Old Sears Forced air Heater - Pilot blowing out when Fan comes on -867.76572

[Tone Blair]

SORRY NO MODEL NUMBER

 

Working on an old downflow forced air heater.

 

The pilot blows out when the fan kicks on.  It seems like its going to work, then even after the burner turns off and the fan keeps going, the pilot will blow out.

 

Vent is clear, heat exchanger is a little dirty, rusty, but no visible signs of cracks.  Thoroughly cleaned heat exchanger and surrounding areas

 

New safety valve, pilot assembly, fan/limit switch, and filter. Same problem.

 

Is this an indication that the heat exchanger is cracked? Is the fan blowing too hard?  Can we "shield" the pilot?

 

TIme for a new heater?

 

[Tone Blair]

Oh, this is a 24 volt, standing pilot system, new thermocouple.

 

THe pilot is just flickering out.

[applianceman97]

Tone you know the rules about the model number brother. We cant help much at all until we have that info

 

I should be deleting this topic because no model is in the title but i have a cup of coffee in my hand and im in a great mood today. For future readers and you as well Tone, Writing "no model number" in the topic title does not avoid the deletion of the thread. 

 

So since rules are rules I will just postpone the deletion of this topic to give you a chance to post it up. you have unit 5:36 PM pacific time to post your model number.

 

(gotta have fun in the morning right???)

[Tone Blair]

Fun in the morning is getting in your truck and realizing your passenger window was smashed out and your tool bag is gone right before you have a major heater to repair. Thats fun!

How bout you delete this topic, so we can follow the rules and we dont let people out there see this, cuz then theyll try to do the same thing, and we cant have that!

Ill get the model and post a new topic, i just hope i can get an answer!

[m_west5]

Is there a film of black soot in the home, on horizontal surfaces? If so, probably a cracked exchanger.

Is the thermocouple properly positioned in pilot flame?

Does it have a pcb controller? Did you check for a continuous 24vac while starting and running?

Is the fan air blowing directly at the pilot? Alignment issue?

Recurring problem or just happened this heating season?

Edited December 4, 2014 by Radio Loco

[Tone Blair]

MODEL NUM 867.76572 super old sears, at least 30+ years old so I doubt the model will even come up anywhere.

Again, just a basic forced air Downlow heater, 24 volt system.

Radio loco, thanks for the response.

No soot anywhere.

Tcouple positioned properly.

No PCb

I didn't check for continuos 24 volt, but it seems like it was fine.

I don't think the fan is blowing directly at the pilot, but there is definitely a draft.

As far as I can tell the alignment is fine.

Visually I can not see any cracks in the heat exchanger, but I know you can't always see them.

The burners are burning good, real nice blue, the flame isn't lifting, so I didn't feel like the exchanger was bad, but I'm not 100% sure.

Sears was out on the unit before me, so I don't know if they installed a different pilot assembly than the original, I installed a new pilot assembly and t couple, but I was replacing with the same style pilot.

The only time the pilot has problems is when the blower is on.

Do you think retrofitting the unit with an intermittent kit would help solve the problem?

Thanks.

[m_west5]

Hi Tone, wow that is old. How you described the flame, it sounds like the heat exchanger is not bad. Not many gas heater calls here in the desert (mostly heat pumps), but on that rare call, I always clean the exchanger very, very good. Then use a super BRIGHT light and an inspection mirror and go over it many times slowly. You will see a hairline crack, if there is one.

"I don't think the fan is blowing directly at the pilot, but there is definitely a draft. As far as I can tell the alignment is fine." 

Where do you think the draft is coming from? Could you please provide more detail? Does it appear the cabinet was reassembled correcrly after all the work that was done? Missing interior panel?

"Do you think retrofitting the unit with an intermittent kit would help solve the problem?"

Sorry, but I'm not sure what this is. Could you describe?

[Daveb1972]

Draft is likely from natural draft as the HE cools. The burner dies then the pilot dies would lead me to 2 possibilities.

1) draft diverted plugged/missing, exhaust replaced recently? Modified?

2) case to HE flange in vestibule leaky. The seam between the two may be bad.

Watch flame of main burner as fan turns on. If flame is disrupted then HE failure is likely. Look in blower housing for weird rings. If you find them (in blower housing under squerill cage) then HE has failed. Look at the seam for the heat exchanger where the burners enter. There is some surface that is common to vestibule, burner, and HE. This should have a gasket that may have failed.

Describe type of HE ie: barrel, s type etc. pictures are nice too.

I think you will see the main flame disturbed when blower starts and that USUALLY means failed HE.

Intermittent kit may solve it, or rather may avoid the issue.

You can also try a combustion analyzer and watch for co2 or co changes as blower starts (bad HE)

[applianceman97]

Model # added to topic title.

 

Thanks brotha Tone!!!

[Tone Blair]

Hey guys long time, but I finally got back out to check it, and the exchanger was absolutley cracked!

Thanks for all the help!