How often should you clean a tankless water heater air filter?
Updated July 2026
Clean a tankless water heater's air-intake filter and its cold-water inlet screen once a year, and the easy way to remember it is to do both when you run the annual descale. These are two different screens with two different jobs: the intake filter keeps dust out of the burner's combustion air, and the inlet screen keeps grit out of the water side. When either clogs, the unit chokes, hot-water flow sags, and the control board starts throwing airflow or ignition error codes. Dusty rooms and homes with shedding pets should halve the interval to every 6 months.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Standard indoor install | Once a year | Fold it into the annual descale visit |
| Garage or dusty mechanical room | Every 6 months | Airborne dust loads the intake screen quickly |
| Home with shedding pets | Every 6 months | Pet hair mats across the intake filter fast |
| Well water or sediment-heavy supply | Inlet screen every 3-6 months | Grit collects on the water inlet screen |
| Unit showing an airflow error code | Clean now | A clogged intake is a common cause and often clears with a rinse |
| Hot water suddenly weak or surging | Check the inlet screen | A restricted inlet starves the flow sensor |
The cost of skipping it
What skipping it costs: a fouled intake or inlet screen shows up as nuisance lockouts, weak or fluctuating hot water, and repeated ignition faults, which usually ends in a service call at $150-300 to clean parts you could have rinsed yourself. The screens are the cheap half of tankless care; the expensive half is scale. Neglect the yearly descale that goes with this cleaning and mineral buildup in the heat exchanger cuts efficiency and can force a $200-600 repair. Do the filters and the descale together and a good unit reaches its 20-year service life.
How to do it (20-30 minutes · DIY, part of annual service)
- Cut power to the unit at the switch or breaker and shut the gas if you are working near the burner.
- Locate the air-intake filter (a small screen at the bottom or behind the front cover), pop it out, and rinse it clean.
- Close the cold-water inlet valve and open a hot tap to relieve pressure on the water side.
- Unscrew the cold-water inlet screen (often inside the inlet fitting), flush out sand and grit, and reseat it.
- Restore water, gas, and power, then run a hot tap for a minute and confirm steady flow with no error code.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing tankless filter cleanings schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
Is cleaning the filter the same as descaling the unit?
No, they are two separate annual tasks that pair well. Cleaning the air filter and inlet screen keeps combustion air and incoming water flowing freely. Descaling circulates vinegar or a descaler through the heat exchanger to dissolve the mineral scale that hard water leaves behind. The filter cleaning takes 20-30 minutes; the descale adds about an hour with a pump and two hoses. Doing both once a year keeps the burner efficient and the flow strong, and many warranties require the descale.
My tankless heater is throwing an error code. Could a clogged filter be the cause?
Often, yes. Many airflow, combustion, and flame-sensing codes trace back to a blocked intake filter starving the burner of air, and low-flow faults can come from a plugged inlet screen. Cleaning both is the right first move before you assume the worst. If the same code returns right after a thorough cleaning, look up that specific code in the manual, since it may point to venting, gas supply, or the flame sensor, which is a technician's call.
Do electric tankless heaters have an air filter too?
No. Electric tankless units do not burn fuel, so there is no combustion-air intake filter to clean, but they do have a cold-water inlet screen that catches sediment and benefits from the same yearly rinse. Gas tankless units have both the air-intake filter and the inlet screen. Either way, the water inlet screen is the piece most likely to explain a sudden drop in hot-water flow, so start there.
Why did my hot-water flow suddenly drop?
The most common culprit on a tankless unit is a partly clogged cold-water inlet screen, which restricts the water reaching the flow sensor and heat exchanger. Scale inside the exchanger does the same thing over time. Clean the inlet screen first, then descale if flow is still weak. If the whole house is affected rather than just the hot side, the issue may be upstream, so check your home water pressure before blaming the heater.