Noritz Water Heater Leaking

Common Symptoms

• Water dripping from the bottom of the Noritz unit — steady drip or puddle
• White residue or mineral deposits on or around the condensate drain line (NRC/NRCP)
• Water pooling under the unit — may be intermittent, only when unit is running
• T&P (temperature and pressure) relief valve dripping from discharge pipe
• Wet staining or corrosion at inlet or outlet pipe unions
• Error 90 appearing alongside reduced output and visible moisture (heat exchanger leak)
• Water inside the unit enclosure — visible when the front panel is removed
• Pipe connections wet only after freeze-thaw events

Most Likely Causes

1. 1

   Condensate Drain Line Leak (Condensate Neutralizer Maintenance — NRC/NRCP)

   Noritz NRC and NRCP condensing models extract heat from exhaust gases, producing acidic condensate (pH 3–4) that drains through a dedicated condensate drain line. Leaks from this drain occur in several ways: (1) The condensate neutralizer cartridge (which raises condensate pH with limestone chips before it enters the drain) becomes saturated with calcium carbonate and backs up flow, causing overflow at the condensate collection tray. Noritz recommends replacing the neutralizer annually or when chips appear exhausted (visually reduced volume). (2) The condensate drain hose develops a crack, kink, or loses its slip-joint fitting seal. (3) The condensate tray itself cracks from freeze-thaw cycles. A condensate-drain leak leaves a white mineral residue trail on the floor — distinguishable from other leaks by the chalky deposit. Unresolved condensate backup can also trigger Error 90 by impairing the condensing heat exchanger's ability to shed heat.

2. 2

   Pressure Relief Valve Drip (Test and Replace, Expansion Tank)

   The T&P (temperature and pressure) relief valve is a safety device that vents when water pressure exceeds 150 PSI or water temperature exceeds 210°F. Occasional dripping from the T&P discharge pipe can mean: (1) The valve is functioning correctly — pressure is spiking above the set point due to thermal expansion in a closed plumbing system (no expansion tank, or a failed expansion tank). This is common in homes with a backflow preventer or PRV on the main — they create a closed system where heated water has nowhere to expand. Installing or replacing an expansion tank eliminates this. (2) The valve seat is worn or scaled and is dripping at normal operating pressure — the valve must be replaced. (3) The discharge pipe is oversized, horizontal, or incorrectly terminated, creating back-pressure that allows water to siphon. Never plug or cap the T&P discharge pipe — this is a code violation and safety hazard.

3. 3

   Inlet/Outlet Connection Leak (Union Fittings, Teflon Tape + Pipe Dope)

   Noritz units use union fittings at the cold inlet and hot outlet connections to allow service removal without cutting pipes. These unions can develop leaks from: (1) Worn union O-ring or gasket — the union nut's rubber seal degrades over time, especially with hard water mineral scaling. Remove the union nut, inspect the O-ring, and replace if cracked or deformed. (2) Improper thread sealant — if threaded connections upstream or downstream of the union were sealed with Teflon tape only, vibration and thermal cycling can cause tape to shred and pack into threads without sealing. Use Teflon tape plus yellow gas-rated pipe dope on all threaded water connections for a durable seal. (3) Dissimilar metal corrosion — aluminum and copper connections at the unit manifold can develop galvanic corrosion around threaded joints in high-chloride water areas; dielectric unions prevent this.

4. 4

   Flow Sensor O-Ring Leak

   The flow sensor on the Noritz cold inlet manifold contains an O-ring that seals the sensor body against the manifold housing. If this O-ring dries out, hardens, or is displaced during service, a slow leak develops at the sensor body-to-manifold junction. This leak is typically minor (one drop per minute or less) but will worsen if ignored. Replacement involves: closing the cold supply and hot outlet isolation valves, depressurizing the unit, removing the flow sensor body (typically one to two screws), replacing the O-ring with the correct silicone O-ring for your Noritz model, applying a thin layer of silicone grease to the new O-ring before installation, and reinstalling. Do not use petroleum-based lubricants on silicone O-rings as they degrade the rubber.

5. 5

   Freeze Damage (Built-In Freeze Protection, Isolation Valve Procedure)

   All Noritz tankless models include built-in freeze protection — small electric heaters in the water passages that activate at approximately 37°F to prevent ice formation when the unit is powered but not actively heating. However, the freeze protection only works when the unit has power. If the unit is unplugged or loses power during freezing temperatures, or if the ambient temperature drops below the freeze protection capability (below approximately 10°F), ice can form in the heat exchanger, cracking the copper or stainless steel passages. Freeze damage typically appears as a leak at the heat exchanger body or inlet/outlet manifold that begins when the unit thaws. Proper winterization when the unit will be de-powered: (1) Turn off the cold supply isolation valve. (2) Open the hot outlet isolation valve and attach a small air compressor to the cold service port to blow out residual water. (3) Leave the isolation valves open to allow any residual water to drain. Never use propylene glycol antifreeze — Noritz specifically prohibits antifreeze in the water passages.

6. 6

   Scale-Perforated Heat Exchanger (Descale vs. Replace Decision Tree)

   The most serious Noritz leak scenario is a pinhole or crack in the condensing heat exchanger body caused by stress from extreme scale buildup. When scale accumulates inside the heat exchanger passages, it causes repeated thermal overheat cycles (Error 90 → Error 14 sequence) that fatigue and eventually perforate the stainless steel or copper heat exchanger wall. Signs: Error 90 plus a visible water leak from the heat exchanger body (water dripping from the unit even when isolation valves are closed), or discolored water with rust or scale particles. Decision tree: (1) If the perforation is confirmed by closing both isolation valves and water continues to drip — the heat exchanger is perforated and replacement is required. (2) If the unit is less than 7 years old and the heat exchanger is the only failed component, replacing the heat exchanger is cost-effective ($400–$700 parts + labor). (3) If the unit is over 10 years old or the heat exchanger is unavailable, full unit replacement is the better long-term value. Installing a whole-house water softener or polyphosphate scale inhibitor prevents recurrence.

Quick DIY Checks

1. 1Step 1 — Identify the leak source before touching anything: place dry paper towels under the unit and on the floor in front of it. Run a hot water draw for 2 minutes and observe where the first drops appear. Key clues: drips at the bottom center of the unit with a white chalky deposit = condensate drain (NRC/NRCP only). Drips from a pipe exiting the wall below the unit = T&P relief valve discharge. Wet staining at the pipe connections left and right of the unit = union fittings. Drip at the lower front of the unit that appears only when running = flow sensor O-ring. Moisture inside the unit enclosure at the heat exchanger body (remove front panel to check) = heat exchanger leak. Identify the source before proceeding — each has a different repair.
2. 2Step 2 — Condensate drain inspection and neutralizer replacement (NRC/NRCP): locate the condensate drain line exiting the bottom of the unit and trace it to the condensate neutralizer cartridge (typically a white cylinder inline with the drain hose). Remove the neutralizer cartridge lid and inspect the limestone chip fill — if chips appear dissolved to less than half the original volume, the neutralizer is exhausted and must be replaced. Check the drain hose for kinks, cracks, or loose slip-joint fittings. Ensure the drain hose terminates in a floor drain or condensate pump — if it terminates into an open bucket, overflow causes floor flooding. Replace the neutralizer (Noritz recommends annual replacement in average use conditions).
3. 3Step 3 — T&P valve test and expansion tank assessment: locate the T&P valve (typically on the hot outlet manifold or hot supply pipe) and its discharge pipe. Carefully lift the test lever briefly (have a bucket ready — hot water will discharge) and release. If it re-seats cleanly with no drip after 10 seconds, the valve is functional and the drip is caused by system pressure — check the expansion tank. If it continues to drip after releasing the lever, the valve seat is worn and the valve must be replaced. Expansion tank check: press the Schrader valve on the expansion tank with a tire pressure gauge — correct pre-charge pressure is typically 50–80 PSI (match to your house static water pressure). If the tank releases water from the Schrader valve, the bladder is failed and the tank must be replaced.

1. 4Step 4 — Inspect and reseal union fittings: close the cold inlet and hot outlet isolation valves. Dry the union fittings completely with paper towel. Slowly crack the isolation valves open slightly and observe where moisture reappears. If water comes from the union nut face: tighten the union nut (do not overtighten — hand-tight plus 1/4 turn for plastic union nuts). If water persists, unscrew the union nut, remove and inspect the O-ring or flat washer — replace with an OEM-size silicone O-ring. Apply a thin film of Teflon paste (not plumber's grease) to the O-ring face before reassembly. For threaded joints beyond the union: disassemble, clean threads, apply 3 wraps of Teflon tape plus a bead of yellow pipe dope on the threads, reassemble, and torque to manufacturer spec.
2. 5Step 5 — Flow sensor O-ring replacement: close both isolation valves and open a hot tap to relieve pressure. Locate the flow sensor on the cold inlet manifold — it typically has a wiring harness connector and is held by 1–2 screws. Disconnect the harness, remove the screws, and pull the sensor body straight out. Inspect the O-ring in the groove on the sensor body — replace with a correctly sized silicone O-ring (bring the old one to the hardware store to match). Apply a thin film of clean silicone grease (not petroleum-based) to the new O-ring. Press the sensor body back into the manifold, reinstall screws, reconnect the harness, and restore water supply. Check for leaks.
3. 6Step 6 — Heat exchanger leak assessment (Error 90 + visible leak): close both isolation valves and wait 5 minutes. If water continues to drip from the heat exchanger body or manifold area, the heat exchanger is perforated and must be replaced or the unit must be replaced. Do not attempt to patch a perforated heat exchanger — pressurized patches fail rapidly. Contact Noritz warranty support (1-866-766-7489) to verify whether the unit is under warranty (NRC/NRCP models carry a 15-year heat exchanger warranty if the unit was registered and descaling was performed per schedule). If out of warranty, obtain a replacement heat exchanger quote from an authorized Noritz service center and compare to full unit replacement cost.

Repair vs Replace

Recommended Tools & Parts

• Noritz Condensate Neutralizer Cartridge

  Annual replacement cartridge for NRC/NRCP condensing models. Raises condensate pH from 3–4 to drain-safe levels using limestone chips.

  $20–$45

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• T&P Relief Valve (150 PSI / 210°F)

  Replacement temperature and pressure relief valve. Match to existing valve ratings — 150 PSI and 210°F are standard for tankless water heaters.

  $25–$50

  Buy on Amazon →

• Expansion Tank (2-gallon)

  Thermal expansion tank for closed plumbing systems. Prevents T&P valve from dripping by accommodating volume increase when water is heated.

  $30–$60

  Buy on Amazon →

• Silicone O-Ring Assortment

  Variety pack of silicone O-rings for union fittings and flow sensor replacement. Bring the old O-ring to match the correct size.

  $8–$15

  Buy on Amazon →

• Noritz Flow Sensor

  OEM replacement flow sensor for persistent flow sensor O-ring leaks or Error 65 flow sensor fault.

  $30–$70

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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