Category Archives: Heating

Furnace has power , but no activity

Does your furnace have an inspection window in the fan door? Typically this is a 2″ diameter piece of clear plastic on the face of the fan door or it could be in the burner compartment. If you look there should be an LED light of some sort. It could be a steady red light , pulsing light with slow or fast pulses or it could be flashing a code. 1-10 pulses and then pause. This code will match up to a trouble shooting chart which will tell you what the fault is.

For a typical furnace control board , these will indicate things such as an open limit , open air proving switch, faulty processor or active time delay. You need the chart from the manufacturer. Look on the furnace labels or search online.

Is the LED light off and the system is powered? This could mean the board has failed or the 24 volt control transformer has failed. There is usually a fuse or breaker on the transformer or circuit board. A short in the thermostat or other control will shutoff the transformer or burn it up. Can you smell any burnt odors? Compressor contactors often cause this issue.

If you reset the transformer and it trips right away , it a dead short. Does it trip during the start-up of the burner or when the fan switches on? It can give a clue as to what is causing the short.

Next try to turn of the power to the furnace. Wait 1 minute and turn it back on. This should reset any ignition safety or time delays. If this works to get the heat on and does not trip again in the next month , then its likely ok. If it continues to locks out , then call for help. It needs to be inspected and may not be safe to use.

Combustion fan starts but fails to light