Lennox 90ugf problem

Problems related to residential installations.

Lennox 90ugf problem

Postby mlijoi » Tue May 08, 2012 7:20 pm

Hi all great forum.

I have a problem with my 9yo lennox 90ugf furnace. The symptoms are as -

Thermostat calls for heat.
Blower runs
Ignitor glows until red-hot
gas valve 'clicks' or 'thunks'....no flame ignited
gas valve makes another thunk and ignitor goes out

This process happend for 4 times until finally lighting but now since i've replaced the ignitor with a new universal one made by Honeywell it never lights and shuts itself down. I'm at a loss as to what it could be! PLEASE help!
mlijoi
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- Lennox 90ugf problem

Postby mlijoi » Tue May 08, 2012 10:33 pm

Ok, any tips on where I should begin? how are the orfices cleaned and crossovers?
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- Lennox 90ugf problem

Postby heatseeker » Wed May 09, 2012 8:40 am

Why would you replace the ignitor if the old one was glowing????? Call a company now before you replace all of the parts and it still won't work,. save yourself the headache.
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- Lennox 90ugf problem

Postby Freon » Wed May 09, 2012 11:02 am

Is it possible, with a long stick match, to reach the burners where the HSI is located? If so, when this cycling starts, see if you can light the burner manually with a match. If you can, then it would appear there is not a clog and possibly the HSI, although glowing, isn't getting hot enough due to age.
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- Lennox 90ugf problem

Postby mlijoi » Wed May 09, 2012 12:35 pm

Well the old ignitor was glowing red hot as is the new one. I replaced it due to the idea that it wasnt glowing hot enough or long enough and so i replaced it. I dont know how to prove or disprove gas is getting to the orfices without a manometer (that the gas valve is indeed opening and the orfices aren't clogged.
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- Lennox 90ugf problem

Postby heatseeker » Wed May 09, 2012 2:41 pm

you need to stop now. call a company.
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- Lennox 90ugf problem

Postby mlijoi » Wed May 09, 2012 3:13 pm

Got some advice that it could also be the circuit board?? Is that plausible?
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- Lennox 90ugf problem

Postby mlijoi » Wed May 09, 2012 3:16 pm

heatseeker -
> you need to stop now. call a company.

I dont want a tech to come over charge me $100 plus taxes to sell me a part at 300%
Mark up. Some of us are unemployed with tight budgets!
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- Lennox 90ugf problem

Postby heatseeker » Thu May 10, 2012 8:06 am

If you keep fudging with it you will be unemployed and homeless. The price markup covers many more things than a part, its very expensive to operate a hvac company and then listen to people whine about a couple hundred bucks.
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- Lennox 90ugf problem

Postby Freon » Sun May 13, 2012 1:40 pm

Again, try and light the burners manually with a long match. The gas valve will open and you have a short time to get flame or the safety will close the gas valve. It is possible rust may be interfering with the flow of gas from the orifice or something else is happening. But if you can't manually get a flame then you know you don't have gas flowing where it's needed. I am surprised you can't hear the gas after the gas valve opens.

You might also disconnect the gas valve from the furnace burner and see if there's gas flow when the gas valve opens. Possibly the gas valve sounds like it's opening but isn't. If there's a port on the down stream side of the gas valve (just before the burner and after the valve mechanism) open it and see if there's gas flowing when you call for heat.
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