How to Troubleshoot Your Furnace (Throw Money At It Seriously)

[Jeremy Tillotson]

Ok everyone I thought the title was funny. I was reading a post about a furnace tonight. I am a licensed HVAC guy (although a full time investor) and thought with the cold spell I might help some people with the furnace isn't working. 

On any furnace that is 90% efficiency (it has a white pvc vent pipe) there will be something called a flame sensor, These can be cleaned by using a dollar bill. Take the bill and slide it over the rod slide it back and forth and it will get rid of the white film that over builds up this part. So just throw money at it to fix it, lol I posted a photo of a frequent setup as to how this looks its a little rod. They do vary and some are at a 90 degree angle.

Picture of a flame sensor

I will go more in depth here. First thing I do when I get a no heat call (besides make sure tenant didn't get gas shut off), is to check the t-stat. Is it on heat and set. If it has a fan switch turn it to on does the fan come on? If not change the batteries on t-stat and try again.

If it doesn't you need to check for power to furnace, and if that doesn't work you can check the doors on the furnace to see if they are tight and the door switch is engaged.

A normal sequence of operation would be the induction motor comes on, after a few seconds, it will check whats called a sail switch to ensure it is venting air, at that time the glow plug should come on, and following the gas valve opens, firing the burners, the flame sensor will check to ensure that the flame did light to ensure burners light, and then the blower motor will engage. 

I hope this helps everyone

Disclaimer: This article is meant for those who feel they have the skills to diagnosis the problem and if you feel its more than you can handle you should call a professional. This still may help one in knowing what kind of problem there is so that don't get ripped off.

[Don Harris]

@Jeremy Tillotson , thanks for sharing. 

[Steven J.]

Stupid simple tip. I like it!

[Steve Babiak]

Two other silly free fixes. Emergency switch bumped out of the ON position; make sure it is really ON. On those direct vented high efficiency systems, the air intake pipe can be blocked by trash flying around outdoors on a windy day; the air intake sucks outdoor air, and those plastic grocery bags flying around are ideal for blocking that air flow. 

And somebody could just place such an obstruction to be evil ... in neighborhoods where owner occupants hate renters ...