturer's manual can recommend a schedule.

More on doing it yourself

If your unit has isolation valves, flushing is a manageable DIY job with a small pump, hoses and a descaling solution. Without service valves, a plumber may need to add them first, which is a one-time cost that makes every future flush easier.

Ways to reduce scale

1. Install a water softener or scale-reduction system ahead of the heater.
2. Keep the temperature setting moderate; higher temperatures speed up scaling.
3. Follow a regular flushing schedule.

In Texas

Hard water is common in many Texas cities, including San Antonio and Austin, so tankless heaters in these areas typically need more frequent flushing than in soft-water regions.

Signs your unit needs descaling now

Scale builds up gradually, and the heater usually gives warnings before it shuts down:

• Hot water that swings between hot and lukewarm during a shower.
• Lower hot water flow than before, especially when two fixtures run at once.
• An error code on the display related to scale, overheating or flow.
• A unit that is noisier than it used to be.

Many newer models count operating hours and show a maintenance reminder. If you see any of these signs, schedule a flush before the unit starts shutting off.

Hard water and service intervals

How often a tankless unit needs flushing depends mainly on the hardness of your water and how much hot water your household uses. In soft water, once a year or less may be enough. In hard water areas, the manufacturer may recommend more frequent service, and some plumbers suggest installing a scale-reducing filter on the cold water line to the heater. Your local water utility publishes hardness figures in its annual water quality report, which is a useful starting point.

Gas units have extra checks

A gas tankless heater has a burner, a fan and a vent system in addition to the heat exchanger. During a full service, a technician can clean the burner and the air intake filter, check the flame sensor and ignition, inspect the vent for blockages or loose joints and confirm the condensate drain on condensing models is clear. Electric units have fewer parts to check, so their service is usually quicker.

Keeping the warranty valid

Most tankless warranties require the heater to be installed and maintained according to the manual. Scale damage is often excluded if the unit was never descaled, which can turn an expensive heat exchanger failure into an out-of-pocket repair. Keep receipts for each service, or note the dates if you do it yourself.

What a DIY flush needs

If your unit has isolation valves, a basic flush takes a submersible pump, two hoses, a bucket and a descaling solution or white vinegar. The power or gas is turned off, the valves are closed, and the solution is circulated through the heat exchanger for the time the manual recommends. Then the system is rinsed with fresh water, the inlet filter screen is cleaned, and the valves are reopened. Follow the manual's steps exactly. They differ between models.

Maintenance plans

Some plumbing companies offer yearly maintenance plans that include a tankless flush, priority scheduling and discounts on repairs. A plan can make sense if you would otherwise pay for a service call every year anyway. Compare the plan price with the cost of a single flush, and check what is actually included. Some plans cover only an inspection, not the descaling itself. Also ask whether the plan transfers to a new owner if you sell the house, since that can be a small selling point.

Cost of skipping maintenance

Scale does not just lower performance. It makes the heat exchanger run hotter, which can trigger safety shutdowns and shorten the life of the unit. A flush costs far less than a heat exchanger or a new heater, and it is the single most effective thing you can do to protect a tankless unit.

Sources

1. Angi: How Much Does It Cost to Repair a Tankless Water Heater? (updated Oct 10, 2026)
2. HomeGuide: How Much Does Water Heater Repair Cost? (Aug 7, 2025)
3. HomeGuide: How Much Does a Tankless Water Heater Cost? (Jan 2, 2026)
4. Modernize: Water Heater Repair Cost 2026