Gas furnace needs multiple attemps before starting

I have an induced gas furnace w/intermittent electronic spark ignition (honeywell s8600) that's about 15yrs old. When I call for heat the inducer motor starts, I hear the sparking and can see a flame briefly but the burners do not ignite and the spark flame goes out. I hear a click just before it shuts down. It shuts down and immediately repeats the same procedure. It does this three or four times. It then starts and runs fine. It does this each time, although if the furnace has been running for a while and I shut it down it will repeat the start up attempts only once or twice before starting.

I tried the following:

New T-stat
New filter
Clean furnace/burner area
Clean evaporator coils
Clean flame sensor
Open all dampers

Any idea what this might be?
Thanks.
John

 

I would start by checking to see if the power from the pressure switch to the ignition module stays on or is shutting off, which will shut off the ignition module ignition sequence.

Use an AC voltmeter connected to ground and use the other lead to check the connections at the pressure switch to see if the 24 VAC remains constant once the inducer motor comes up to speed.

 

Was that flame sensor you cleaned lcoated at the pilot burner or somewhere else? How did you clean it?

The pilot orifice may need it's tiny hole unplugged, as you might not be getting a big enough flame, always, to keep enough pilot flame on the flame sensor.

 

What namebrand furance this is ?? and did you look at the control circuit board I know quite few will have indentactor light and you should see the light blinking to tell you the code and what it is doing.

I am thinking a flame senseing device is not working properly that one of few most common way the other issue may be the draft switch is not functioning.

Once we know what model furance you have one of us will able direct the correct way to trobleshooting it.

Merci.
Marc

 

Thanks for the replies.

The voltage is consistent from the pressure switch while the inducer motor is on. The ignitor/flame sensor is located at the burner area and I used an emery cloth for cleaning. I think I got all the holes open.

It never goes into lockout mode. The burners never come on until it finally lights. It very inconsistent. The more its used in a short period of times the less attempts it needs to ignite.

 

When 24 VAC is applied to the S8610 intermittent pilot ignition module, the pilot burner gas and spark are turned on. They continue to run until the pilot lights and pilot ignition is verified by flame rectification.

There is no separate flame sensor--- the metal of the pilot burner hood is used as a flame sensor. Once the pilot is verified as being lit the spark turns off and the main burner gas is turned on.

If the flame rectification circuit was defective, the pilot burner would light and the spark would continue.

If the pilot orifice were plugged up, the spark would continue to run as well.

Since the pilot lights and then goes out, that suggests to me that the pressure switch is opening or the thermostat is shutting off the ignition cycle on the heat anticipator.

Those are the things likely to cause the pilot to shut off and then attempt to reignite again. At least those are the things I'd check first.

 

No specific name is listed on it.

Intercity products
Manuf #1172489208
Model# NHGE075CF01
Serial# N920610709

The circuit board has no lights on it either.

 

On the chance that I was checking the pressure switch improperly I switched it with my second unit. Same thing occurs. It looks as though it is shutting down before the spark has a chance to produce a full flame. I also switched thermostats with my second system but no luck.

Could it be that the system isn't sensing enough gas so it shuts the flame down?

 

Yes, an inadequate gas supply can cause the pilot to light, the main burner gas to switch on and then the burners and pilot to go out, causing the system to start the ignition cycle over again.

You can test that by disconnecting the MV lead at the ignition module or gas valve. That will prevent the main burner gas from turning on.

If there isn't enough gas supply, the pilot would light and stay lit.


Do you have natural gas or propane?

 

I have natural gas. It doesn't sound as though its inadequate gas supply because the pilot lights very briefly then it shuts down but the main burner doesn't come on before it shuts down. The time between attempt to start and shut down is just a few seconds. It sounds as though the inducer motor keeps shutting down and restarting. Once it starts, though, it runs fine and never shuts down.

 

Any other ideas on this issue? I replaced the pressure switch and the ignition module but I'm still having the same problem.

Thanks.

 

Ummm. Guessing about bad parts is not an effective diagnostic method.


Something is switching the burners off, and you need to identify what that is.

Do you have an AC voltmeter (multimeter) and understand how to use it?

I'd measure the AC voltage that powers the ignition module and see if that voltage stays on or shuts off when the burners shut off. If it stays on, everything up to that point is OK and something (like inadequate gas pressure) is shutting off the burners.

If the 24 VAC goes away when the burners shut off, you need to trace that back to see what is shutting it off.