Noritz NR50, NR66 & NR71 Code 20
High limit switch triggered. The high limit switch has tripped. Noritz's checks are whether the switch is triggered and whether it is improperly connected, and the power has to be cycled to clear the code. Four flashes on an NR71 or N-0631S with no remote controller.
Also displayed as: 4 flashes
Call a proThe verdict
Call a licensed plumber
Cycling the power clears it. If it returns, the switch is doing its job and something upstream is genuinely overheating — scale, restricted flow, or overfiring.
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 NR50, NR66 & NR71 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 54), 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.
- Check the water filters are not restricting flow.
- If it returns, call a licensed professional. Never bypass or jumper a high limit switch.
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: