Descale interval by FL county GPG • Step-by-step flush • Rinnai • Navien • Rheem • Noritz error codes
Calculate Your Descaling Interval
Florida's hard water accelerates scale buildup inside tankless heat exchangers. Your descaling interval depends on your county's water hardness (GPG) and your usage patterns. Scale buildup reduces efficiency and triggers error codes — use this calculator to stay ahead of it.
Your Recommended Descaling Interval
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months
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Water Hardness (GPG)
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Hardness Category
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Next Descaling Due
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Vinegar Volume Needed
Florida County Water Hardness Reference
County
GPG
Hardness
Flush Every
Collier
17.5
Extreme
6 mo
Miami-Dade
15.5
Extreme
6–7 mo
Palm Beach
14.5
Very Hard
7–8 mo
Lee
14.0
Very Hard
7–8 mo
Monroe (Keys)
14.0
Very Hard
7–8 mo
Broward
13.5
Very Hard
8 mo
Charlotte
12.5
Very Hard
8–9 mo
Osceola
10.0
Hard
10 mo
Sarasota
10.0
Hard
10 mo
Orange
9.0
Hard
11 mo
Hillsborough
6.5
Moderate
14 mo
Pinellas
5.5
Moderate
16 mo
Duval
4.5
Moderate
18 mo
Flush intervals assume no softener, medium household usage. Softener reduces interval by 40–60%.
Scale Buildup — What It Costs You
1/16" scale (early)12% efficiency loss — $15–25/mo extra gas cost
1/8" scale (moderate)25% efficiency loss — error codes beginning
3/16" scale (heavy)40% efficiency loss — frequent shutdowns
1/4" scale (severe)Heat exchanger replacement — $400–$900 part
Full scale blockUnit failure — replace entire unit $800–$2,500
Annual descaling cost$120–$280 (DIY: $15 in vinegar)
Heat exchanger warranty noteMost warranties void if scale damage — no flush records
Step-by-Step Tankless Descaling Flush
⚠️ Before starting: This procedure applies to tankless units with service valves / isolation valves on the cold inlet and hot outlet. If your unit lacks these valves, a plumber must install them before descaling is possible. Most FL installations include them, but pre-2015 installs sometimes do not.
Total procedure time: 60–90 minutes. Best done with a partner. Works on all major brands (Rinnai, Navien, Rheem/Ruud, Noritz, Bosch, Takagi).
Equipment You Need
🪣
5-Gallon Bucket (food-grade)
Must hold solution during recirculation — food-grade keeps vinegar uncontaminated. ~$8 at hardware store.
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Submersible Utility Pump
1/6 HP or greater — pumps vinegar through heat exchanger. Rental option: ~$15/day at hardware stores. Purchase: $35–$65. Harbor Freight 1/6 HP utility pump works well.
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White Distilled Vinegar — 1–2 gallons
Acetic acid dissolves calcium carbonate scale without damaging heat exchanger internals. Use 5% white vinegar (standard grocery store). Never use apple cider or cleaning vinegar — additives can damage seals. For S. FL extreme hard water: 2 gallons recommended.
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Two Descaling Hoses with 3/4" Garden Hose Fittings
One hose: pump outlet → cold inlet service valve. Second hose: hot outlet service valve → bucket (return). Most units have 3/4" FHT (female hose thread) on service valves. Often sold as "descaling kit" — $15–$25 on Amazon.
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Rubber Gloves
Vinegar is food-safe but irritating to eyes. Gloves protect from spills. Safety glasses recommended.
Descaling Procedure — Step by Step
1
Turn Off the Gas / Power Supply
For gas units: turn off the gas shut-off valve on the gas supply line to the water heater. For electric tankless: switch the dedicated circuit breaker to OFF. The unit must be fully de-energized before disconnecting any water connections. Verify the unit is off — no pilot light (gas), no status lights (electric).
⏱️ Time: 2 minutes
2
Close the Cold Water Inlet and Hot Water Outlet Service Valves
Your tankless unit has two service valves (also called isolation valves): one on the cold water inlet (typically with a blue handle or labeled "cold") and one on the hot water outlet (red handle or labeled "hot"). Close both valves by turning them perpendicular to the pipe. This isolates the unit from your household water supply so you can flush with vinegar without contaminating house lines.
⏱️ Time: 2 minutes
⚠️ If your unit lacks service valves: do NOT proceed — call a plumber to install them first. Proceeding without service valves will pump vinegar into household supply lines.
3
Release Pressure — Open a Hot Water Faucet
Open a nearby hot water faucet (bathroom sink works well). This releases residual pressure in the hot water lines so you can disconnect the service valve ports without water spraying. Leave the faucet open throughout the procedure — the house hot water system is now isolated at the unit's service valves, so no water flows. Close the faucet after pressure releases (10–15 seconds).
⏱️ Time: 1 minute
4
Connect the Descaling Hoses
Service valves typically have a port cap (flush port) — remove the caps on both the cold inlet service valve and hot outlet service valve. Connect your first hose from the submersible pump outlet to the cold inlet flush port (this is where vinegar enters — cold side pushes solution through the heat exchanger). Connect your second hose from the hot outlet flush port to your bucket (this is the return line — vinegar exits here after traveling through the heat exchanger). Place the pump inside the 5-gallon bucket with the return hose. The bucket is the vinegar reservoir.
⏱️ Time: 5–10 minutes
5
Fill Bucket with White Vinegar and Start Pump
Pour 1 gallon of white distilled vinegar into the 5-gallon bucket. For S. FL extremely hard water (Collier, Miami-Dade), use 1.5–2 gallons. Place the submersible pump in the bucket. Open the flush port valves on both service valves (the main valves remain closed). Start the pump. Vinegar will circulate: bucket → pump → cold inlet → through heat exchanger → hot outlet → return hose → bucket. You should see flow within 30 seconds. Scale particles and discolored solution (tan/brown) will appear in the bucket within 5–10 minutes.
⏱️ Time: 5 minutes to set up; then run for 45–60 minutes
⚠️ If little or no flow: check hose connections and flush port valves are fully open. A blocked heat exchanger may restrict flow significantly — this confirms descaling is overdue.
6
Circulate for 45–60 Minutes
Allow the pump to circulate vinegar continuously for 45–60 minutes. For moderately scaled units: 45 minutes is typically sufficient. For heavily scaled units (S. FL counties, infrequent service): run 60 minutes, then drain and repeat with fresh vinegar for another 30 minutes. The solution in the bucket will turn progressively darker and more cloudy as scale dissolves — this is normal and confirms the flush is working. If solution remains clear and colorless after 20 minutes, the unit may be lightly scaled or already descaled.
⏱️ Time: 45–60 minutes (or up to 2 hours for severely scaled units)
7
Stop Pump, Drain Vinegar, Flush with Fresh Water
Turn off the pump. Close the flush port valves. Disconnect the hoses. Replace the flush port caps. Open the cold inlet main service valve slowly — fresh water will push remaining vinegar through the unit and out the open hot water faucet (open a hot tap for this step). Allow to flush for 3–5 minutes until water runs clear and odor-free. Then open the hot outlet main service valve to restore full flow to household lines.
⏱️ Time: 10 minutes
8
Restore Power / Gas and Test
Restore gas supply (open gas shut-off) or turn on the circuit breaker for electric units. Check for any error codes on the display — a successful descale should clear LC (Rinnai), scale-related error codes (Navien, Rheem, Noritz). Turn on a hot water fixture. Unit should ignite within 3–5 seconds and maintain stable flow and temperature. If error codes persist, the unit may require professional service — some scale damage is non-reversible with a DIY flush.
⏱️ Time: 5 minutes
💡 Record the date of this flush — set a calendar reminder for your next interval (see Descale Interval tab).
Post-Flush Checklist
✅ Both service valves fully openMain valves — not flush port valves
✅ Flush port caps replacedPrevents slow drip leak at port
✅ No vinegar odor at hot tapsRun hot water 2–3 minutes to fully clear
✅ No error codes on displayClear display = successful descale
✅ Unit ignites promptly3–5 second ignition; no stuttering
✅ Flush date recordedLog date for next service interval calculation
Tankless Water Heater Scale Error Codes
These error codes indicate scale buildup or scale-triggered temperature problems in Florida's hard water conditions. Look up your brand and code to determine if a DIY descale will resolve it or if professional service is needed.
💡 Florida's high-GPG water accelerates scale buildup — most FL tankless units encounter scale codes 2–3× faster than national averages. If your unit shows any of these codes, schedule descaling immediately regardless of your last service date.
Rinnai — Scale / Lime Error Codes
RINNAI
LC / LC0 Descale Now
Scale (Lime / Calcium) Reminder — Code LC or LC0
The Rinnai LC code is a preventive maintenance reminder triggered by the unit's internal flow-hour counter after a preset interval. LC0 = first warning. The unit continues to function normally at this stage. This is NOT a fault code — it's a reminder that descaling is overdue based on usage hours. In FL hard water counties, LC0 typically triggers at 6–8 months of use, well before the unit's own preset interval.
✅ Fix: Perform descaling flush (see Flush Guide tab). After flush, reset LC code: press and hold the On/Off button for 5 seconds until code clears. Reset procedure varies by model — check your owner's manual.
RINNAI
LC1–LC9 Service Needed
Progressive Scale Accumulation Codes
LC1 through LC9 indicate increasing scale accumulation detected by the unit's internal sensors. Each step represents progressive restriction in the heat exchanger. LC1–LC3: descaling typically resolves the issue. LC4–LC6: scale is significant — descaling may partially restore performance but professional service is recommended to verify heat exchanger condition. LC7–LC9: severe scale accumulation. Heat exchanger damage may have occurred. Professional service required — descaling alone may not be sufficient. In S. FL extreme hard water (Collier, Miami-Dade), units can progress from LC0 to LC5 within 12–18 months without descaling.
⚠️ LC1–LC3: Descale immediately. LC4+: Call for professional service. Do not delay — higher LC codes indicate potential heat exchanger damage that cannot be reversed by flushing.
RINNAI
Code 16 Service Needed
Overheating — Often Scale-Induced in FL
Code 16 indicates the unit has overheated. In Florida, Code 16 on Rinnai units is frequently caused by scale-restricted heat exchanger rather than true overheating from ambient conditions. Scale reduces water flow through the heat exchanger, causing the water that does pass to overheat. If Code 16 appears and your last descale was more than 6 months ago in an S. FL county, descaling is the likely fix.
First: attempt descaling flush. If Code 16 clears after flush, scale was the cause. If Code 16 returns within days of descaling, heat exchanger or temperature sensor damage may be present — call for professional service.
Navien — Scale-Related Error Codes
NAVIEN
E003 Service Needed
Ignition Failure — Can Be Scale-Induced
Navien E003 indicates the unit failed to ignite after multiple attempts. While E003 has multiple causes (gas supply, igniter, flame rod), scale-induced flow restriction is a common FL cause: scale reduces water flow below the unit's minimum activation threshold, preventing ignition. If gas supply is confirmed good and the igniter has no visible damage, scale restriction is the likely culprit in hard water areas. E003 in FL commonly co-occurs with or follows ignoring E016 (heat exchanger temperature) for an extended period.
Check: (1) Confirm gas supply is on and at adequate pressure. (2) If gas OK: descale the heat exchanger — flow restriction preventing ignition is common in FL hard water. (3) If E003 persists after descale: igniter or flame rod service required.
NAVIEN
E012 Descale Now
Heat Exchanger Outlet Temperature Too High
Navien E012 indicates the outlet temperature sensor is reading excessively high temperature. In FL hard water conditions, E012 is almost always caused by scale restricting flow through the heat exchanger — less water flows, same BTUs heat it, result is overheating at the outlet. This is the single most common hard-water scale error code in FL Navien units. E012 in Palm Beach, Collier, or Miami-Dade county with no prior descaling = scale is nearly certain cause.
✅ Primary fix: Descale the heat exchanger immediately. E012 typically clears immediately after a complete descaling flush. If E012 recurs within 30 days of descaling, heat exchanger or temperature sensor may be damaged — call for service.
NAVIEN
E016 Descale Now
Abnormal Heat Exchanger Outlet Temperature
E016 is Navien's direct scale-detection error — triggered when heat exchanger outlet temperature exceeds safe limits, a reliable indicator of calcium scale coating the heat exchanger surface. Unlike E012 (which can have other causes), E016 in Florida's hard water climate is almost exclusively caused by scale. Navien recommends descaling as the first response to E016. Units in S. FL on municipal water without a softener commonly trigger E016 at 6–10 month intervals.
✅ Fix: Descale immediately. E016 will clear after a complete flush. After descaling, consider a water softener or Navien's optional NaviCirc recirculation setup to reduce scale velocity at the heat exchanger.
Rheem / Ruud — Scale-Related Error Codes
RHEEM / RUUD
P1 Descale Now
Scale / Lime Reminder Code
Rheem P1 is a maintenance reminder code indicating descaling is due based on usage hours and flow monitoring. Similar to Rinnai's LC code — the unit continues to operate but flags that scale maintenance is overdue. In FL hard water counties, P1 typically triggers ahead of the national schedule. Rheem RTGH-series and Performance Platinum tankless models commonly show P1 within 6–8 months of installation in S. FL without a water softener.
✅ Fix: Perform descaling flush. After flush, reset P1 code — consult your specific model's manual for reset procedure (typically involves accessing service mode via control buttons).
RHEEM / RUUD
Code 13 Service Needed
Exhaust High-Limit — Can Be Scale-Induced
Rheem Code 13 indicates exhaust temperature exceeded safe limits. While often a venting issue (blocked vent, improper vent length), in FL it can be scale-induced: a scaled heat exchanger transfers heat less efficiently, causing excess heat to reach the exhaust. If venting is confirmed clear and unobstructed, inspect and descale the heat exchanger. Code 13 + P1 together = almost certainly scale-related.
Check: (1) Inspect vent termination — clear of obstructions, birds nests, debris (common in FL). (2) If vent is clear: descale heat exchanger. (3) If Code 13 persists after descale: call for professional exhaust temperature sensor or heat exchanger service.
RHEEM / RUUD
C7 Professional Service
Condensate Drain Issue — Scale Can Block Drain
Rheem condensing tankless units (condensing models) produce acidic condensate that drains through a condensate drain line. Scale deposits from FL hard water can block this drain line, triggering C7. A blocked condensate drain allows acidic water to pool inside the unit, accelerating internal corrosion. C7 is more common in FL than in other regions due to hard water mineral deposits combining with condensate to form scale deposits in the drain.
Inspect condensate drain line — clear any calcium deposits or blockage. Flush drain line with vinegar. If condensate pan overflow is visible, call for professional service to assess internal condensate drainage and scale deposit removal.
Noritz — Scale-Related Error Codes
NORITZ
Code 11 Service Needed
No Ignition / Flame Failure — Scale-Triggered in FL
Noritz Code 11 indicates ignition failure. In FL hard water areas, Code 11 on Noritz units frequently results from scale-induced flow restriction below the minimum flow rate required for ignition (typically 0.5 GPM). As scale narrows the heat exchanger passage, flow slows below the activation threshold — the unit attempts to ignite but shuts down safely. This presents as Code 11 even though the ignition system is intact. Common in Noritz units installed in Palm Beach, Collier, Broward counties after 12–18 months without descaling.
First check: gas supply adequate. If gas is OK → descale heat exchanger. Code 11 from flow restriction will clear after descaling restores proper flow rate through the heat exchanger.
NORITZ
Code 12 Service Needed
Flame Failure During Operation
Code 12 indicates the flame extinguished during a hot water demand cycle. In FL, scale-restricted flow is a common cause — the unit ignites successfully but flow restriction causes the activation threshold to drop below minimum during the cycle, extinguishing the burner. This presents as intermittent hot water — sometimes works, sometimes drops out mid-use with Code 12. Descaling typically resolves Code 12 when scale-induced flow restriction is the cause.
Descale the unit. If Code 12 persists after descaling, the flame rod, igniter, or gas valve may require professional service.
NORITZ
Code 73 Descale Now
Scale / Water Quality Alert
Noritz Code 73 is the direct scale maintenance reminder, triggered by the unit's internal usage and flow monitoring. It indicates scale buildup has reached a level where the unit's performance is affected. Code 73 in FL hard water conditions (above 10 GPG) typically triggers within 8–12 months of installation without descaling or water softening. Noritz recommends immediate descaling when Code 73 appears. Unlike some brands, Code 73 does not automatically reset after a flush — must be manually cleared in service mode.
✅ Fix: Descale immediately. After flush, access service mode to reset Code 73 counter — procedure varies by Noritz model. Consult owner's manual or Noritz technical support for reset steps (typically: hold Up + OK simultaneously for 5 seconds in off state).
Schedule Professional Tankless Descaling
💧 Our licensed FL plumbers perform professional tankless descaling with equipment-grade flush systems, post-flush performance verification, and error code reset. We also install service valves if your unit lacks them. Serving South Florida — same-week scheduling available.