gas furnace question?

Question

I have a gas furnance with forced air fan; about 5 years now ; the burner fires up ; all tubes light but then go off; fan is on; tries to recycle again , fires up and then gas shuts off again; and again and so on ; works sometimes but more often does this off /on cycle; Gas company came our (twice) said that it is sensitive to dust; I have dusted that thing like crazy; he took it apart, couldn't find anything; again sometimes works sometimes not; we are on a slab so it is in a closet with vented doors; I took one door off to prevent a circulation problem ; still the same. any suggestions;

it can't be overheat problem b/c the burners just fire up and then shut off

Answer 1

Here is your answer! When the burners ignite the flame must be sensed by a 'flame sensor. Look at the area where the hot surface or spark ignitor is located. Most likely hot surface. Now go to the burner tube farthest from the ignitor. At that tube near the area where the flame comes out, you will find a metal rod about 2 inches long that is bent in a 90 degree shape. This is the sensor. Using a 1/4 inch nut drive or socket wrenceh, remove the flame sensor. Sometime lightly sanding this with abrasive cloth or steel wool will correct the problem. Reinstall and start the furnace. If it still has the problem, go to and air conditioning and heating distributor (Johnson Supply, Acr supply, Johnstone supply) with the part, model and serial of the furnace, and get them to match you up with a replacement sensor. U R Fixt!

Answer 2

I can't decipher how long the burners are running from this. Usually if the fan keeps blowing we know the thermostat is calling for heat. So the burners light. But there is a safety switch that shuts off the burners if the system gets too hot.

Since the thermostat is still calling for heat, the fan runs and cools the system, switch resets and the burners fire again - as a cycle. Usually this is caused by a really dirty air filter, which isn't allowing enough air to take the heat away from the system and disperse it into the room.

Check your filter, replace if really dirty. Also check for obstructions on your air intakes, or maybe is someone closed off too many of the output vents.

This can all be checked by you for free.

Answer 3

There is a gas regulator valve in the gas line before it gets to the furnace, and this is mounted usually right on the front and has the knobs used to turn and depress when you have to re-light the pilot. There is a filter in this valve and sometimes the filter gets dirty and will cause symptoms like you describe. There are also delicate parts in this valve and the microscopic grit that flows in with the gas will cause wear on these parts and that can be a problem too. Probably the valve should be replaced, although I cannot see why the service tech from the gas company did not do this already. I have had the same sort of thing happen on my furnace.

Answer 4

It sounds like a topic with the flame sensor being grimy or the administration board could desire to be going undesirable. count quantity the blinks of the crimson easy and then verify out the chart on the get entry to door and it will assist you narrow the subject down. For a step by skill of step troubleshooting instruction manual, look on the furnace internet site at my source.