Noritz EZ Series & NCC199CDV Code 21
Burner chamber high limit switch triggered. The second high limit switch — the one in the burner chamber — has tripped. Noritz checks whether it triggered, whether it is properly connected, and whether the burner chamber is clogged or damaged. The remark is the important part: to reset this error code, contact the nearest Noritz agent. Unlike code 20, cycling the power will not clear it.
Also displayed as: F21
Call a proThe verdict
Call a licensed plumber
A locked-out safety switch in the burner chamber, with a damaged or clogged burner chamber on Noritz's own list of causes. There is no homeowner reset and there should not be — this is the appliance refusing to burn gas until someone qualified has looked inside it.
Typical cost: $250–$1,500
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the EZ Series & NCC199CDV — not averaged across the brand.
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Leave the unit off. Cycling the power does not clear this one.
- Call a licensed professional or a Noritz agent — Noritz requires an agent to reset this code.
Frequently asked questions
What is the difference between code 20 and code 21 on this unit?
Two different switches in two different places. Code 20 is on the primary heat exchanger, is commonly caused by scale, and clears with a power cycle. Code 21 is in the burner chamber, has a clogged or damaged burner chamber among its causes, and Noritz will not let you reset it at all. Twenty-one is the more serious of the two by some distance.
Code 21 on other Noritz series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
Don't confuse this with
One other Noritz EZ Series & NCC199CDV code points at a switch too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: