Tankless water heater repair costs $300 to $700 in 2026
Most tankless water heater repairs run $300 to $700. A descaling flush, which fixes the most common problem, is $150 to $300. Igniters, sensors and thermistors are $150 to $450. A heat exchanger is the big one at $500 to $1,300, and at that price on an old unit, replacement ($1,500 to $4,000) starts to make sense.
Cost by job
| Diagnosis and error code check | $75 to $250 |
|---|---|
| Descaling flush | $150 to $300 |
| Igniter or flame rod | $150 to $350 |
| Flow sensor | $150 to $400 |
| Thermistor or thermostat | $200 to $450 |
| Water valve or inlet filter | $150 to $350 |
| Control board | $300 to $700 |
| Venting or exhaust repair | $200 to $600 |
| Heat exchanger | $500 to $1,300 |
| Gas valve | $350 to $800 |
What to know before you book
| Scale is the usual cause | Most tankless calls trace back to mineral scale in the heat exchanger. Rinnai, Navien and Rheem all tell owners to flush yearly, and in hard water areas they mean it. A $150 to $300 flush prevents a $1,000 heat exchanger. |
|---|---|
| Your warranty may be void | Manufacturers can deny a heat exchanger claim if the unit was never flushed or was installed without a permit. Keep the flush receipts. |
| Read the error code | Tankless units show a code on the panel. E11 or 11 on a Rinnai is ignition failure; LC is scale; 12 is flame loss. Look it up before you call so you know whether it is a $200 fix or a $1,000 one. |
| Fewer techs know them | Not every plumber services tankless. The brand's website lists trained installers. An untrained plumber charges the same and guesses. |
| Repair or replace | Replace if the repair is over half the price of a new unit, or the unit is past 15 years. Tankless heaters last 20 years with flushing and 10 without. |
| Emergency | No hot water is not a night time emergency for most homes. Wait for the morning rate; the after hours fee is $100 to $350. |
Why it costs what it costs
A tankless heater is a small furnace with sensors, a control board and a heat exchanger the size of a shoebox. The parts cost more than tank heater parts, fewer plumbers carry them on the truck, and a lot of the labor is diagnosis. That is why a tankless repair averages $600 while a tank repair averages $400, and why the flush that keeps the exchanger clean is the best money you will spend on it.
What will this cost me?
Pick the job, your state's cost level and when you need it. The estimate updates as you change them.
Estimates from published 2026 cost guides. Get a written quote before work starts.
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Book a free 15 minute callNo pitch deck. We run your audit live on the call.Common questions
How much does it cost to repair a tankless water heater?
$300 to $700 for most repairs in 2026. A flush is $150 to $300; a heat exchanger is $500 to $1,300.
How often should a tankless water heater be flushed?
Once a year, or twice a year in hard water areas. It is the repair that prevents the others.
Should I repair or replace my tankless water heater?
Repair unless the quote is over half the price of a new unit or the heater is more than 15 years old.
Why is my tankless water heater showing an error code?
Codes point to ignition, flame loss, scale, or a sensor. Look up the code for your brand before calling; it tells you what the repair will roughly cost.
Does a plumber or an HVAC tech fix a tankless heater?
A plumber, ideally one trained by the brand. The gas and venting side overlaps with HVAC, but plumbers do most of the work.