I read your post and wanted to ask for your help. I have a Carrier 58 RAV, restarted it, tripped all the limit swithcs, sanded the flame sensor, and then noticed a LED is flashing three short and one long, indicating a code 31 i learned from your post, but looking at an online manual,
I couldn't find a pressure switch. is it in the control valve?
The pros in my area is overwhelmed with new construction work, and told me 6 to 12 weeks to get out to my place, which is out of town a long way.
I am very comfortable with plumbing and wiring.
I hate to bother you with this, but it is still cold some nights here in Colorado.
Thanks in advance
Originally Posted by HVACDave
To determine if it is code 13 or 31. The first digit is the number of short flashes, the second digit is the number of long flashes.
13 is limit circuit lockout, in which case your furnace would try and restart after 3 hours. The limit circuit is there to protect the furnace from overheating if there is insufficient airflow through the heat exchanger taking the heat away from the furnace and pushing it into your ductwork. If this is the code then look for plugged air filters, blocked discharge vents, etc.
31 is the pressure switch didn't close or reopened. This pressure switch is in your furnace to monitor the combustion fan motor to prove you have positive exhaust gas pressure out your exhaust vent and through your combustion chamber. This could be triggered due to plugged intake and/or exhaust piping, defective exhaust blower fan, excessive wind, plugged tubing on the pressure switch, etc. These pressure switches are very sensitive, do not take the hoses off and blow into the switch or you will damage it. I have also seen where an improper grade on the furnace will cause this fault. It should have a slope of about an 1/8 th of an inch from the back to the front of the unit, if not you may build up condensate in the secondary heat exchanger and not get enough flow through the ventor motor.
both of these conditions can be reset by turning off the power to your furnace and then turning it back on. The furnace will then go through its normal start up procedure.
Have a look at your vents outside and make sure that there haven't been any birds taking up residence in your vent pipes, also check your condensate drain ine to make sure it isn't plugged.
good luck, if in doubt get it checked out by a pro, this isn't a trade you want to mess with if you aren't comfortable with it.