We had a call in Ravenswood where the customer told me that the high limit safety was going off on the furnace. The customer explained that they replaced the limit before and that the circuit board diagnostic is still flashing the code that said there was a limit fault.

The customer had read a bit online about troubleshooting and knew a little about the subject and was willing to walk through a couple of steps over the phone to resolve the problem. I’ve listed here a couple of possible issues a furnace can have if the circuit board is giving you a code for high limit failure:

Clogged Air Filter. Change your air filter every month for better air quality, energy efficiency and better home heating.

Obstruction in the Evaporator Coil: You either need an inspection camera or to physically take apart the sheet metal plenum to see if the evaporator coil is clogged. This is not the easiest way to do it, but it works.

Heat Exchanger Issues: When there is a crack in the heat exchanger the roll out limits will open and need to be manually reset, this is very common and a tell tale sign of a cracked heat exchanger and needs to be replaced.

We are happy to answer any questions that you may have, please contact us anytime if you live in Ravenswood for any heating repair issues at 773-219-1102.