Universal diagnostic library
Furnace problems and diagnostic-light interpretation
Furnace problems and diagnostic-light interpretation: record the operating sequence and status code before power cycling. Furnace codes are listed by manufacturer, each taken from that manufacturer's own literature. Furnace codes are listed by manufacturer, each taken from that manufacturer's own literature.
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5 complete records in this directoryHow to read a blinking light on a Trane furnace
Trane's own page says a furnace light's meaning depends on make and model and publishes no code table. Here is what Trane does say, what to record, and what the S9V2 control's fault menu shows.
Open record Carrier furnace · indicatorHow to read a Carrier furnace status-light code
Carrier's own guide explains the amber status light on its variable-speed furnaces: continuous on, off, rapid flashing, and the two-digit codes where short flashes are the first digit and long flashes the second.
Open record Furnaces · lockoutFurnace lockout: hard lockout, soft lockout and what resets it
What a furnace lockout is, the difference between a soft and hard lockout per Trane, how long Carrier and Lennox lockouts last before the control retries, and the only fix Trane says to try yourself.
Open record Furnaces · no heatFurnace runs or calls for heat but the house stays cold
Work a gas furnace that will not heat in the order Trane and Carrier use: thermostat, power, filter and airflow, gas supply, then the status light. Includes where the Carrier and Lennox code lists are and when to stop.
Open record Furnaces · cyclingFurnace starts and stops every few minutes
Trane says a normal furnace cycle lasts at least 7 minutes. Find out whether yours is short cycling, the most common causes in Trane's order, and which ones are safe to check yourself.
Open recordFurnace problems and how to read the status light
A furnace that has shut itself down is usually protecting you, and its status light tells you why. The light flashes a code on the control board, and the legend is printed inside the access panel: Trane, Carrier, Lennox and others each use their own sequences, so match the legend to your furnace, count the flashes and write the code down before you restart it. Many codes concern the pressure switch, which proves the exhaust is venting, the flame sensor and the limit switch.
A furnace that runs but does not heat the house may have a dirty filter, a closed vent or a thermostat problem. One that starts and stops every few minutes is often overheating from airflow or failing a safety check. Furnace lockout, where the control stops trying after repeated failed starts, can be reset at the thermostat or power switch once. Never bypass a safety switch, and call a licensed technician for gas, burner and inducer faults.
What is furnace lockout?
The control board has stopped trying to start after repeated failures, to protect the system. Reset it once, and if it locks out again call a technician.
Why does my furnace start and stop every few minutes?
Restricted airflow from a dirty filter or closed vents is the usual cause, or a safety switch that cannot prove airflow or flame.