A tankless water heater maintenance schedule is short enough to fit on an index card, and following it is the difference between a 20 year appliance and a 7 year one. This checklist lays out every task by interval, what each takes, and the one piece of paperwork worth keeping.
The master schedule
| Interval | Task | Time | Who |
|---|---|---|---|
| Annually (adjust for hardness) | Descale/flush the heat exchanger | 45 to 90 min | You |
| Annually, with the flush | Clean the cold water inlet filter | 5 min | You |
| Annually | Clean or check the air intake filter (gas models with one) | 5 min | You |
| Twice a year | Visual check of intake and exhaust terminations | 5 min | You |
| Ongoing (condensing units) | Confirm condensate drain flows and neutralizer media is live | 5 min | You |
| Every 2 to 3 years | Professional combustion and gas pressure check | Service visit | Technician |
| Every flush | Date and log it | 30 seconds | You |
The flush: the item that carries the schedule
Everything else on this list is hygiene; the flush is the task that determines the unit’s lifespan, because scale in the heat exchanger is the dominant tankless killer, per HARD WATER AND SCALE. The interval is set by your water, not the calendar’s roundness: annual under 7 grains per gallon, every 6 to 9 months at 7 to 12, every 4 to 6 months above that, with the reasoning at HOW OFTEN SHOULD YOU FLUSH and hardness testing covered here.
The job itself is a pump, two hoses, a bucket, and a flushing agent circulated through the service valves, walked through step by step at DESCALING A TANKLESS WATER HEATER. Agent choice, vinegar versus formulated descaler, is a hardness decision covered in the comparison; packaged kits from suppliers such as Chromex bundle the hardware and solution so the annual job needs no shopping trip. And if your unit lacks the isolation valves that make flushing possible, having them added is item zero on this whole schedule.
The five-minute items
Inlet filter screen. A small strainer where cold water enters, it catches pipe grit before the exchanger does. Shut the cold isolation valve, unscrew the filter plug, rinse the screen, reinstall. Do it every flush; a clogging screen mimics scale symptoms convincingly.
Air intake filter. Many gas units filter combustion air, and a linty filter is behind a surprising share of combustion error codes. Slide out, rinse or vacuum, dry, reinstall.
Vent terminations. Twice a year, eyeball where the intake and exhaust exit the building: nests, leaves, lint mats, snow. Blocked venting shuts units down and, worse, degrades combustion.
Condensate path (condensing models). High-efficiency units produce acidic condensate that must drain freely, usually through a neutralizer cartridge. Confirm the drain drips during operation and replace neutralizer media when consumed, because a blocked condensate line stops the unit and an exhausted neutralizer quietly eats whatever drain it empties into.
The professional visit
Every 2 to 3 years, a technician with a combustion analyzer earns their fee: verifying gas pressure, inspecting the burner and flame rod, and confirming the unit combusts as designed. This is also the visit that keeps gas-side work off your plate entirely, which is where DIY should stop anyway.
The paperwork habit
Most tankless heat exchanger warranties condition coverage on maintenance, and scale damage is the excluded cause manufacturers look for first. A dated log line per flush, plus receipts for solution or service, is the entire burden, and it is the difference between a covered exchanger and an argument, detailed in WATER HEATER WARRANTIES. Tie the schedule to something you already remember: daylight saving weekend, the furnace filter, the smoke alarm batteries.
The bottom line
One real job on a hardness-based clock, three five-minute checks, a technician every few years, and a log line each time. That is the entire ownership manual for a machine that will repay the discipline with two decades of hot water.