Noritz Code 29: Heat Exchanger High Limit Exceeded
Quick Answer
Noritz Code 29 indicates the heat exchanger has exceeded its safe temperature limit, often due to mineral scale buildup. The primary fix is to flush the unit with a descaling solution to restore proper heat transfer and water flow.
Code 29 is basically your Noritz waving a red flag before it throws Code 14, which is the real nightmare. Ignore it, keep resetting it, and you're betting against the thermal fuse. I see this mostly in homes with hard water that haven't been flushed in a couple years. The fix is usually a good vinegar flush, but only if you catch it before the fuse blows and the code changes to something way more expensive to deal with.
Phillips #2 screwdriver, Digital multimeter (resistance/ohms mode)
What Does the 29 Code Mean?
When a customer calls me with Code 29, they usually tell me the water starts hot but goes cold five minutes into a shower. That's because the heat exchanger can't shed heat fast enough. Whether it's calcium buildup acting like insulation or a slow flow rate, the metal's getting hotter than the water and the unit's shutting down to protect itself. Honestly, this is one of the more fixable codes on a Noritz if you catch it early.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Scale buildup on heat exchanger walls restricting water-side heat transfer40%
Water flow rate too low through the unit24%
NTC temperature sensor reading high (false positive)22%
Blocked condensate trap on NRCP condensing models14%
Symptoms You May Notice
Code 29 on the remote controller display, sometimes with a blinking LED on the unit itself.
Hot water starts strong then cuts out mid-shower, usually 3 to 8 minutes in depending on how bad the scale buildup is.
The unit fires up, you hear the burner ignite, then it shuts off and the water goes cold before you've finished rinsing.
Code 29 keeps coming back multiple times a day even after resetting, which tells you the underlying cause isn't going anywhere on its own.
Hot water output has gotten noticeably weaker over the past few months, like the unit's working harder just to keep up with normal demand.
Can you reset a Noritz waterheater to clear the 29 code?
Press the Power button on the remote controller once to turn it off, wait 10 seconds, then press it again. If that doesn't clear it, unplug the unit from the wall outlet for a full 60 seconds. Here's the thing: the heat exchanger needs time to physically cool down before the sensor resets. If Code 29 pops right back up after restart, give the unit 10 minutes to cool before you try again. Forcing restarts on a hot unit just stresses the thermal fuse closer to failure.
Tools Required for Diagnosis
Phillips #2 screwdriverDigital multimeter (resistance/ohms mode)Submersible pump (1/6 HP minimum)5-gallon bucket4 gallons food-grade white vinegar or Nu-Calgon descaling solutionGarden hose for flush rinsingSlip-joint pliers (for inlet screen removal)Pipe heating cable (if condensate drain freezes in winter)
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
ComponentComponent Under Test
Expected Range9500–10500 ohms
ConditionIf Open (OL) or infinite, replace component.
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
Part Name
OEM Number
Estimated Price
NTC Temperature Sensor100163938 · $20–$45
100163938
$20 – $45
Condensate Trap100062581 · $15–$40
100062581
$15 – $40
Inlet Filter Screen100113571 · $5–$15
100113571
$5 – $15
Frequently Asked Questions
What is the Code 29 temperature threshold on a Noritz?
Most Noritz units trip Code 29 when the internal sensors hit somewhere north of 160 degrees F on the heat exchanger itself. That's the safety buffer kicking in. If your tap is set to 120 but the metal inside is hitting 180, the system knows the heat isn't moving into the water like it should, and it kills the flame before anything melts. That gap between your tap temp and the internal temp is basically your scale buildup showing up as a number on the display.
Can I keep resetting Code 29 until I get a technician?
Reset it once to see if it was a fluke. If it comes back, stop. Every time you reset it and let it overheat again, you're stressing the thermal fuse a little more. Those fuses don't announce when they're about to go, they just blow, and then you've got a Code 14 and a unit that won't light at all. If you absolutely need hot water short-term, reset it, use it briefly, then let it cool down. Don't run a full laundry cycle on a unit that's throwing a 29.
How is Noritz Code 29 different from Code 14?
Think of Code 29 as the Check Engine light and Code 14 as the engine actually seizing. Code 29 means the computer's detecting too much heat and shutting things down before permanent damage happens. Code 14 means the safety fuse has physically melted and the unit won't run at all until you replace parts. You can fix a 29 with a good cleaning and maybe a cheap sensor. A 14 usually means a parts kit and a couple hours of labor, and on some condensing models it can run close to half the cost of a new unit.
How often should I descale to prevent Code 29?
Depends on your water hardness. If you've got crusty white buildup on your showerheads or faucet aerators, descale every 12 months, no exceptions. If you've got a whole-house water softener running properly, you can probably stretch it to every 2 to 3 years. I've seen units in soft-water areas go four years without a flush and look totally clean inside. But in a hard water area? I pulled a unit last month that was basically solid calcium after 18 months. Skipping descaling is genuinely the number one way people kill their Noritz early.
Can a clogged condensate trap cause Code 29 on a Noritz NRCP?
Absolutely. On the NRCP high-efficiency series, the condensate has to drain out continuously. If the trap gets plugged with mineral gunk or the drain line freezes in winter, that liquid backs up and creates a heat-transfer problem in exactly the wrong spot. The sensors freak out and throw Code 29. Fixed one of these last January in about 15 minutes, just cleared the trap and re-routed the drain line away from the exterior wall. No chemicals, no parts ordered. Homeowner thought the unit was done for.
Do I need a plumber or can I descale my Noritz myself?
Honestly, most homeowners can handle a descale. You need a submersible pump, a bucket, and white vinegar or a proper descaling solution. Noritz sells a flush kit through their dealers too. The part that trips people up is knowing which ports to connect to, so watch a Noritz-specific flush video before you start if you've never done it. But it's not a gas line, there's no real danger here, and the whole job takes maybe 90 minutes. A plumber will charge you 150 to 300 dollars to do exactly the same thing.