Delayed Ignition "boom"


  #1  
Old 01-02-03, 11:28 PM
leezzzzz
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Delayed Ignition "boom"

My problem is very similar to tMason's post (on page 2) about a delayed ignition problem...

my symptoms are as follows.....

Our basic 40 year old Lennox furnace (checked & serviced last year) has developed a delayed ignition problem that occasionally causes the unit to make a duct rattling boom...

to say the least, this can be unnerving...

The burner slots all appear to be open & clear...

the pilot flame appears to be the correct distance from the "front feed runner"....

the combustion color is not quite as blue as recommended...

& I have been leaving the furnace's door off to prevent overpressureizing the "fire box" during these delayed ignition events...

My chief suspect is partially clogged ignition feed runners....I have (4) & the pilot is mounted on the second from the right...

The runner slots appear to have metal corrugated wafer inserts, that I assume are there to retard the flow of gas...

I've cleaned the main burner slots before with an exacto razor saw & moderate tapping with a 2X4 block....

but I never had much success cleaning the ignition runners because the wafers are in the way...I'd like to know what the most effective tools & procedures are for doing this chore?...


thanks, Lee / Columbus Ohio
 
  #2  
Old 01-03-03, 06:56 AM
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Hello: Lee

It's possible ambient temp plays a factor in the problem. Contraction when cold may effect the burner and or ignition slots and ports. The trick is to determine exactly where the flow of gas is getting restricted.

In order to do this correctly, it is often required to remove all the burners and clear all burners, ignition slots, ports and passages. Invisioning how the gas travels, it's path, once it leaves the orificies to get into the burners helps to located the problem.

There are also several other possible non easily correctable problems. Many of them have to do with the firebox and it's physical condition, the vent exists in the firebox, flame charactoristics, pilots flame charactoristics, air to fuel ratios, etc.

Many times it takes a well trained professional with a sharp eye for detecting the problem and knowing how to correct the problem and or what to do without replacing parts.

Since the unit is 40 + years of age, there may be conditions which cannot be corrected. A damaged firebox is possible. If this condition is the cause, the entire furnace will need to be replaced.

Regards,
Tom_B
 
  #3  
Old 01-03-03, 07:26 AM
leezzzzz
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(TOM) re: delayed ignition

Thanks for the great suggestions Tom...

did you have any suggestions of methods for cleaning-out the "ignition runners"...

also, if the runners can't be cleaned sufficiently, are the burners replaceable on my old Lennox, & if so, what might those cost?

They are a very heavy casting...

about 24" long x 1.5" wide...

w/ right angle ignition runners up front, about 3.5" long...

the front inlets are funnel shaped w/ rotary air adjustment plates...

thanks, Lee/Columbus/GoBuckeyes!
 
  #4  
Old 01-03-03, 05:53 PM
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Hello: Lee

Replacing the older style cast iron burners should not be necessary. If the around holes or ports are restricted, try a coat hanger wire. However, I have not seen a cast iron burner that needed replacement simply from years of usage.

If the burners have slots, try the back of a thin hack saw blade. This usually works and fits into the slots. If not, being creative is required. I am sure you'll find something.

I mentioned ignition "runners." Not sure I know what your referring to???? If it is the means by which the burners light each other, imagination is required to find the means to clear any restriction. I'm sure you will find the correct item or tool, etc to clean or clear them without causing any damage to them, etc.

If the hole in the runners, as you refer to them is resticted or clogged, etc, use the metal wire from the coat hanger to clear them. Flushing with water helps if the burners are removed.

Do not adjust the air shutters on the ends of the burners. They should remain as set unless there is some problem with how the flames are burning. These are the parts you refer to as: "funnel shaped w/ rotary air adjustment plates"

The air shutters control the air entering the burner. If the flames are burning correctly, the shutters must not be adjusted.

About all I can help you with at this time Lee. Try the cleaning methods suggested. I'm sure they will work for you. If you remove the burners, be positive to re install them EXACTLY as they where prior. Very important. Check for gas leaks on any parts where gas is present after any burners etc are reinstalled.

Good Luck,
Tom_B
 
  #5  
Old 01-08-03, 09:43 PM
leezzzzz
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Talking delayed ignition boom

Tom...

The use of water to rinse out some of the "burner to burner runners" passages was one technique I haden't thought of...

I bet it will solve my problem...

Thanks for the additional ideas...

 
 

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