Quick answer
Code 57 on a Rheem furnace means the pressure switch is stuck open when it should be closed: the control started the inducer but never got proof of draft. The furnace will not light, which is the safe outcome. Check that the vent termination outside is clear, then cycle the power once. If 57 keeps returning, call a technician to test draft pressure and the inducer.
A Rheem furnace showing code 57 has a pressure switch that is stuck open when it should be closed. That meaning is verified against Rheem's fault chart for the single-stage (-)801 series; on any other Rheem series, confirm it against the label on the furnace door, which outranks a general chart.
The pressure switch is the furnace's proof that exhaust is moving. When the thermostat calls for heat, the inducer fan starts and pulls combustion gases through the heat exchanger toward the vent; that suction closes the switch, and only then does the control allow ignition. Code 57 says the inducer was told to run and the proof never arrived.
Will the furnace run with code 57, and is it safe?
It will not light, and that is by design: no proof of draft, no gas. Rheem's control gives the switch 60 seconds of inducer operation to close. If it does not, the control enters a five-minute soft lockout and then retries. You can hear the pattern from the basement stairs: a small fan runs for a minute, stops, and starts again five minutes later, with no flame in between.
The safety concern is not the code but the temptation to defeat it. A pressure switch that will not close is often telling the truth about a blocked vent, and jumpering it lets the burners fire into a furnace that cannot get rid of its exhaust, carbon monoxide included. Never bypass it.
One safe check: the vent termination, then one power cycle
- Find out how the furnace vents. A condensing furnace has plastic pipes through a side wall; an older mid-efficiency furnace vents up a metal flue or chimney.
- At a side-wall termination, clear snow, ice, leaves and anything leaning against the pipes, and look into the openings for frost build-up or a nest. Our answer on a furnace vent blocked by snow shows how to do it without damaging the pipe.
- With a chimney vent, stay off the roof. Note whether the code started after high wind, heavy snow or roofing work, and pass that on.
- Turn the furnace switch off, wait 30 seconds and turn it back on. Do this once.
If the burners light and stay lit, the blockage was the cause. If 57 is back on the next call for heat, the fault is inside the furnace.
What keeps the pressure switch open, in order of likelihood
- A blocked vent or combustion-air path. Drifted snow and hoarfrost on the termination during a cold snap, a bird or wasp nest in spring, or a sagging section of vent pipe holding water.
- A split, kinked or blocked pressure hose. The small rubber tube between the inducer housing and the switch hardens with heat and cracks, or its port plugs with debris. On a condensing furnace, water backing up from a clogged condensate drain can block that port too.
- A weak or failed inducer. Worn bearings slow the fan until it no longer pulls enough suction; a seized one hums or does nothing at all.
- A faulty pressure switch. The diaphragm stiffens or the contacts fail. It is the part named in the code, but the switch is usually reporting a real problem, which is why it is tested before it is replaced.
How a technician tests draft, and what the fix costs
The test is a measurement, not a guess. A manometer is teed into the pressure hose to read the actual suction the inducer produces, and that number is compared with the rating printed on the switch. Enough suction with an open switch means a bad switch. Too little means working back through the hose, the port, the inducer and the vent until the restriction is found.
- Diagnostic visit: $90–$150, credited toward the repair.
- Pressure switch replacement: $250–$500.
- Draft inducer motor: $400–$900.
- Condensate drain cleaning or a new trap, on a condensing furnace: $150–$350.
Vent pipe repairs are quoted in writing on site, since the price follows the length and route of the pipe. Our glossary entry on the furnace pressure switch explains the part in more detail.
Call when 57 returns after one power cycle with a clear vent. Draft pressure and the inducer need instruments, and work on a gas furnace in Ontario belongs with a TSSA-licensed technician. ZK Mechanical books furnace repair at (647) 801-1252 and through the online contact form; the emergency line runs 24/7. Other Rheem codes, including the overheat fault in code 22, are in the Rheem furnace error code guide.