this is for my house furnace. It just started doing this the last couple of days. It will run fine for a day or so,then it will shut off and not start back up. If I turn it off and on by the thermostat control,it will sound like it is going to start for about 30 seconds,then shut off again without kicking on. no matter how many times I try to start it,it will not start up. then it will start up several hours later and run fine for a day or so before it craps out again. It did this 2 years ago,and I had to call a service guy to come fix it. I would really like to fix it myself this time and save $150. I have no experience with HVAC repair.This is a natural gas,auto pilot furnace. Is this doable by someone with no experience,and where would I get the parts from? thanks for any advive....Ben

 

Try cleaning the ignitor. It looks similar to the ignitor on a propane grill. Light sandpapering should clean it up. You may have to adjust the gap too. If the pilot isn't firing up, your furnace may shut off due to ignition failure. It'll have to restart the purge cycle, which may take around 5 minutes.

Sometimes the pressure switch goes goofy - pull it out and see if there is any dust or grit in it. It might say 'Dwyer' on it, or have a pressure rating in "W.C. (inches of water column).

The cost of an HVAC service call might not be nearly as bad as a cleanup for frozen pipes. Good luck.

 

I think I would leave the furnace to the professionals. Trying to do this your self could cause more problems an the longer you dont have heat the colder its getting. BTW how old isthe furnace?

 

First the advice- With something as critical as a furncae, I am willing to spend the $$ for someone to professionally fix it. There is just way too many things that can go wrong with extremely bad results.

This sounds like a problem I had with a furnace in an apartment I was renting a few years back. The furnace would go through the warm-up cycle... you could hear the gas jets kick on, the blower just wouldn't start... then the whole thing would shut down. Whenever I would complain about it, the apartment complex's repairman would come by, kick the thermostat all the way to 90* and it would start with no problem... it just wouldn't start up at the 68* I had it set at. I finally gave up and called a furnace repairman. He said that what I had was actually a pretty common problem considering the age of the furnace and from dealing with similar instances in the same complex. There is a temperature sensor that tells the furnace blower that the heating fins are warm enough & to start the blower. In my case the sensor had been coated by years of neglect, dust & carbon. The furnace guy told me to pull out the sensor and clean it with steel wool (made the brass nice & shiny). When I tried the furnace again, it ran perfectly.

Call some HVAC repair companies and see if they can give you a best-guess over the phone. But when in doubt, call the professionals. Don't be afraid to ask questions!

 

Shut your furnace and outdoor AC unit off at the breaker. Take the cover off your furnace, and look for corrosion around the wire connections. Tug on wire going into connectors, especially the t-stat wires, they are single strand 18 gauge and often break where they are nicked by improper stripping. Screw type wire terminals, back the screw off 1/4 turn and retighten. Take any wire nuts apart (one at a time!!) and look under them. replace any that look bad, if the wire is bad shorten and restrip it, reconnect with a new wire nut. I like to put a wire tie under the wire nut over the wire insulation, to stop the wire from twisting back out of the wire nut. Also try and point the wire nut up so it doesn't trap dirt and moisture. If there are plug in type wire terminals on the gas valve, wiggle them to make sure they are tight. If you need to replace any, only do one at a time! and cover any unused terminals so you won't accidently plug into the wrong connection. Next thing to check is the on-off switch at the furnace or at the top of the steps, replace if in doubt with a HD 20 amp switch Two pole single throw if furnace is 208-230volt. On Lennox's, the in the cover circuit breakers are famous for sweating in the summer and corroding. Look at them carefully with a strong light and magnifing mirror, replace if there is the slightest sign of them getting wet. When you are done turn both the breakers back on. Even though you won't be using the Outdoor unit till spring, there is a heater on the compressor, to keep it from flooding with refrigerant, that needs to be on. Also I noticed you are from the Midwest, some localities require a Hi-temp switch on the duct work. Look for a wire coming out of the furnace (it may be run inside the duct work) and to the top of the duct to a retangular grey box or to something the looks like a domed disposible coffee cup cover, repace if over 10 years old. PS this wiil be within 3 foot of your furnace.

 

thanks for the info guys. the furnace is 5 years old. looks like a repair call is in order,I just didn't want to call them when it is working good,and they pretend they fix something,charge me the repair bill,and I have the same problem again in a couple days again

 

Ben, most companies will come back for free if it breaks less than a week later. If they won't then tell them not to bother, you'll find someone that cares about their customers.

 

"Thermistor," I think the dang thing is called. Replaced three of them in the old house over 15 years, about $150/pop. Tell me again why the old-style furnaces with a pilot light were so bad?

 

They could fill the house with gas if the wind coming in the flue was stong enough to put out the pilot light. Also they were known to release a small amount of CO. That anyone with a brain knows went right up the chimney, but alas some rocket surgeon (LOL!!) thought that it was a problem anyways.

 

COuld be one of the hihg-temp cutoff sensors. Depends on the furnace. Mysons did this and I found three different HT-sensors. If one of them triggers, it shuts of the gas flow and won't continue to run or start. If one goes bad, then it won't start. I just took a jumper wire and bypassed each sensor adn was able to id the faulty one. One you bypass the bad one, the furnace will fire right up. Left it bypassed (the other two wroked fine, went to an appliance store that carried stoves, furnaces, etc adn ordered a new senosr for about $12. A lot cheaper than the $150 service call plus parts! put it in and plugged it back up and its worked fine since then.

Had the same thing happen on a close dryer that quit heating, only blew cold air. The high-temp, overheating sensor had goen bad. Cheap easy fix.

 

My guess would be the high limit swicth or the pressure switch. I had the same problem with my gaspack (Trane). It turned out to be the pressure switch. I had the same thing going on with mine, that you describe about yours. Unit would come on and and exhaust fan would kick on for a few seconds then shut off, all the while the blower was running, blowing cold air into the house.

 

If it's going through the purge cycle (induced draft fan discharges to the chimney, running for ~30 seconds), then the ignitor operates and lights the burner, but the burner goes out after about 10-30 seconds (blower may or may not start depending on how long the bruner was fired), I'd be next looking at the flame sensor. These can build up a coating over time, such coating inhibits operation of the sensor and the control unit thinks there is no flame, thus shutting off the gas. The process repeats and repeats, and the burner will not stay fired and produce heat.

The flame sensor will have what appears to look like a rod that is actually in the flame. There should be one wire leading to it. They take about 10 minutes to remove and clean with a scotch-brite.

 

If there is a flame sensor, try replacing it - they work by "grounding" thru the moisture in the flame - they have to be well insulated, and a very small carbon track, or dirt, whatever can reduce the resistance enough to screw things up. There are a number of other "sensors" also, depending on the type of furnace - hi-efficiency or other. There are sometimes more than one pressure sensor, overtemp cutouts, etc. Some have infrared sensors for flame detection....Best bet is to acquire a knowledgable friend ......

 

Flame sensor - that's what I meant to say. Clean it and adjust it so it's in the hottest part of the pilot flame.

 

alchymist has the ultimate solution if the falme sensor proves bad; reliability is critical at this time of the year. Two nights ago and at 11pm my neighbor called me moaning about his furnace not working consistently. This call could have been done for two days. The problem? A dirty flame sensor. My suggestion, given this has happened 2X in 6 years, clean it for now but replace it very soon. His solution, that costs money so cleaning is great . Oh well, he was generous with the Crown Royal that light .