Tankless water heaters need annual descaling, a filter screen cleaning, and a combustion and venting check. That is more attention than a tank heater requires, and skipping it is the single most common reason tankless units fail early in the Hill Country.
Descaling: The One That Matters Most
Inside a tankless water heater is a heat exchanger with narrow passages that water moves through while being heated very rapidly. Those two conditions — tight passages and a high temperature differential — make it the ideal place for mineral scale to form.
Descaling circulates a food-grade descaling solution through the heat exchanger for a period of time, dissolving accumulated calcium and magnesium. The unit comes back to full efficiency, and more importantly the exchanger stops overheating in the scaled areas.
Once a year is the standard interval. In hard water without treatment, twice a year is more realistic. If you skip it entirely, expect declining performance within two years and a failed exchanger well short of the unit’s rated twenty-year life — a repair expensive enough that homeowners often replace the whole unit instead.
The Inlet Filter Screen
Every tankless unit has a small screen on the cold water inlet that catches sediment and debris before it reaches the exchanger. It clogs, and when it does, flow drops.
The symptom is confusing: reduced hot water pressure, or the unit failing to fire because flow has fallen below its minimum activation threshold. Homeowners often assume the heater is failing when a two-minute screen cleaning would fix it.
Combustion, Venting, and Condensate
Gas tankless units burn fuel at a high rate, and that side of the system needs attention too.
We check burner condition and flame quality, inspect the venting for obstruction and secure connections, and verify the unit is drawing adequate combustion air. On condensing models — which extract additional heat from exhaust gases — there is a condensate drain that can clog, and a neutralizer cartridge that has to be replaced periodically because the condensate is acidic.
A blocked condensate line will shut a condensing unit down, and it is a routine finding on heaters that have gone several years without service.
What Homeowners Can Do
A few things are genuinely DIY. Keep the area around the unit clear so it can breathe. Check the vent termination outside for nests, debris, or blockage, especially after a storm. Note any error codes rather than just power-cycling past them — the code is diagnostic information, and clearing it without addressing the cause hides a developing problem.
Descaling kits are sold to homeowners, and some people do it themselves successfully. It requires isolation valves — which is why we install service valves on every tankless unit we put in, whether or not the homeowner intends to use them. If your unit lacks them, descaling requires cutting into the lines, which is why it gets skipped.
Treating the Water Is Cheaper Than Descaling It
The most effective maintenance is preventing scale rather than removing it.
A water softener upstream of the heater removes the calcium and magnesium before they ever reach the exchanger. Homes with softened water often need descaling far less frequently, and the unit holds its efficiency for its full service life.
If a full softener is not practical, a scale-inhibiting filter is a middle option. Understanding what is actually in your supply starts with a water quality test, and homeowners dealing with sediment as well as hardness sometimes need a whole house water filter alongside softening.
Warranty Depends on It
Worth knowing: most tankless manufacturers require documented annual maintenance to keep the warranty valid. These units carry long warranties — often fifteen years on the heat exchanger — but a claim on a scaled exchanger with no service records is routinely denied.
Scheduled water heater maintenance produces that documentation. Members of our Care Club maintenance plan get it on schedule without having to remember, which is the practical reason most tankless owners join.
If your unit is already showing symptoms — inconsistent temperature, error codes, reduced flow — that is a repair conversation rather than a maintenance one.
We service tankless systems across Fredericksburg, Kerrville, Boerne, Comfort, and the surrounding Hill Country. To schedule descaling, contact 72 Degrees or call (830) 468-5316.
