The short version: Tankless water heaters need one major annual service (descaling/flushing) and two 30-second checks every 6 months (air filter + condensate trap). Properly maintained, they last 20+ years. Neglected, they fail in 8-10. In Montgomery County's moderately hard water, skipping descaling is the #1 reason we see premature failures.
Why maintenance matters more in Maryland
Tankless water heaters work by running all your home's hot water through a heat exchanger — a stainless steel or copper coil directly above a gas flame. Every gallon of water leaves trace minerals behind. Over time those minerals build up as scale inside the coil, restricting flow, reducing efficiency, and eventually cracking the heat exchanger from thermal stress.
Montgomery County's WSSC water averages 120-140 mg/L hardness — moderately hard. Rockville's Potomac River water runs higher. Over 12 months without descaling, a typical family-of-four install will accumulate enough scale to reduce efficiency by 5-10%. Over 3 years it can crack the heat exchanger entirely — a $2,000+ warranty event.
The annual maintenance schedule
| Task | Frequency | Time | DIY or Pro |
|---|---|---|---|
| Heat exchanger descaling (flush) | Every 12 months | 45-60 min | DIY or Pro |
| Air filter vacuum | Every 6 months | 2 min | DIY |
| Condensate trap check | Every 6 months | 30 sec | DIY |
| Gas connection inspection | Every 24 months | 10 min | Pro |
| Venting inspection | Every 36 months | 15 min | Pro |
| Error log review | Monthly | 30 sec (app) | DIY |
How to descale a tankless water heater
Descaling (also called "flushing") is the core annual maintenance task. You can hire us to do it for $150 flat, or do it yourself in about an hour. Here's the short version:
- Shut off gas and power. Safety first. Close the gas valve, unplug the unit.
- Close cold and hot isolation valves. The hot/cold shutoffs that came with your install.
- Connect hoses to service valves. Inlet hose from a 5-gallon bucket, outlet hose draining back to the bucket. (This is only possible if you have service valves installed — which is why we install them on every unit.)
- Fill bucket with descaling solution. 3-4 gallons of white vinegar OR a commercial citric acid solution.
- Run a submersible pump for 45 minutes. Recirculates the solution through the heat exchanger, dissolving scale.
- Flush with fresh water. Run clean water through for 5 minutes to remove solution residue.
- Restore service valves, gas, and power. Fire the unit, verify normal operation.
DIY cost: ~$60 (vinegar + one-time $100 pump kit, amortized). Professional cost: $150-195 in Montgomery County. We include the first-year flush in every install.
Don't want to DIY the flush?
Book annual professional maintenance — $150 flat in Montgomery County. Includes descaling, filter check, and error log review.
Air filter check — the 2-minute task most people skip
Most condensing tankless units pull combustion air through a small filter to protect the burner. In basement or garage installs, this filter clogs with dust within 6-12 months. Clogged = inefficient combustion and eventually error codes.
- Remove the front cover (usually 2-4 screws)
- Locate the air filter — a small mesh or foam screen near the air inlet
- Vacuum with a soft brush attachment, or rinse with water and dry
- Reinstall and close cover
Total time: 90 seconds. Do this every 6 months.
Condensate trap check
High-efficiency condensing tankless units produce a few gallons of acidic condensate per day. This drains through a small PVC line, often tied into your utility sink or basement floor drain. Rarely, the line clogs with debris or grows algae — especially in warm summers.
Every 6 months, trace the condensate line. Confirm water flows out when the unit runs. If you see standing water or pooling near the unit, the drain is clogged — clear it with a small pipe brush or call us.
Common error codes
Modern tankless units display numeric error codes when something goes wrong. Here are the ones we see most often in Montgomery County:
| Code | Meaning | First thing to try |
|---|---|---|
| 10 / 11 | Exhaust blocked or vent issue | Check exterior vent for snow, leaves, bird nest |
| 12 | Flame failure | Verify gas supply (try gas range — if that works, call us) |
| 14 | Overheat | Descale the unit — almost always scale-related |
| 16 | Water temperature too high | Check for mixing valve failure; descale |
| 25 | Condensate drain issue | Check and clear condensate line |
| 29 | Condensate level sensor | Clear condensate trap and line |
| 65 | Flow sensor | Descale the unit — mineral buildup on sensor |
| 76 | Communication error (remote) | Check remote wiring; often loose connector |
Anything not listed here is worth a call — we can usually diagnose it in two minutes over the phone before dispatching a tech.
Hard water defense strategies
If you're in Rockville, Potomac, or any other WSSC service area with moderately hard water, three strategies extend tankless lifespan significantly:
- Whole-house water softener. $1,500-$2,500 installed. Reduces scale buildup by 80%+. Pays for itself in extended unit life AND extends dishwasher/washing machine life. Our most common upgrade recommendation for Potomac homes.
- Descaling schedule discipline. Annual without fail — twice yearly in very hard water areas.
- Template-assisted crystallization (TAC) filter. Salt-free alternative to a softener. $800-1,200 installed. Less effective than a true softener but lower maintenance.
If you're not sure how hard your water is, WSSC publishes the hardness for every zone on their website — or we'll test yours during the consult, no charge.
Common problems and fixes
Lukewarm water
Most common cause: unit is undersized for simultaneous demand. Second most common: scale buildup reducing heat transfer. Third: gas pressure issue. Start with a descale; if that doesn't fix it, call us.
Cold water sandwich
Brief cold burst when you turn on hot water, caused by leftover cooled water in the pipes. Solution: run water for 3-5 seconds before use, OR install recirculation (Signature tier includes this by default).
Fluctuating temperature
Usually minimum-flow threshold issue — a dribbling tap below 0.5 GPM doesn't maintain burner firing. Usually fixed by opening tap slightly more.
Unit won't ignite
Check gas supply first (does your gas stove work?). If yes, check error code on the display. Flame rod fouling is a common cause and requires pro service.
Noisy operation
Clicking is normal (gas valve cycling). Rumbling or scraping = descale needed. High-pitched whistle = venting issue, call us.
If none of the above describes what you're seeing, send us a short video or photo by text — we can usually name the problem from a 10-second clip.
When to call a professional
DIY works for annual descaling, filter cleaning, condensate checks, and basic error code resets. Call us for:
- Any error code that returns after a reset
- Gas supply issues of any kind
- Venting problems (especially after storms or exterior renovation)
- Water leaks anywhere on the unit
- Unit failure within the warranty period (we handle the claim)
- Major performance drop that a descale didn't fix
- Annual service if you don't want to DIY the flush
Next steps
- Bookmark this page and revisit it every spring
- Order a flush kit from Amazon (~$100) if you plan to DIY
- Re-read the flush section above the first time you do it — it's the only part that's fiddly
- Keep the error code table handy for when a code pops up on the unit
- Or just let us handle it — $150 flat, once a year