Trane XL 80 furnace "choking" on high setting


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Old 10-06-11, 11:21 AM
K
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Trane XL 80 furnace "choking" on high setting

Hi all, newbie homeowner and newbie on this forum here. I have a 15 year-old Trane XL 80 gas furnace and I had it serviced a few months ago. The service seemed quite comprehensive, and the technician said it's still in good condition except for some "inducer corrision".

However, the duct cleaner came yesterday and commented that my blower compartment was caked in dust and he said most likely the blower motor is similarly clogged - I started questioning the servicing was not as comprehensive as I thought.

As it is cooling down in the Northwest, the furnace is starting to kick in during the evenings, and last night, I cranked up the thermostat to warm up the house. I set the thermostat to 72F against the current room temperature of 67F and the furnace fired up. As usual, it started burning and blowing in the lower setting for a while, and then it switched to the "high" mode and the blower started blowing in the higher setting.

However, after a minute or two in the "high" mode, I started hearing some clicking sounds from the furnace (sounded like relays clicking on the control unit). The clicking was intermittent but erratic with no fixed pattern, but what worried me more is that it sounded like the flame "choking" as if it's on the verge of distingusihing and then burning again. Also, it seems like the clicking sound is somewhat synchronized with the choking of the flame.

First and foremost, I'm concerned about whether the furnace is still safe to use. Then, I'm interested to see what might be wrong with it so I won't be at the complete mercy of the furnace servicemen when they start recommending various [costly] repairs.

A few uneducated guesses:
- is there not enough air/oxygen for the "high" flame to burn (I heard there is a "booster" to feed air into the combustion compartment)?
- is there not enough gas to sustain the flame (I have a 3/4" gas line for both the furnace and warer boiler)
- could it be a bad control unit? (but the low setting seems to work just fine)

Any help, advice or even educated guesses would be appreciated!

Thanks much,
- K.
 
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Old 10-06-11, 04:21 PM
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What you need to do is take the front cover off the furnace and carefully observe what is happening when the clicking noise occurs.

Guessing doesn't cut it. The first step in diagnosing a mechanical problem is careful observation of what is happening.
 
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Old 10-06-11, 11:28 PM
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Thanks for the note, SeattlePioneer. I had a service technician come and look at it today (turns out it was still under warranty from the last service) and he said that my gas valve is "sticky", so the gas flow in the high burn setting was choppy and the flame was buffeting. He quoted the replacement cost to be $700 + tax. I called another Trane dealer and the price was $530 + tax. Seems pretty steep to me for a gas valve and labor, but I suppose the part is no longer manufactured so we're relying on whatever remaining stock one can find. Since the pricing seems to run a broad range I guess I'll keep calling to see if I can get a better deal.
 
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Old 10-07-11, 07:52 AM
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Ummmm. Frankly, I;ve never seen a gas valve that was "sticky" and would turn on/off repeatedly. A sticky gas valve will either not turn on or not shut off reliably.

I'd check the vokltage to the gas valve to see if it is staying on steadily.

Gas valves cost about $150 or so and can usually be installed in an hour or less.
 
 

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