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Drew1315
Drew1315, HVAC Technician
Category: HVAC
Satisfied Customers: 88
Experience:  I was a Building Trades Journeyman in the Sheet Metal Union for over 11 1/2 yrs.
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We have an Armstrong Furnace Ultra SX 80. Model #GUJ100D12-3A,

Customer Question

We have an Armstrong Furnace Ultra SX 80. Model #GUJ100D12-3A, Serial #8499G36777, installed in the fall of 1999. We had some trouble last year and had a furnace tech out and he said we needed a bunch of parts. We have used the unit this year since the heating season began with no problem. We do not keep the furnace on all day. We heat it until it gets to 70 in the morning and then we turn it off at the thermostat. We may or may not heat it a few times during the day, or it stays in the off position until the next morning. We only use two fills of propane per year (500 gal. tank) due to the way that we use the furnace and the fact that we have the benefits of passive solar (lots of south facing windows) and excellent insulation. We also have the good sense to put on a sweater if we're chilly! That propane is also used to heat water and cook.

Yesterday when I turned the furnace on in the morning, the exhaust fan started like it should, then the glow coil turned on, then heard the click of the gas valve, but the burners did not light. The glow coil turned off. Then the same process began all over again. I turned off the furnace at the thermostat. Then I unplugged the furnace from the wall (it's powered by a heavy duty three pronged plug and 12-2 w/ground house wire). When I did this, I heard a click (like the gas valve turning on) and then nothing. I plugged the unit back into the wall socket, turned the thermostat back on and voila! the furnace turned on like it should. We never let the furnace cycle for a second time, but today, we did, and the furnace turned on like it should.

My husband is a retired Columbia Gas Serviceman, and between us, we suspect either the control board (which I understand has had at least one revision) or the gas valve.

Can you tell with certainty which of these parts need to be replaced? If you need further diagnosis, I would be happy to correspond with readings from a volt/ohm meter if you will tell me the points to check between and what the reading should look like if it is healthy. We would love to have a furnace tech out again but we're afraid to get cheated by unscrupulous people, which we suspect these last guys of being.
Submitted: 2 years ago.
Category: HVAC
Expert:  Drew1315 replied 2 years ago.

Drew1315 :

Hello, My name is XXXXX XXXXX I will do my best to assist your issue.

Drew1315 :

Are you able to observe the HIS (glow plug)?

Drew1315 :

HSI****

Customer:

yes

Drew1315 :

HSI = Hot Surface Ignition

Drew1315 :

ok, do you know when it was the last time this may have been replaced?

Customer:

?

Customer:

the furncae was installed fall of 1999. it's in the same condition as it was purchased.

Drew1315 :

Typically the HSI can go bad and only light the burners intermittently. This can sometimes be visible if it has a small hairline crack

Customer:

what does HSI look like?

Drew1315 :

While observing the HSI, sometimes there will be an abnormal wear

Drew1315 :

that is the glow plug

Customer:

duh, sorry Im so uninformed

Drew1315 :

no it's ok really

Drew1315 :

that is why I / we are here.

Customer:

Is this our problem? Anything else to say

Drew1315 :

The true way to know if that glow coil is bad would be to ohm it out. But, the downfall is knowing what the OHM reading should be.

Drew1315 :

It very well could be the issue.

Drew1315 :

I think that an OHM reading approximately 5 ohms is a general number

Customer:

I suspected this at the very first, but it worked....just didn;t know it was intermittent. Thanks!

Drew1315 :

Hearing the gas valvve click in the manner it is, informs us that it is opening

Drew1315 :

correct. Sometimes it will light the burners and sometimes it will not.

Drew1315 :

Generally an inexpensive part

Drew1315 :

and all it does is plug in. the biggest issue with changing them is you do not want to touch the glow coil itself, nor do you want to bump it on anything.

Customer:

And the fact that it's getting the order to "click" means the control board is okay, yes?

Drew1315 :

in a matter of speaking yes. everything that you are explaining seems to be a normal sequence of operation

Drew1315, HVAC Technician
Category: HVAC
Satisfied Customers: 88
Experience: I was a Building Trades Journeyman in the Sheet Metal Union for over 11 1/2 yrs.
Drew1315 and 4 other HVAC Specialists are ready to help you
Expert:  Drew1315 replied 2 years ago.
If you would like to continue further with this please do not hesitate to click my name. I will be more than happy to continue assisting.

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