In extreme cold, your furnace and hot water tank vents can ice up, causing the appliance to fail. Try these steps before calling a technician to your home.
Locate Exhaust and Intake
Look at the furnace or water heater and find the intake and exhaust pipes. They are usually white plastic pipes, but they may also be black. Find where they exit the building, most likely through a wall near the appliance.
Find the intake and exhaust pipes outside, based on where they exited the building. You should find the pipes near the foundation of the home, however some systems have them piped to the roof, in which case a ladder will be required to examine them.
Look closely at the intake and exhaust checking for anything that could block the pipe.
Remove any ice or frost completely. Even a small amount can cause a furnace to fail. Check the insides of the pipes as well.
Check for Ignition
If the blockage was indeed the problem, the appliance could start up again automatically. In most cases you may have to cycle the power to the unit. Check the start-up instructions in the manual. if it doesn’t work after restarting, there may be something else at fault.