Ignitors shutting of for about 30 sec then relighting.
Lets say the thermostat is set at 70 degrees and it is 67 degrees in the house. The furnace will come on and stay on for several minutes. Then the flame will go out for about 30 seconds and re-lite. All this happens before reaching the 70 degree set point. The blower motor stays on until it relites and reaches the set point temp. I have changed the air filter. The motor blower vaines seems to be in good shape. I have not cleaned the coil yet due to the location. Hard to get to, however the is a spot that I can see some part of the coil and it doesn't seem to be dirty. It has a 4 way limit switch on it that could be suspect. The furnace was installed in 1987 and it is an Amana. Thanks for your help..
This sounds like a flame sensor problem. You may lightly sand the sensor for a better sensing the flame that will keep it running. There is another problem it could be. Check that the proper gas pressure according to the mfg is correct. A very slight amount has cause this problem quite a few times. You should have a qualified person with a gauge designed for this to test it. Maybe you could get your local gas provider test the gas to the home 1st. The gas pressure adjustment and test should definately be preformed by a qualified tech. Good luck J
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Some thermostats have a swing setting that can be adjusted. A swing is the setting when you want the furnace to stop or start from the desired set point. For example, you set your thermostat at 70 and the swing is set at 10 degrees. Then the furnace will turn on 5 degrees below 70 and shut off 5 degrees above 70. Check you thermostats manual if it has this option.
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.
Try this simple test Turn the thermostat down to room temperature If it turns off when you reach room temperature it means the thermostat is ok Now if you place the thermostat back to 82 as you say you must have to leave it there until the warmth returns to the furnace thermostat So it's either bloody cold were you are or your furnace is undersized
Does the furnace stays off?.
Furnace are ment to cycle on and off because of limits .If you set to 70 furnace would cycle several times before reaching that temperature.
Just make sure your filters are clean and you got proper return air flow because lack of air flow will cause furnace to shut off sooner than normal
Since it's within 2 degrees of your setting it could be one of two things. Most furnaces run longer (pass your setting) to maintain the setting you made. Which really not a problem. However, your thermostat may need calibrating. To test this theory, place a regular wall thermometer next to your furnace's thermostat and see if the two temps match when the furnace cuts on and then when it cuts off. If the temps are both the same, the furnace thermostat is fine.
If you're turning it down to 68, because no one will be at home during the day, just set it 2 degrees cooler than 68 degrees. You will then wind up with 68 degrees.
You didn't include a model number, so it's hard to know for sure - but I'll take a stab at this one. Many of these t-stats have a programmable offset to reduce "hunting". This can be as little as 1 degree or more than 2 degrees.
This means if you set the offset to 1 degree and the room temperature to about 65 degrees, the furnace will heat the room until the t-stat registers a rising temperature of 66 degrees. The furnace shuts off and will not turn on again until the t-stat registers a falling temperature of 64 degrees. The average is 65 degrees, and prevents the furnace from starting and stopping numerous times instead of just once with the 1 degree offset.
You can further reduce the number of furnace start and stops by increasing the offset to 2 degrees. This would work like this when the t-stat is set to 65 degrees and the room is cool:
Room Temp Furnace 63 On 64 On 65On 66 On 67 On 68 Off
The room is now warm and heat or furnace is off. The room begins to cool like below:
67 Off 66 Off 65 Off 64 Off 63 Off 62 On
With a 1 degree offset, the room temperature varies +/-1 degree (about 2 degrees total). With a 2 degree offset, the temperature about varies +/ -2 degrees (about 4 degrees total).
Also, when the thermostat shut the heat off, the heat that was made is delivered to the space instead of wasted by sending outdoors - so the room will get a little warmer even though no fuel is being burned. The same holds true at the other end. When the t-stat turn heat on, fuel is burned, but there's little heat until the source has reached the optimum temperature and then the heat is delivered to the space.
I hope this helps & good luck! Pleas rate my reply - thanks!
If your heat anticipator in the thermostat is bad or set at the wrong amperage, it could do just as you describe. If the air filter is dirty or the ducts are restricted, the furnace could shut down on high limit. I would check the air filter and replace if necessary. Make sure all registers are fully open and last, change the thermostat.
When the thermostat calls for heat it should run until the room reaches the temperature setting then shut off. Is the blower motor running and can you feel air coming out of the vents? It sounds like the blower is either not running or putting out enough air to keep the furnace heating. The blower moves the heat from the heat exchanger to the room, if it can't remove enough heat from the heat exchanger there is a limit switch that will shut the burner off if it gets to hot and that's what it sounds like is happening.