Have HVAC Questions? Ask an HVAC Expert for Answers
What is the brand and model number of your furnace?
There should be a rating tag inside the burner compartment. Look there
Ok, a 4 blink code is an open limit circuit. The easiest thing is to try resetting the roll out out switch(es) (see attached pic for typical). They are located just outside the burner chamber. Turn the power off to the unit then try pushing the small button between the 2 leads on the switch. If it clicks you have reset it and the unit will fire up when you turn the power back on with any luck. If it doesn't click it wasn't tripped
Then you either have a bad limit (the furnace should have cooled down by now) or a bad connection in the limit circuit. You can try checking all the connections on the limit circuit. That would be the wire the rollouts are connected to
The main limit is on it's own circuit on this model. Red wire. The limit is a rectangular "patch" with 2 terminals located above the burners where it can be inserted into the heat exchnger
Like I said before the main limit on this model is on a different circuit that the rollouts, it has a red wire. You need a continuity tester to check these devices
You can't run the furnace with it jumped out but you could test it. If the furnace doesn't lockout then the limit is probably bad since the furnace must be cold by now or if it locks out after running for a while you could have an air flow problem from a clogged AC coil or a dirty filter.