Noritz NCC199 & NRC111 Code 20
High limit switch triggered. A high limit switch has tripped. Two details make this entry different from the same number on other Noritz ranges. Noritz prints a note against it — this model has two kinds of high limit switch — so which one tripped is itself part of the diagnosis. And the third check is whether the exhaust gas temperature is too high, which pulls the flue into a code that elsewhere is purely about water.
Also displayed as: F20
Call a proThe verdict
Call a licensed plumber
Cycling the power clears it. If it comes back, the switch is doing its job and something upstream is genuinely overheating. Noritz putting exhaust temperature on this checklist means it is not safe to assume it is only a water-flow problem.
Typical cost: $150–$900
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 NCC199 & NRC111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 55), 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.
- Note how quickly it returns after a power cycle — a fast repeat and a slow one point at different causes.
- Check the water filters are not restricting flow.
- Note when the heat exchanger was last flushed.
- If it returns, call a licensed professional. Never bypass or jumper a high limit switch.
Frequently asked questions
Which of the two high limit switches is mine?
Noritz does not say on this page — it only records that the model has two kinds, which is why the technician needs to identify which one opened before deciding anything. Mention the note when you book; it saves them finding it out on your time.
Code 20 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: