It’s almost time for the furnace to take a hiatus and for your air conditioner to be called up from the ranks. That means it’s also time to let your furnace rest, knowing that it will be ready to go when the cold weather sets in — which will be sooner than you think. Before you shut your furnace down for the summer, it is important to have someone maintain it, or to maintain it yourself, so that come cold weather you don’t have a real problem and expense on your hands.
12 checklist items
1 Check the flame sensor
To check your flame sensor, you need to hook up a multimeter to the sensor wire alongside the flame sensor, and then start the furnace on the “heat” cycle. The readings you should receive are somewhere between 1.5 and 4 uA, according to the manufacturer’s specifications. Readings less than 1.5 could signal a problem with your flame sensor that could lead to its malfunction.
2 Check the ignitor
To check the ignitor, you have to measure the total resistance that runs through it. If your furnace installation has a silicon nitride ignitor, the sensor should read anywhere from 11-17 ohms. If your furnace has a carbide ignitor, then the readings should be from 50 to 100. If the measurement is anywhere outside of those ranges, then you should consider replacing the ignitor. Just remember to test when the furnace is cold, not hot.
3 Pull out and clean burners
One of the biggest reasons that a furnace will malfunction is due to the burners. Burners can become maligned or contaminated, which can stop them from burning correctly. Anything that disrupts them could stop the flow of either air or gas, both of which are needed. A stiff brush is enough to clean the burners if you notice any debris. It will also ensure that you aren’t subjecting yourself to a potential carbon monoxide leak.
4 Check the heat exchange
You will want to visually inspect the heat exchange to ensure that there aren’t any holes, cracks, or rust building up.
5 Blow out the condensate line
Try to blow out or remove the P-trap to remove any debris or pressure in the condensate line. This is a problem with over 90% of furnaces and can lead to a pressure switch lockout. If you clear the lines, you don’t ever have to worry about making a costly repair call for no reason.
6 Check the pressure of the static system
First, determine if you have a non-variable speed or a variable speed motor. If you have a non- variable speed motor, then the internal pressure should be .50-in wc; for a variable speed the read should be .80-in wc. While you’re checking the system, make sure to refer to the fan chart on your furnace to be sure that you are reading the right number.
7 Do a combustion analysis
Fire up your combustion analyzer — but only while you are outside your home to get the proper calibration. Since it involves CO emissions, you will want to make sure that you are outside while testing. If the calibration is off, then you definitely want to make a service call. Operating CO levels should remain between zero and 99 ppm to maintain stability.
8 Record temperatures of the supply and return plenums
For your furnace to be running appropriately, you want the air plenum on the condensing temperature and the induced-draft furnace to be a minimum of 60 degrees warmer than the temperature of the air. Your flue temperature should read over 170 degrees more than the supply air plenum, and the condensation should be greater or equal to the air plenum temp.
9 If necessary adjust the gas pressure
Check the manufacturer’s guide to ensure that the gas pressure is appropriate; if not then make the necessary adjustments to avoid danger.
10 Inspect for gas leaks
Use the water and soap method to check for any leaks.
11 Make sure the vent pipe is properly supported
On condensing furnace systems, sometimes the water condensation will pool when it is venting. Make sure that the condensate pipes aren’t adding additional pressure, and if they are, drain them by making small cuts and then fusing the pieces back together for more efficient energy flow.
12 Check the heat-off system
To ensure that you are getting the maximum efficiency from your unit, try to set off the heat delay system to make sure it is working appropriately.
You don’t need to be an expert to know when you need to call one. These 12 simple musts to check your furnace will ensure that when the fall comes around, your furnace will be working in tip-top shape.