Furnace is less than 15years old.Its electric pilot with gas heating.The pilot lights alright just cant get the burners to ignite at all times.Sounds like the heater is on all the time. when the burners do light the house gets up to proper temp then shuts down,won't come back on till I shut everything down for a few minutes then restart the furnace. Could tis be a thermastate problem? I have the round dial thermastate with the mercury in it. I would like to go to a pragramable one, would this help?
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Re: get heat for awhile then the furnace shuts down.
Great this is good information. I believe it to be one of two issues. 1) The thermocouple (rod that sticks into the flame) is dirty. You can clean this with some steel wool or light sandpaper. 2) If solution #1 does not work then I will say that we have a faulty gas valve (assuming that the gas content and pressure into the house are ok). These are usually pretty generic and can be purchased at your local Grainger (or the like) supply house. Make sure that you are familiar with all of the components involved and read the directions before you remove the old one. If you are not comfortable with this task PLEASE call a licensed technician over. Thanks and good luck!
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Remove the cover over the burners so an inspection of the heat exchanger is a bit easier. Take an LED flashlight and a small telescoping mirror and inspect the heat exchangers front section above the burners giving special attention to the two sections of the chamber on either side of the pilot light. Many times there will be a hole in the chamber or a crack that will allow the blower that circulates the air into the duct blow out the pilot light.
If you are handy enough, consider turning off the gas and remove the ribbon burners prior to performing your inspection. The pilot assembly is probably attached to one of the burners. Lay them on the floor in the order in which they install in the furnace as some furnaces have dedicated left and right end burners and most older standing pilot furnaces have the one burner with the pilot mounting bracket.
To remove, many times you gently pull backwards towards the gas manifold while raising up on the front of the burners. Once elevated enough, the burner then slips off the brass spud (orifice) and forward and out.
The next reason the pilot can go out is because the safety 'holding' coil in the gas valve is defective. Its responsibility is to hold open electrically a safety circuit proving the pilot gas is burning so that main gas can flow. The thermocouple generates just enough electricity to hold the safety coil open. Coil bad = pilot out.
If your furnace is over 25 years old, there is a good chance there is a hole or crack.
This past week I changed out an old hot air furnace in a rental unit that made me question why the tenant did not go to the owner and offer to pay more rent in exchange for getting the furnace changed out sooner. If you are a renter that is paying the gas bill, then you need to think about this.
The hot air furnace was at least 60 years old. It had been coal fired furnace that was converted to gas many decades ago. The pilot light of this beast was more of a torch than a pilot light. When the thermostat called for heat the flame roared for 15 minutes before the exterior blower unit that was added when the furnace was converted to gas, started up to move air through the furnace and into the house.
As I was starting up the new unit, which took up less than 1/3 of the space of the old beast, the renter came and sat down on the basement steps looking on in amazement. How would that little thing make enough heat for the house? A few minutes later those questions were put to rest very quickly.
After starting the new furnace and burning off the oil that always smokes up the house a bit on a new startup the new little unit had the house warm as toast and was shutting down. Wow, that took less time than the old beast took to just warm up!
The renter related to me how that the old furnace cost over one hundred dollars a month just to run the pilot over the summer months. The wintertime heating bills were many times higher than that. The difference between the bills of the old unit and the bills that will be coming now will be unbelievable. A savings of 40-50% is not at all out of the question.
Now, if you are renting and are paying the bill to feed an old monster of a heating system, I suggest that you make a proposal to your landlord. Offer to pay a bit more rent in exchange for a new heating system. Not only will you decrease your gas bills enough to pay some extra rent and still come out ahead, but you will have the peace of mind that you have a safer heating system under the roof that you also live under.
How many degrees before it reaches desired temp, does it shut off? A thermostat is designed to shut the furnace off a couple/ few degrees before it reaches set temp. It has what is called a heat anticipater, which shuts the burner down, and lets the blower use the remaining heat from the heat exchanger to bring it up to desired temp making it more efficient. If it is more than a few degrees, replace the thermostat. You can jump out the red and white wires to confirm the faulty thermostat. If by doing this, the furnace never shuts down, until you separate the red and white wires. That confirms a faulty thermostat. Hope this helps someone.
The pilot flame heats a thermocouple, so if the pilot goes out, the thermocouple cools and shuts off the gas. It can take anywhere from 20 seconds to 2 minutes for it to shut off. You should hear an audible click when it happens.
Try cleaning the thermocouple tip if you can see ashes or any buildup on it. If you know the wind isn't blowing it out (had mine blow out from high winds before) then I would change the thermocouple before anything else.
A thermocouple is a bi-metallic junction that when heated gives an small electric output. The tip of it sits where the pilot light is ( and it is a copper tube going to the gas valve) and the pilot light heats it up. It creates electricity after it heats up (which is why you have to hold the pilot light knob down when lighting) and opens the gas valve to keep pilot light lit after you let the pilot knob go back up. When it stays lit without having to hold it down, (make sure the thermostat is set low so it doesn't light the burner while you have your hand down there) then you turn the pilot knob to on. It should stay on and you can set the furnace to heat and raise the temperature where you want.
If this is a standing pilot system, turn the gas valve to pilot position. push in the knob & hold while lighting pilot...keeping holding knob down for a minute... this will pick & hold the gas valve. Let go of the knob & see if the pilot stays lit, if it does, then turn the knob to on position & the furnace should start if there is a call for heat from the thermostat
Move the gas valve knob to the PILOT position and press down on the knob. You will be pressing down on a spring loaded safety magnet. Now light the pilot and keep holding down the knob till the thermocouple gets hot enough to produce electrical current and hold that spring loaded magnet in. This is your safety device. If the heat gets too hot the furnace has a fuse in line with that magnet. When the pilot stays lit by itself without you having to hold down the button then advance the knob to the ON position. Then go to the wall thermostat and turn on the heater.
Check the pilot light size. Is it small and not surrounding the top 1/3 of the thermocouple? If it isn't then the pilot orfice is restricted or the pilot tube compression nut could be loose. The pilot gas adjustment screw may also need adjusting if this gas valve has one. These problems should only be addressed by an experienced service tech.