Gas Hot Air Furnance on/off every 2 minutes


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Old 01-11-09, 11:33 AM
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Gas Hot Air Furnance on/off every 2 minutes

I have a Bard gas hot air furnace that is recycling on and off. It goes on for 2 minutes and then off for 10 minutes on the automatic setting. It stays on when on the manual On setting. The furnance is 15 yrs old, Bard Model IH115D48B

The temperature of the house depending upon the outside temperature is at the setting or a few degrees less than the setting. The day settings very depending upon week or weekend at 64 or 67.

I took out the flame sensor and it looked clean and not sooty but I cleaned it anyway with steel wool and emory cloth. Filter is not clogged. Flame at the igniter looks good and the flames at the bottom all look good. The plastic hose to the pressure switch is not clogged.

Prior to the cleaning of the flame sensor, I replaced the thermostat. With the old thermostat, the fan would run and blow out cold air. I know after the furnance made heat and then shut off, the fan would continue to run for quite a while until the air became cold before shutting off.

What can I test out next, procedure for testing, or what should I replace?

Do limit switches fail often? Pressure switches? Transformers? Where do I go for testing information? I read on the net to take an volt meter to the transformer, ground one, and when the furnace is running, every terminal (5), should read 24 volts. Only 2 of the5 are reading 24 volts, the others are reading 0 when the furnace is running.

Also on this furnace is a Honeywell box 2"x2"x5" that all the wires clip on and the flame sensor goes to. And there is a small rectangular box with wires that looks like like a relay switch on a car.

I was just near the furnace and I heard a click, sounded like it was coming from the transformer, and it almost sounded like a magnetic relay was opening or closing but nothing happened on the furnance.
 

Last edited by JLawrence08648; 01-11-09 at 01:02 PM. Reason: Added another replacement, thermostat
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Old 01-11-09, 11:59 AM
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Your furnace is operating, but apparently not staying on long enough to bring the temperature up all the way.

That could be caused by the thermostat shutting off too early, a pressure switch opening and shutting off the burner, or the limit switch opening because the furnace is overheating.

What you'll probably find is that if you turn the thermostat 'way up --- to 80 degrees or so, the furnace will reliably stay lit until it shuts off for one of these reasons, or perhaps another. That will allow you to observe in detail what is happening when it shuts off.

For example, does the fan motor continue to run? Does the furnace cycle back on again after a while, or does it stay off and the furnace blower fan wind up shutting off?

I'd also use an AC voltmeter to determine which of those likely causes is shutting off the burners. Check at the thermostat wires, limit switch and pressure switch to see if one of those is opening up to shut off the burners.

Also, what's the model of the Honeywell ignition module? Are their any flashing error codes on the ignition module or circuit board, and if so what does that code indicate?


It's worth checking to see if the filters are plugged, a common cause of the limit switch opening in cold weather and causing this kind of problem.
 
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Old 01-11-09, 12:59 PM
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Prior to cleaning the flame sensor I've replaced the thermostat. With the old thermostat, it was cycling on and off as it's now, but the fan was on and blowing cold air and then the fan would shut off. When I replaced the thermostat, the fan now wouldn't continue to run so therefore no cold air.
 
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Old 01-11-09, 01:07 PM
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I'll bet on thermostat issue. Either it's location is in field of heat in the house, or it's anticipator setting is too low, or swing temp on a digital stat too low (if you have such a choice of temp swing adjustments that can be made) -be my first guess and things to check.

Easy to test with meter at the 24 volt power strip in furnace where stat wires hook up is to see if W (white wire/return heat wire from stat) terminal-to-ground current goes away when furnace prematurely shuts off. Also if you had no test meter you could use a piece of wire to jump between R and W terminal, which would bypass the stat) to see if furnace continues to burn until you unhook the jumper.

[!The jumper must not be forgotten, and must be unhooked! This would just be used for a short test run!]

....................................

Huh. You oddly enough chose to answer about the stat to SP while I was typing. I'd STILL check to see if power is shutting down at W. It may simply be location of stat causuing this, and coincidently you may never have set "swing temp" degrees/anticipator correct on either stat.
 
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Old 01-12-09, 06:08 AM
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I said in my original post that the furnace stays on when in the manual On setting. I was wrong, it cycles on and off but not as often as it does on automatic. On automatic it only stays on for about 2 minutes.
 
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Old 01-12-09, 09:24 PM
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You need to turn the thermostat down so that the furnace is in a stable off situation.

Take the cover off the burner compartment. Post the make and model number of the furnace from the rating plate inside the burner compartment.

Then turn the thermostat up and carefully note the sequence of events that happens, in detail.

You may need to repat that a few times until you are satisfied you are recording everything.

Post that information here, and perhaps we can help you.
 
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Old 01-16-09, 08:03 AM
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Blower fan not going on

Seattle Pioneer asked me to sit and watch the furnace and watch what was going on, great idea. I discovered something. The fan blower motor is not going on. We had this replaced in August for the ac. Isn't the fan blower motor supposed to go on and start blowing hot air through the house?

I have a 12 yr old Bard, gas hot air furnace, Model #IH115D48B

Reviewing things.
We were having a problem and I replaced the thermostat. Still a problem below.
Right now watching the furnace through the automatic setting for 10 on/off cycles.
The furnace runs for 1 minute and then turns off for 5 minutes very consistently.
During this time, the blower induced fan near the top of the furnace goes on and then there's a clicking noise from either the Honeywell box or the Deltrol Control relay maybe, then the electronic ignition lights the pilot flame, then the burner tubes light, this runs for one minute, then shuts off. During this whole time, the blower fan below does not go on.

I put a voltmeter on the 5 screws of the transformer when the furnace is on and only 2 of them have 24 volts, the others have 0.

Help, what's wrong? I'm not sure what everything does. Do I replace the transformer? There's also something that looks like a magnetic relay next to the transformer. What gets replaced next and then what gets replaced after that? Is the transformer and the magnetic relay propreitary or standard? I don't hear anything clicking or making noise on the transformer or magnetic relay.
 

Last edited by JLawrence08648; 01-16-09 at 08:16 AM. Reason: put make & model # in post
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Old 01-16-09, 09:44 AM
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If the fan isn't operating to circulate warm air, I'd say we are starting to bark up the right tree.

If there is an ignition module or circuit board on the furnace, posting the make and model number would be helpful.


I'd measure the voltage being applied across the motor windings that are being used by the furnace. If 120VAC are being applied to the motor and it not operating, that suggests a bad motor. If there is no 120VAC being applied then you'd look for a bad fan switch or a circuit board that's failing to turn on the furnace.
 
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Old 01-17-09, 02:18 PM
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Originally Posted by JLawrence08648
The furnace runs for 1 minute and then turns off for 5 minutes very consistently. ........, then the burner tubes light, this runs for one minute, then shuts off. During this whole time, the blower fan below does not go on.
You need to find why flame shutting down after 1 minute. A furnace would take longer than that to high limit, even if the blower was shot and never came on. The 5 minute off time (possibly)allows the exchanger to cool down enough so that for the next one minute sequence of fire, the heat exchanger never gets hot enough to kick the fan on.

It COULD potentially high limit after repeated sequences IF the exchanger were NOT cooling adequately by itself in 5 minutes. But not after the 1st 2 or 3 test runs. If flame goes out, then you have some other reason besides blower, as to why the flame goes out.

You need to find out why the flame goes off after 1 minute. There are various causes.

BTW, my own furnace, as do many others, can take about 1 1/2 minutes before heat exchanger temp allows the fan to even come on, at say a setting of 110 degrees, which is far short of say a 180-200 degree high limit that would obviously take more time to get to that temp.
 
 

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