Yes, a tankless water heater needs regular maintenance. Removing the tank did not remove the mineral scale. Most manufacturers ask for descaling at least once a year, and skipping it can cut years off a unit that should run for two decades.
We inspect homes across Northeast Texas, Southwest Arkansas, and Southeast Oklahoma, and a neglected tankless unit looks identical to a maintained one from the outside.
Here is what the maintenance involves, what it costs, and what an inspection can tell you about a unit with no service history.
What Kind of Maintenance Does a Tankless Water Heater Need?
Four things: descaling the heat exchanger, cleaning the inlet water filter, checking the air intake and venting, and inspecting the condensate drain. Descaling is the big one.
Descaling the Heat Exchanger
Every gallon through the heat exchanger leaves behind a little calcium and magnesium. That limescale insulates the coil so the burner works harder, and narrows the passage so flow drops. Descaling circulates a mild acid to dissolve it, which requires isolation valves (also called service valves) on the hot and cold lines.
What we look for: whether those valves exist at all. Plenty of units in our area were installed without them, which means the unit has never been descaled and cannot be until a plumber adds them. It is one of our most common tankless findings.
Cleaning the Inlet Water Filter
A small screen where cold water enters catches grit and pipe scale. When it clogs, flow drops and the unit may short-cycle or throw a code. Rinse it every time you descale, more often on a well.
What we look for: filter housings that have never been opened, and sediment consistent with untreated well water.
Checking the Air Intake and Venting
Gas units need clean air in and exhaust out. A blocked intake or damaged vent termination can push combustion gases back into the home, so this one is about safety, not efficiency.
What we look for: improper vent material, inadequate clearance at the termination, missing combustion air, and vent runs modified after installation. Venting defects are the findings we treat most seriously on any gas appliance.
Inspecting the Condensate Drain
Condensing units produce acidic water that drains through a trap, often through a neutralizer cartridge. Check that the line is clear and the media is not used up.
What we look for: condensate draining to an improper location, missing neutralizers, and corrosion staining showing acidic water has run where it should not.
How Often Should You Flush a Tankless Water Heater?
Once a year is the baseline. Harder water means more often. The USGS classifies water hardness in four bands, and your band drives your schedule:
| Water hardness | mg/L as CaCO₃ | Grains per gallon | Descale every |
|---|---|---|---|
| Soft | 0–60 | 0–3.5 | 12–18 months |
| Moderately hard | 61–120 | 3.5–7 | 12 months |
| Hard | 121–180 | 7–10.5 | 6–9 months |
| Very hard | 180+ | 10.5+ | 6 months |
Hardness bands are the USGS classification. Intervals are general guidance; defer to your manual.
Municipal supply in the Texarkana area generally falls in the moderately hard range, so an annual descale is usually right. Private wells vary a lot and often run harder, which matters for anyone buying rural property.
A well inspection can tell you a great deal about your home’s water quality, including the hardness that sets your schedule.
Warning Signs Your Unit Needs Service Now
These are also the symptoms we ask sellers about during an inspection:
- Hot water that fluctuates: Temperature swinging mid-shower is the classic scale symptom.
- Reduced flow or a longer wait: For hot water, especially with two fixtures running.
- Error codes: Many point straight at flow problems tied to maintenance.
- Water pooling near the unit: Could be the condensate line, could be worse.
What Happens If You Skip Maintenance?
The unit gets less efficient, then it stops holding temperature, then it dies early. The consequence that catches people off guard is the warranty. Navien states that failing to perform the maintenance in the user manual may void its limited warranty.
If your exchanger fails in year eight and you cannot show service records, that repair is yours. This is why we tell buyers to ask for service documentation before closing, not after.
According to ENERGY STAR, life expectancy for demand water heaters runs about 20 years and a qualified gas model saves a family of four roughly $95 a year. Both figures assume maintenance. Neglected units can fail a decade early.
Tankless vs. Traditional: How Maintenance Differs
Both need yearly attention, but the work is different. A tank heater gets drained to flush sediment off the bottom, and it has an anode rod that wears out and needs replacing. A tankless unit has neither. The scale that would settle harmlessly at the bottom of a tank lands on the heat exchanger instead, which is the expensive part.
| Factor | Traditional tank | Tankless |
|---|---|---|
| Yearly task | Drain and flush sediment | Descale the heat exchanger |
| Hardware needed | A garden hose | Isolation valves and a pump |
| Also check | Anode rod, T&P valve | Inlet filter, venting, condensate |
| Typical lifespan | 8 to 12 years | Up to 20 years |
Most homes in our service area still have tank units, with tankless showing up mostly in newer builds and remodels. Buyers tend to assume tankless means less upkeep.
Can You Flush a Tankless Water Heater Yourself?
Many homeowners can, if the unit has isolation valves and you are comfortable around gas appliances and shutoffs. You will need a utility pump, two hoses, and a five-gallon bucket.
Check your manual on solution first: Rinnai specifies undiluted white vinegar and prohibits chemical descalers outright, Noritz specifies distilled food-grade vinegar, and other brands permit a commercial descaler.
The brands genuinely disagree, and using a prohibited solution can void the warranty. If the valves are missing or the unit is throwing codes you cannot identify, hire a plumber.
What a Home Inspection Tells You About a Tankless Water Heater
A home inspection tells you the condition and installation quality of the unit you are about to inherit, which is the one thing no maintenance guide can answer. When you buy a home, you get the water heater and its whole service history, including the parts nobody wrote down.
On a tankless unit, we report:
- Whether isolation valves are present, meaning whether the unit can be serviced at all
- Whether venting, vent material, and combustion air are correct
- Whether the condensate drain and neutralizer function and drain properly
- Visible corrosion, leakage, or staining around connections
- Whether the unit responds and holds temperature during testing
- Installation defects: clearances, mounting, gas supply, and wall support
Scope matters here, because it is what makes the report trustworthy. A home inspection is a visual, non-invasive assessment. We do not descale the unit, measure scale inside the exchanger, or certify how many years it has left, and no inspector can. What you get is an accurate account of what is there and what needs attention, before you own it.
Inspection Gator has been family owned and operated since 2008, with 10,000+ inspections completed and licensing in Texas (TREC 10108), Arkansas (HI1529), and Oklahoma (OK70002339).
The water heater is one item on a list that runs from roof to septic, alongside the components that need the most routine maintenance elsewhere in the house.
Related Questions to Explore
Does a tankless hot water heater need maintenance?
Yes. People hear “no tank” and assume “no upkeep,” but the tank was never the part that needed servicing. Scale forms on the heat exchanger regardless, and on a tankless unit that exchanger is the expensive component.
What happens if a tankless water heater is never flushed?
Scale builds until the unit cannot maintain output. Temperature swings and reduced flow come first, then error codes, then failure of the exchanger itself. On hard water, that can happen inside five years.
How can I tell if a home’s tankless water heater has been maintained?
Ask the seller for service records, and check whether isolation valves are installed. No valves is strong evidence the unit has never been descaled. Beyond that, you need eyes on the installation, which is what the water heater portion of a home inspection covers.
Do you still need maintenance with a water softener?
Yes, though less often. A softener slows scale and many owners stretch to 18 months between descalings, but the inlet filter, air intake, venting, and condensate drain still need checking. Water quality drives a lot of what goes right or wrong in a home, which is also why we look closely at what a sewer scope inspection can reveal.
When to Call a Professional
Call a plumber for the service work. descaling a unit with no isolation valves, clearing codes you cannot identify, or anything involving gas supply or venting. A plumber services the unit you own.
Call us for questions or a trained eye. An inspection tells you the condition of a unit you are about to buy, before the money moves and while findings can still affect the deal.
Those are two different jobs, and buyers regularly discover the second one too late.
Conclusion
- Descale once a year, more often on hard water or well water. Check your hardness, do not guess.
- Isolation valves are not optional. No valves means the unit has never been descaled and cannot be until they are added.
- If you are buying, get it in writing. Service records from the seller, and an inspection report on condition and installation.
Buying a home with a tankless water heater, or want a straight answer about a system you inherited?
Schedule your home inspection with Inspection Gator and find out what condition it is really in, in writing, within 24 hours.
