Noritz NR98 & NR111 Code 21
Pressure switch triggered. Noritz restricts this code explicitly: for NC380-SV-ASME and N-1321M-ASME only. If your unit is an NR98, NC199, NR111 or NC250, this number is not on your table at all. The checks are the pressure switch itself, the fan motor, the flue for blockage or obstruction, and abnormal combustion.
Also displayed as: F21
Call a proThe verdict
Call a licensed plumber
A commercial-model code. The pressure switch is what confirms the fan is actually moving air before the burner is allowed to light, so a unit reporting it is refusing to fire rather than failing while running.
Typical cost: $200–$1,200
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 NR98 & NR111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 56), 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.
- Check the flue and air inlet outside for obstruction — Noritz's one cause you can see.
- Confirm your model really is an NC380-SV-ASME or N-1321M-ASME; on any other model in this range the code does not exist.
- Call a licensed professional.
Frequently asked questions
My NR98 is showing 21. What does it mean?
Not what this page describes. Noritz marks code 21 as belonging to the NC380-SV-ASME and N-1321M-ASME only, so on an NR98 it is not a documented code on this table. Check the model number on the rating label before acting — and if it really is an NR98, that is a question for Noritz rather than for a code list.
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 NR98 & NR111 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: