Furnace pilot lights, but 30 sec of clicking before starting

Problems related to residential installations.

Furnace pilot lights, but 30 sec of clicking before starting

Postby matthewjadams » Sun Sep 18, 2011 10:22 pm

Hello,

I have a gas Carrier furnace, Model 58GS100-GB.

It's getting a little cooler here in Chicago, so I decided to make sure my furnace is working properly. When I turned up the heat the first time, I heard a lot of clicking, perhaps 30-60 seconds worth, before the whole furnace started up. I was a little concerned that the furnace wasn't sparking well or that there was poor air flow, so I turned off the furnace and then watched it ignite as my wife turned it on.

Almost instantly (the first click?) a small light ignites (it isn't always on, so I assume this isn't a pilot? forgive my ignorance), but the clicking noise continues for 30-60 seconds before the main gas is opened and the full flames occur. Within a certain time period, the fan turns on, and we have hot air. All of the flames appear to be a clean bright blue.

My questions -

I believe that the clicking is a sparking ignition, and it continues even though this little pilot is lit up right away. Is this normal?
Is that little light called a pilot light, even though it isn't always on?
What mechanism detects this pilot is on, before it turns on the main gas flow?

Thanks in advance for your help,

Matt
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- Furnace pilot lights, but 30 sec of clicking before star

Postby heatseeker » Mon Sep 19, 2011 8:41 am

it is normall for it to continue clicking until the controller senses the electromagnetic charge from the senser. If it takes to long it may need cleaning the senser that is.
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Postby Freon » Tue Sep 20, 2011 3:29 pm

I strongly suggest you go to the furnace and listen and watch while another person calls for heat. If you have a spark ignition then the clicking could be the spark sound or the gas valve. Since you hear it, I think it may be the gas valve.

Usually, when you call for heat, the control board opens the pilot light valve and the spark ignites the smaller pilot flame. Now there is a sensing circuit (for safety) that determines if the pilot flame is on. If the sensing circuit "sees" the pilot flame, it opens the main gas valve and you have heat. If the sensing circuit does not see flame, it shuts everything off and retries.

Usually the sensing circuit is dependent on electron flow through the pilot flame. If the 2 electrodes (the spark emitter and ground to which the spark arcs toward) are dirty from rust, the sensing circuit may not see enough current to think there is a flame. Also, an old control board can cause the same symptoms.

That's why it's important to know exactly what is happening at the furnace when you call for heat. If the noise is the gas valve then you can carefully clean the pilot assembly in hopes it is rust causing the low current flow. Be sure to turn off the furnace power when working on it. Also make sure all electrical connections are secure. If that does not help you may need a new control board.
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- Furnace pilot lights, but 30 sec of clicking before star

Postby heatseeker » Wed Sep 21, 2011 12:51 pm

brilliant.
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Postby Beach » Wed Sep 21, 2011 11:07 pm

steps of furnace

upon call for heat the inducer motor starts.
when proper signal of motor is read the pilot is then started.( like Freon stated there are several things that can go wrong here)
after pilot is lit the main valve is turned on and your burners should burn
once it reaches a certain temp your blower should then kick on. ( not necessarily reading "temp" to start blower)
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