How to Flush & Descale a Noritz Tankless

Descaling is the most important Noritz maintenance task. Scale insulates the heat exchanger, reduces output, raises gas bills, and eventually triggers Code 14 (overheat). The ecoTOUGH stainless heat exchanger is more scale-tolerant than competitor units, but not maintenance-free.

Tools needed

• Submersible pump kit ($40-60 on Amazon)
• Two 5-gallon buckets
• 4 gallons of white vinegar OR 1 gallon of commercial descaler (Noritz-branded; Hercules Sizzle, CLR PRO also work)
• Two ¾" garden hoses
• Crescent wrench

Prep

1. Turn off the gas at the unit's shutoff valve
2. Close the cold-water inlet isolation valve
3. Close the hot-water outlet isolation valve
4. Open a hot tap to release residual pressure
5. Allow 10 minutes for the unit to cool

Connect the pump

1. Attach one hose to the cold-side isolation valve service port
2. Drop the hose into a bucket containing descaler
3. Attach the second hose to the hot-side service port
4. Drop the hot hose into the same bucket (closed loop)
5. Connect the submersible pump to the cold-side hose; place pump in bucket

Run the descale

1. Open both isolation valve service ports
2. Verify main isolation valves are closed
3. Plug in the pump
4. Circulate descaler for 45-60 minutes
5. Fluid will discolor; may foam — scale dissolving

Rinse

1. Unplug the pump
2. Close the cold-side service port
3. Disconnect the cold-side hose
4. Open the cold-water main isolation valve briefly to flush fresh water through the system, exiting via the hot-side hose into a clean bucket — 5-10 gallons until water runs clear
5. Close the hot-side service port; disconnect the hot hose
6. Open both main isolation valves

Restart

1. Open a hot tap; run until flow is steady (no air)
2. Turn the gas back on
3. Power-cycle the unit if any error code appears
4. Verify normal operation under draw

EZTR recirculation pump consideration

For EZTR units with built-in recirculation pump, the descaling procedure includes the recirc pump in the closed loop. The pump may need extra rinsing to fully clear residual descaler — extend the rinse cycle by 2-3 minutes for EZTR models.

Cascade descaling (NCC commercial)

For NCC cascade installs, descale units one at a time:

1. Use cascade controller to isolate the target unit (other units stay online)
2. Close the unit's individual isolation valves
3. Run the standard descaling procedure on the isolated unit
4. Rinse and restore
5. Bring the unit back into the cascade via the controller
6. Move to the next unit

This maintains hot water availability during the maintenance window — critical for hotels, restaurants, multi-unit residential.

Vinegar vs commercial descaler

Vinegar is cheaper but slower. Commercial descaler (Noritz-branded, CLR PRO, Hercules Sizzle) is faster, stronger, food-safe. For routine annual: vinegar is fine. For first-time descale on a scaled unit: commercial descaler.

How often

Hard water (>11 gpg) — annually. Soft water (<7 gpg) — every 2 years. With a softener — every 3 years. Commercial NCC in restaurant duty — every 6-9 months in hard water.

Bottom line

Document with dated photos for warranty defense. For NCC cascade installs, schedule individual unit descaling as part of an annual service contract — the cascade controller's isolation makes this minimally disruptive to operations.