Noritz Leaking From the Bottom
The Short Answer: Water under a Noritz is not one failure. Cool acidic drip from the condensate trap is plumbing, not a dead exchanger. Hot water from the brass PRV is pressure. A weep at the inlet filter or drain plug is a gasket. Water from inside the jacket with those dry is often the heat exchanger — shut it down. Do not run a wet PCB.
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Search Intent & The Real Problem
You looked under an NRC, EZ, NRCP, or NCC and found a puddle. Indoor condensing Noritz units hide three wet systems in one case: potable water, condensate, and the T&P. Outdoor non-condensing units add rain and freeze-drain. Treating all of them as “the tankless is shot” is how people buy a $1,600 exchanger because a filter cap was a quarter-turn off.
Sister leaks: Navien from the bottom, Takagi leaking, tankless draining.
What other guides get wrong
They call condensate “a leak” and pinch the drain hose. A pinched Noritz condensate line overflows into the cabinet and takes the board with it. They skip temperature: condensate is cool; PRV water is house-temp to hot; an exchanger leak is usually hot and from inside the jacket. They also treat the hex drain plug at the bottom of the waterway as a mystery leak when someone cracked it a quarter turn “to flush.”
Step-by-Step Troubleshooting
Step 1: Identify the fluid
| Clue | Source | Next |
|---|---|---|
| Cool, only while the burner runs, from the PVC / trap | Condensate — normal if piped, a leak if the joint failed | Trap, slope, union |
| From the brass T&P, pulses on a heat call | Pressure / expansion — typical relief 150 psi / 210°F | Gauge the house; never cap |
| Filter cap, polymer housing, or isolation-valve packing | Service-valve O-ring or stem | Cap / packing |
| Hex drain plug at the bottom of the waterway | Plug not seated, missing gasket | Snug with the unit isolated — do not gorilla |
| Hot, from inside the cabinet, exchanger, or bottom pan with fittings dry | Potable leak — exchanger or internal fitting | Shut down |
| Only after rain, outdoor unit | Wind-driven rain or a missing cap | Not an exchanger until the cabinet is dry on a clear day |
- What to look for: Dry it. Run one hot faucet. Wipe again. Cool vs hot tells you condensate vs potable before you buy parts.
- Required tools: Paper towel, flashlight.
Step 2: Condensate path on NRC / EZ condensing units
- What to look for: Trap full, drain run uphill, frozen termination, loose union at the cabinet, spent neutralizer media backing water into the case. Indoor NRC1111-class units will wet the pan and look exactly like a “bottom leak.” Non-condensing NR / older outdoor units should not make a steady cool stream — if they do, look at rain and freeze-drain, not a condensate trap they do not have.
- Required tools: Wet/dry vac on the external drain only.
Clearing an external trap is DIY. Water behind the cover on the PCB is not. Same overflow physics as Navien condensate.
Step 3: PRV versus exchanger
- What to look for: T&P on the hot outlet with a discharge pipe. If that pipe is dry and the cabinet is wet, you are past “just a valve.” White scale trails down the exchanger, or a drip from the bottom pan with isolation valves closed (after residual drains), points at the exchanger or a cracked internal waterway. House static over ~80 psi with a waterlogged expansion tank will lift a healthy PRV every fire — expansion tank full of water, Rinnai T&P.
- Required tools: Isolation valves, hose-bib gauge.
Close cold and hot isolation. If it still weeps from inside after the unit depressurizes, that water is from the exchanger or an internal fitting.
Step 4: Inlet filter, isolation valves, drain plug
- What to look for: Cylindrical inlet screen housing on the cold service valve. Cap not seated, cracked polymer, missing O-ring. Isolation-valve stem packing that weeps down the front and pools at the feet. Factory drain plug at the bottom of the heat-exchanger waterway — a hand-tight plug after a “flush” is the most common save I make on a Noritz that “leaks from the bottom.”
- Required tools: Eyes on the cold-side service assembly. Isolation off before you touch a plug.
A new O-ring is a parts-store save. A cracked heat exchanger is a licensed replacement — often the whole unit if Noritz does not sell that year’s exchanger separately.
Step 5: Freeze, overpressure, and when the board is already wet
- What to look for: Outdoor unit that iced, garage that hit 15°F with power off. Freeze-split exchangers leak from the bottom on the first thaw. Power off overnight to “save electricity” is how those splits happen. Outdoor drip only in a storm is rain, same family as leaking by the exhaust. Wet board, error codes after the leak, or a stream you cannot name: isolate and hire it.
- Required tools: Freeze history, hose-bib gauge. Do not purge the gas line.
When DIY Ends: Calling a Licensed Pro
Stop at a wet PCB, a stream from inside the jacket, gas smell, or a freeze-split exchanger. You may snug a condensate union, clean an external trap, reseat a filter cap, and confirm a drain plug is actually tight after isolation. Heat-exchanger diagnosis, combustion, and replacement are licensed. Noritz will not smile on an exchanger that ran with a blocked condensate line or a unit that froze with the breaker off.
Frequently Asked Questions
Q: Why is my Noritz leaking from the bottom? A: Condensate overflow, a loose drain fitting, T&P discharge, a filter housing or drain plug, or a heat exchanger. Identify whether the water is cool condensate or hot potable before you buy parts.
Q: Can I keep using a Noritz that drips from the bottom? A: Not if the cabinet or board is wet, and not if the exchanger is the source. Condensate at a proper drain can wait a day. Internal potable leaks cannot.
Q: Is a Noritz heat-exchanger leak repairable? A: Internal exchanger leaks are replacement of the exchanger or the unit. External fittings, the condensate trap, the filter cap, and the drain plug are repairable. Do not epoxy the exchanger.