I currently have a 12 year old Natural Gas Armstrong AIR ultra SX 80 that has never had an issue. I just fired it up for winter in Minnesota 5 days ago. Yesterday i noticed that every 3-4 times it tries to start this happens:

1. Exhaust fan turns on.
2. Ignitor lites.
3. Main Burners lite.
4. Burners stay on till right before the blower motor should turn on and then the whole system restarts from item 1 and is fine.

I dont recall a time when it restarted more than once.

I have the original manual but didnt find it of any help other than it says to call your service technician if it doesnt run perfect.....

 

Sounds like you have a blower problem and the furnace is cycling on the high limit. Check the blower and see if it will spin manually.

 

It actually could be so many things, especially seeing this is your first start up. Could be air in the line maybe, tarnished spade connectors or pin connectors borderline not tight inside a jack connector/at ignition module, cobwebs, borderline flame sensor, rusty burners, borderline pilot orifice or flame sense if it has that - and some furnaces use HSI's to sense flame, borderline venting from residual condensate or sluggish inducer bearings from sitting since last season so then maybe it runs the 2nd attempt because bearings loosen up when warmer or ?, causing pressure to be borderline - and much more. Literally, a person would have to check everything, and even then, hope you find it, without shotgun repairing, if the problem is sporadic.

One thing that can help us is to let us know that when it shuts off, what does the inducer motor do?: Does that keep running? or is that shutting off with the flame also? As long as there is a call for heat and the stat is staying closed, doing just that, the inducer should keep running, with most furnaces.

Please keep with us to let us know if this keeps doing this or if it goes away on it's own from use.

And let us know if you have a pilot ignition or hot surface ignitor that glows. And if the problem is the same as you reported, or getting better with time, or not. It coud be the blower motor, as Skip said, if the furance flame has been on for maybe a couple minutes running, first. But if it shuts down much before that, it may not be hot enough to high limit. That is why it can be so many things.

 

It has a hot surface ignitor that glows. Their is one assembly that includes the ignitor, flame sensor, and ground strap.

When the furnace flame kicks out the inducer motor does stay running when the flame kicks off. The problem is not getting better with time.

The burners run for at most 10- 20 seconds before it kicks out.

I pulled the ignitor/sensor/ground strap assembly off and cleaned the flame sensor as it was covered in white build up. It didnt help anything.

 

How did you clean it? Also - all connections and grounding at each end must be good, and also where it connects to the ignition module must be good. Remove the plug-ins there and reinsert. Do you have spade connectors or those pin connectors?

If this is not the problem you need to check the pressure switch circuit to make sure that is not going out on you, before condemning the ignition control module.

 

How do I check the pressure switch circuit?

 

Well, I ended up wiggling all connections and I took off the pressure switch hose and blew through it. The system has now called for heat 5 times on its own without kicking off.

Should I replace the pressure switch hose? I blew through it both ways and did feel more resistance one direction as opposed to the other. Also, the inside of the hose was black in color (red hose).

 

I take that back. Its having issues again starting. Now the exhaust fan starts, ignites fine, burners lite, then it kicks off right as the blower motor starts. The exhaust fan and blower motor stay on while the system restarts. The system ignites and the burners turn on for the second time. Then it heats fine.

Time for a new furnace....

 

You need a voltmeter to test for voltage at the terminals of the pressure switch, while they are hooked up.

When the fire goes away, you have to see if 24 volt ac (VAC)power also is going away for either the incoming 24 volts to the pressure switch, or just the outgoing, neither, or both.

Put one multimeter test probe to one pressure switch terminal, and the other one to good bare metal of the furnace. Then do the other terminal the same way. You have to be down there when the furnace is running, with your probes held in place, and see what the reading is while it is working fine, and what the meter says after the fire goes out.

That is what some have said about their car or lawn tractor, when all they needed was a battery. Seriously. I know 2 instances in my life where people almost gave them (car and lawn tractor) away, simply because the frustration they did not start reliably, and here it was the battery.

 

I measure across the two terminals on the pressure switch. It reads 0 vac up until the system kicks off, then it reads 24vac. Does this mean the switch is bad? How would I determine if the switch is working properly and something else is tripping the switch with low pressure?

Thanks

 

Found this crack while cleaning. Is this the actual heat exchanger or is the heat exchanger behind this? Could this crack be causing my problem?

 

On that particular furnace, I'm not sure if that crack is actually in the heat exchanger or not but on some others of similar design, it is. Call an Armstrong dealer & have them check it out. The heat exchanger might still be under warranty.