Troubleshooting tips for gas furnaces and boilers

July 27, 2015

While gas furnaces and boilers are relatively trouble-free, things can go wrong. These troublingshooting tips can help you spot and fix the problem.

Troubleshooting tips for gas furnaces and boilers

Always start with the pilot light

  • Some newer gas furnaces have an electronic igniter that lights the pilot light or the burners directly. If it fails, have it serviced.
  • Many units have a pilot light that stays on all the time. If it goes out, the burners cannot be lit.
  • Controls vary from model to model, but instructions for relighting the pilot light are almost always on a label near the control valve.  Follow them carefully.

Changing a thermocouple

This is a very common repair and a hardware store or home centre will have the part you need. Getting a service professional  usually ends up being expensive, but you can install one yourself for a few dollars, if you're willing to get a little dirty. Here's how:

  1. Turn off the gas knob and shut off electrical power to the burner, and wait 10 minutes for any gas to dissipate.
  2. Use a flashlight to locate the thermocouple. It's a copper tube with fittings at each end.
  3. Using pliers or a small wrench, unscrew one end from the control valve, and unscrew the nut that holds the other end to a bracket.
  4. Carefully note where the new thermocouple will need to go.
  5. Take the old thermocouple with you to buy a replacement of the same size.
  6. Bend the tube carefully as you position it and tighten the nuts on each end.
  7. Relight the pilot.

Getting the perfect flame

  • You can adjust the air intake by moving a plate or sleeve over an opening on the front end of each burner.
  • To tell if this air shutter needs adjusting, look at the flame. A harsh blue flame needs less air, and a weak blue inner flame with a yellowish needs more air.
  • A well-balanced flame has a distinct blue-green inner flame and an orange outer flame. The colour may differ with bottled gas.
  • To adjust the air intake, loosen the screw on the air shutter and gradually move the sleeve to allow less or more air to enter.
  • Newer burners with fixed shutters rarely need adjustment. If they do, hire a pro.

Scrubbing the pilot opening

  • If your pilot light goes out and won't light, the opening may be clogged.
  • Close the gas shutoff valve and shut off electrical power to the burner.
  • Remove the access panel. To reach the pilot, you may need to remove the bracket holding it and pull it out a bit.
  • Use a toothpick to clean out the opening. Work carefully, so you don't break the toothpick in the opening.
  • Use a soft brush or a cotton swab to clean the area around the opening.

Clean burners for the right flame

  • To operate efficiently, the small holes in the burner must be clear of dirt.
  • Clean them at the beginning of every heating season.
  • Remove the panel or panels to get to the burners.
  • Vacuum around each burner. Use a brush to loosen dirt as you vacuum.

Even though gas furnaces and boilers are very reliable, things can still go wrong. If you start by checking the pilot light and other common problem spots, you could know exactly what to do next.

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