Exploding 23 year old carrier

[gandl]

Here is the situation. Went on a call yesterday. Homeowner complained when the furnace came on it exploded real loud. He is absolutely right. On a call for heat. valve opens up, you can hear gas flow, but wont light. After a very length of time, it ignites and blows fire out the front sometimes two feet. which knocks out the pilot. Changed the valve, pulled the orfices and burners and wire brushed them and blew them out with air. Pilot is good and strong.
My question, do the burners have to place back in a sequence. I didnt think so cause i have cleaned several and never put them back in any certain way. NOte, that this furnace has been leaking water for quite a while cause the a coil drain line was clogged. water in the base of the furnace in the blower compartment. The burner chambers have evidence of heavy rust. Thought maybe heat exchanger rusted through but didnt think that would cause it not to light. Never run into this problem. Maybe some of you with more experience have and can give some advice on what the problem might be. Incidnetly, a couple of times it did light, one time only one burner lite and the other time three out of four lite.

[hvac_czar]

The problem? 23 year old furnace with little or no maintenance, that's what... Heavy rust in the HX? Water through the furnace? You replaced parts on that POS? Cost vs. benefit, think about it.

[beenthere]

LOL, some times you should talk to the ho about replacement, before you try to fix the unit, this was one of those times.

Did you check the manifold pressure.

Did you blow out the manifold.

Does your company have enough margin on swap outs to discount the service call if they change out the furnace.

[Milk man]

You may have a burner cross over restricted. Reclean burners and pay attention to the carry over slots.

But first, as said above, talk to HO about a new furnace. There are dimples in the heat exchanger that rust out. It's hard to find without a water test.

[krd]

Generally most servicemen try to put the burners back in their original slot, but it is not mandatory. When you buy new burners they are not numbered 1,2,3,4 etc. However that explosion you described is a updraft blockage most likely caused by the rust. High gas pressure and blocked tubes contribute to the problem. Be careful of what you are doing. If it happens again for any reason and a mishap occurs the liability goes to the last person who worked on the equipment.

[Midwest]

In addition to cleaning burners and cross tubes, make sure you have positive draft flow. Had an LPG furnace once that lit with a serious bang. Discovered it was experiencing a slight downdraft due to a damaged vent cap and vent piping too close to roof line. Corrected draft problems and lighting smoothed out, but also I cleared a lot of lint from the burners and cross over tubes. If a little lint can disturb proper ignition, just imagine how a bunch of rust particles can do the same or worse.

[Mr HVAC41]

i had a furnace blow up in my face in vocational school i was standing off to the side as i was taught to do with a 'strange' furnace. scared the crap outta me. and i never went near it again except with the temptation of getting a hammer and saying 'things' of a strong nature under my breath every time i looked at it!

now,if a furnace blew up on me again, i would condemm the pos faster than the homeowner could run down to the furnace to see whats going on!

[bittan]

Sounds like a lot of time and money going into a LIABILITY

[Mr HVAC41]

it is 23 years old and i wouldnt trust the thing with a dime in the first place, so why would you trust it with your life. oh yes home owner! it does have some control over your fate this winter as you sleep in your nice warm bed at night thinking how nice it is to have heat. next thing you know beep beep beep goes the co alarm and then bang! fire alarm goes off 30 seconds later! KILL THAT CARRIER AFORE IT KILLS YOU!


you have been warned!

[Special Ed]

Originally posted by gandl
After a very length of time, it ignites and blows fire out the front sometimes two feet.

And how did you get this measurement?:D

[Mr HVAC41]

he measured how far up his arm the hair had disappeared.

[Special Ed]

LOL!!

[timmay]

did you check the hx for cracks.
Thats the first thing i do on any system 20+. i don't even look into their problem until I've made sure that HX isn't compromised.

Acrtually thats a lie the other day i went on a clean and check and cleaned it first. It looked like it was burning good. the HX looked clean but it was 30 years old. so i pulled the blower to oil the motor and then i did a water penetration test. The water rained down like a waterfall. Hell if i had done that first i would of been out of there in 20 minutes.

[markwolf]

On some of the older carriers you will find the pilot bridge pinched shut on the left & right sides.........Yes it does matter which way you put them in if that is the case!Shoot us a model number & I will tell you where the heat exchanger is failed haha!Also some furnaces require a slow opening valve.Is it propane or nat?

[djsreps]

The water test of the HX. Never used water just looked for draft comming out of the HX when the blower is on. How much water and where to put and look. Just guessing put x ammount of water in the flu and look inside the HX? What if the Top of the HX is rusted what good would the water do?

[Mr HVAC41]

what is a water test? never heard of it before

[Milk man]

On a trailer furnace, pull the blower and burner. Look inside HX with a good flashlight and mirror. Then with a garden sprayer lightly coat the outside of the HX. Look inside for water leaking in to the HX. Pay attention to the rivot that hold the baffle plate up.

You can do this on regular furnaces also. just takes a little more effort to crawl into the blower housing and spray up.

This works to find bad heat exchangers on standing pilots furnaces.

[Milk man]

On this carrier the water needs to be sprayed high enough to reach the dimples, or gain access to the top through the delta plate of the evap or if your lucky enough and the coil is raised above the furnace enough .

If the dimples are rusted through you will be able to spot it.

GOOD MIRROR AND FLASH LIGHT. Not the little mag lite that are carried on our belts. I use a mirror about 2 foot long and inch and a quarter wide.

[Edited by lynn rodenmayer on 10-03-2005 at 09:54 PM]

[berad]

Originally posted by lynn rodenmayer
You may have a burner cross over restricted. Reclean burners and pay attention to the carry over slots.

But first, as said above, talk to HO about a new furnace. There are dimples in the heat exchanger that rust out. It's hard to find without a water test. Exactly, also some burners have a little scoop inside them that catch gas and push it into the crossovers. If that scoop rots out hang it up get new burners. 23 yearw old get new furnace.

[mavericknga]

sounds like backdraft problem,check vent for restriction found a bird nest in one causing similar problems

[timmay]

I use a pump bug/weed sprayer. The stem is thin enough to jam way up between the chambers. That and a long mirror with a flood light. I condemed 2 on friday.

[bittan]

Lynn, the technique you described is something I just learned recently. Attended a training seminar by "Heat Exchanger Experts" out of Ft. Collins, Colorado. Long thin mirror, powerful flashlite, flexible sprayer. They provided 50-60 furnaces and heat exchangers by many makes and models. They specified where to look on each model for cracks. A great "hands-on" learning experience.

[djsreps]

Bittman sounds like a really good seminar. Im jealous. I like seminars one can learn from and not all a big sales pitch party. And Lynn I like your use of the term delta plate for the triangle ends of an typical A coil. Evap coil's delta plate good name.

[Carnak]

hissssssssssssssssssssss, spark, spark, spark, boooooooooooooooooooooom

[Mr HVAC41]

you have no idea how true. of course, if a furnace did that to me again(yes it happened once before) those would be its last words! i reallt ought to get a chain saw with a metal cutting chain if possible. i would like to have it to just sit it next to the h.o. furnace while i work on it. then if h.o. asks what thats for, i say that is what i disable furnaces with. if they do something i dont like, i am required to disable the furnace. usually i shut off gas and kill pilot but somehow they get fired back up. i dont like that so if i need to use it, i will. then take it out of its case and hold it like a baby and start talking to it:

thats right saw isnt it? we likeses to destroy bad heaters yes we does!... then watch the ho eyes get big. then just for kicks, the same applies to condensers and i tell them so.

and just cause, go outside and take only the saw. then start it up and watch for the ho to come a running and hold the saw just above the condenser and say, its okay, i'm just fixing a leak!

[CityHvac]

Originally posted by berad

Originally posted by lynn rodenmayer
You may have a burner cross over restricted. Reclean burners and pay attention to the carry over slots.

But first, as said above, talk to HO about a new furnace. There are dimples in the heat exchanger that rust out. It's hard to find without a water test. Exactly, also some burners have a little scoop inside them that catch gas and push it into the crossovers. If that scoop rots out hang it up get new burners. 23 yearw old get new furnace.

Just to add.....check that the pilot is close enough to the burner to light the burner when the gas valve opens. I have also got dirt/rust in the gas orifice next to the pilot, so when the gas valve opens the gas builds up from the next burner over and bang it finally lights. For years now, after reinstalling the burners, I use my small flexible inspection mirror and check all the gas orifices BEFORE I light it up.

[gandl]

AFTER READING ALL THE POST, I TOOK SOME OF THE ADVICE. FIRST RECHECKED AND CLEANED THE CROSSOVERS. THEN NOTICED THEY WERE GAPPED QUITE A BIT. CLOSED THE GAP ON THEM AND REINSTALLED THEM. AND GUESS WHAT, LIGHTS VERY GOOD AND BURNS REAL GOOD. DONT KNOW HOW THEY GOT GAPPED OPEN SO MUCH. THANKS FOR ALL THE INFORMATION. THIS BOARD IS VERY HELPFUL.

[Mr HVAC41]

welcome! i find most everyone around here knows quite a bit more than i do thusly its a great learning place