Suburban SF and NT series fault codes
The 3 fault codes below are the ones that apply to this Suburban furnace family. The other 1 Suburban furnace codes in our database belong to different model families — they are listed further down so you do not troubleshoot against the wrong table.
Covered model numbers
NT-12SNT-16SNT-20SSF-20FSF-25FSF-30FSF-35FSF-42F
Not on the list? Check the rating label before you troubleshoot — the code table below will not apply. Where to find it →
Fault codes on the Suburban SF and NT series
The high-temperature limit switch is a normally-closed safety in series with the ignition … Low-voltage standby info
The Fan Control module board continuously monitors supply voltage. On the 12 VDC board it … Sail switch lockout warning
On the 12 VDC Fan Control module board, after the thermostat calls for heat the board firs…
Codes that do not apply to this model
These 1 codes exist on other Suburban furnaces. If your unit is showing one of them, it is not from this family — re-check the model number on the label before acting on any of these.
Where the model number is
On the furnace casing itself, reachable through the return-air grille or the exterior access door, not on the thermostat.
Sources
- Suburban Furnace Service & Training Manual (SF 20/25/30/35/42 series) — Suburban Manufacturing Company (Sequence of Operation for 12 VDC Fan Control Module Board — sail switch verification / 30-second lockout)
- Suburban DYNATRAIL Furnaces NT-Series Service Manual — Suburban Manufacturing Company (Sequence of Normal Operation & Service Hints C (Blower Runs but Burner Does Not Light — sail/micro switch))
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