Whiff of gas when furnace comes on
I'm hoping someone has an idea of what's going on with my furnace. I have a Trane gas furnace in my home, which serves as the emergency backup to a new Rheem heat pump I had put in over the summer. The furnace is 10 years old, and had been working fine prior to the heat pump installation - just a bit expensive to run.
When winter rolled around, and the furnace started to kick on occasionally when the temperature got too low outside, I started smelling a small whiff of gas coming out of all of most of the registers in my home. It only happens just as the furnace kicks on.
I called the company that installed the heat pump. They came out, looked it all over, bubble soaked the lines, and couldn't find anything wrong. I called another company who came out, removed the burners, inspected the heat exchanger, and suggested that the heat exchanger must be leaking, and charged me $200 for the "diagnosis". They then came back out and replaced the heat exchanger a week later, apparently still under warranty (surprisingly cool of Trane), for another $500 in labor.
Now, every time the furnace kicks on, I get a faint whiff of gas. Same as before, just $700 poorer.
Does anyone have any idea what could be wrong? To repeat the facts:
-New heat exchanger,
-All gas lines bubble-soaked, no obvious leaks
-Only smell gas just when the furnace kicks on.
-Gas smell is coming into the home through the registers, in multiple rooms (strongest in the registers closest to the furnace)
-House was built in 1997, there's no fresh-air intake to the hvac system (closed loop), no obvious air leaks in the ducting around the furnace.
I'm at a loss. Does anyone have any suggestions???
Could be a little bit of delayed ignition allowing the gas to come on for a second or two before ignition. If there is any leakage around the return air on the furnace, could be sucking it in and distributing through the registers. As far as changing a heat exchanger because they think there is a problem and are not sure. I would say the company is nuts. There are certainly ways to tell if a heat exchanger is cracked you don't just replace it on a whim. I would get someone to turn up the tstat and watch what happens when the gas valve opens for ignition. See if it lights right away or takes a few seconds with the gas on. Have seen Trane/American Standard furnaces with a wierd ignition timing. Usually change the board and all is well.
"Go big or Go Home"
I can only guess here. When your heat pump was installed you may have a return air leak now that is pulling by products from the old furnace. You should have it investigated further by the Co you hired to do the work or past Co. Perhaps a 3rd Co.
Get a CO,and gas detector too. Good luck, you still have a problem tho. Not enough info. Get a qualified Co. to check and SOLVE.
never say never
What model of furnace is it?
If it is one of the ones with radiant flame sensing, you could have a problem with the radiant flame sensor, or control board.
One of the more common failure modes with that control setup is that it will power the gas valve as soon as it sends power to the ignitor, without allowing time for the ignitor to warm up.
This causes it to dump gas until the ignitor gets hot enough to light the burners.
I have seen them just sit there dumping gas indefinitely if the ignitor is also failed.
You can tell if it has a radiant flame sensor, it will have a small rectangular black box, about 2"x1.5"x3/4", attached to the same bracket the ignitor is mounted on.
If it is indeed a radiant flame sensing system, it is replaced by a conversion kit to change it over to flame rectification sensing. Includes a control board, flame sensor, wiring harness adapter, a piece for the gas valve, and a few other odds and ends.
The furnace model number, I think, is TDE080A945K0. I'm not sure what the different types of ignition are, or how to identify them. However, when the furnace kicks on, a heating element begins to heat up and glow, near the first burner. 10-15 seconds later, the gas comes on, and is ignited very quickly. There is a slight lag as the fire propogates across to the fourth burner, but it takes less than a second for all 4 burners to ignite.
I'm certainly going to call both companies back out, because it's getting a bit ridiculous. I've just lost faith in the ability of their techs to diagnose the problem, and was hoping someone had some ideas here (so thank you for your suggestions).
I've tried to inspect for any return-air leakage, and I'm not able to find anything significant. There was a small leak just below the furnace (it's downward facing), but it had outflow not inflow. The question I keep trying to answer is, how could gas get into the closed-loop airflow? The obvious culprit would be the heat exchanger, but clearly that's not it. A hole in the return-air above the furnace could pull in gas, if there enough gas leaking out of the furnace to be pulled in in the first place, but I'm not smelling much, or noticing any bubbles when I bubble soak the connections. I really don't have a clue what could be happening. I hate problems that don't make sense.
if there is a lag before the 4th burner lights, that could very well be the gas smell you are getting. the burners are supposed to pass the flame from one to another. sometimes dirt or rust can obstruct the flame from passing smoothly. the burner that is causing a problem can usually be cleaned, but sometimes needs to be replaced depending on its condition.
You say your not smelling much? That means you are smelling something? You shouldn't be smelling gas at all. You still have a leak some where. Doesn't sound like the furnace is the problem, maybe gas is coming from other source near by. Can' t tell without being there, let us know what the pros say when you get them back there.
That particular model is listed as having radiant flame sensor but your observations seem to negate that as a problem, let's see..new heat exchanger, quick ignition, all burners working, no observable return air voids, better look at the venting next, you are out of components..
Class of 70
Regardless of the cause, you need it serviced by a pro ASAP. Whether the fugitive gas is coming from the valve train/ burner or just the normal whiff from the regulator vent, it needs to be inspected and corrected as needed. Too many bad things could be going wrong or about to.
Keep the fire inside the fireplace.
The OP has stated he is going to have involved "pros" return to the scene..He has a new heat exchanger courtesy of the pro in his area, burners were removed and inspected by the pros and he still has a problem and requested some suggestions as to what to have the "pros" check next to eliminate the gas odor..
Class of 70
possibly could be sewage gas from open trap or does the gas line run though the return air platform should be able to find problem with gas leak detector
Is this an 80, or 90% furnnace.
The TDE080A945K is an 80% counterflow furnace, with radiant flame sensing.
Originally Posted by beenthere
I think it is that annoying furnace with the partition in the blower section that makes the blower so hard to get to.
Last edited by mark beiser; 12-15-2007 at 07:27 PM.