Question
Before I blow up the house…

This past summer, I scheduled an “annual” inspection by the gas company
(in quotes because it has been several years). The inspector found a
problem with the flue pipes and tagged the furnace.

I had the repair work done and called the gas company to send the
inspector back out. He came out, inspected, and removed the tag.
However, I discovered this evening, as the house finally got cold enough
for me to notice, that he neglected to turn the gas back on. I mean
there’s the gas pipe, and it’s got a valve on it, and the valve handle
is at 90 degrees to the line. So that pretty much tells me the gas to
the furnace is not turned on.

Okay, so here’s the stupid user question. Do gas furnaces still have
pilot lights that require lighting when the gas is turned on, or do they
have electric ignition and just need the valve opened to start working?

I should add that this is a Bryant Quietline furnace of unknown vintage
but at least a decade old, probably more like two decades, if that makes
a difference in answering the question.

If nobody here knows the answer, I’ll call the gas company tomorrow and
use extra blankets tonight. I don’t want to call them now and then have
to wait up all night for them to show up and tell me what an idiot I am.
Answers
Ok, a couple of things. First of all, you mentioned you couldn’t hear because of
the fan. Is your thermostat set to have the fan on ON, and not AUTO? If it isn’t
there already, set it to auto (mainly so it keeps quiet to aid troubleshooting).
I ask this because typically the blower fan doesn’t start until the plenum gets
hot or a set time after burner ignition. Or do you mean you hear the draft
inducer blower running? That’s a much smaller fan that blows the exhaust out of
the furnace, and yes that one should come on immediately after the call for heat.
Not all furnaces have an inducer fan, older ones would be less likely to have
this.

You mentioned (I think) there are two furnaces, side by side. For now, just pick
one and concentrate on that. Do both furnaces have a separate manual shut off on
the gas line?

If it has a pilot, the control knob I referred to would be on a valve unit inside
the furance. Just follow the gas line inside the furnace until you get to
something that looks like a valve. If it is electronic ignition, it will not have
a knob, if it is a pilot ignition, it will..

I assume your furnace is single stage. (i.e. it’s either on or off, no low or
high). I’m also assuming it is not a high efficiency furnace and the exhaust flue
is connected to a chimney.
If the furnace is electronic ignition, the sequence of events is controlled by a
circuit board and goes like this:
1.) Thermostat calls for heat (closes a 24 volt control circuit)
2.) Draft inducer fan (if equipped) starts and positive draft verified.
3.) Ignitor is energized, which gets extremely hot. (takes 10-30 seconds usually)

4.) When ignitor passes ready test, main gas valve opens, supplying the burner.
The hot ignitor ignites the gas.
5.) Positive burner ignition is detected and gas valve is permitted to remain
open. If not, a fault is detected (possibly recorded) and main valve is shut off.

6.) After a minute or two, furnace is hot enough to run the main blower, which
starts on its own thermostat or via a timer.

If it is pilot, it is much simpler.
1.) Thermostat calls for heat
2) Draft inducer fan starts (if equipped)
3.) Gas valve to burner opens. The burner lights immediately from the pilot.
4.) Blower fan turns on as above.

Do you know the model number of the furnace? Perhaps I can find better
information based on that.
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• Answer:You may need to have the burners cleaned. There’s nothing wrong with the gas valve if you’re getting any kind of flame. the cleaning should be done by someone who knows what they’re doing, a.k.a. a professional.

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