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Old 01-24-2009, 12:20 PM   #1
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Burners quit during heat cycle


I am not familiar with furnace repair so I hope someone can shed some light on this problem. I have a Tempstar forced air furnace (T9MPV125L20A2 to be exact) that is only about 5 yrs old. The problem I am experiencing is the burners seem to shut off part way through a heat cycle keeping the house at about 60-65 degrees when I have the thermostat set at 68. I live in Michigan so it has been pretty cold here lately.

I took the front panel off to observe the sequence of the problem. After initiating the heat cycle, start-up seems normal. After a few minutes of burn, the burners shut off. The igniter will re-ignite the burners but they will only burn for a few seconds and then shut off again. Sometimes everything will re-ignite again only to shut off after a few seconds again. Then the igniter will make several attempts to re-light the burners but they won't re-ignite. Then everything seems to shut down even though heat is still being called for.

The valve is a Honeywell SV9541. When this occurs, it flashes 8 flashes indicating "High Pressure Switch closed when should be open". WHen everthing shuts down, it flashes 6 +1 indicating "Soft lockout - maximum retry count exceeded".

I tried cleaning out any possible obstructions in the tubes on the pressure switch, but this did not seem to fix the problem. Not sure where to look next.

Any ideas?

Thanks to anyone who takes the time to reply.

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Old 01-24-2009, 01:12 PM   #2
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Burners quit during heat cycle


your pressure switch is bouncing the main gas burners....things to check(unit toggled off) make sure the squirrel cage on the induced draft is clean and clear.....the tube(s) you checked blow into them check the connections to the ID duct..........the switch itself the 2 wires have to make(close)when the ID starts this proofs to the main gas valve that the air is going into the burner might have some moisture/water in it.with the tube connected to it you lightly blow into the tube you should hear a CLICK.repeat that just to make sure it is active.if you have an adjusting screw on the pressure switch (note its position)then turn it all the way in and all the way out and put it back to the original position.if you want to just heat the house up for now take the 2 wires on that pressure switch and wire nut them togeather and toggle up the furnace with the stat calling....as long as that ID is clear and not retricted you have heat.the reason there might be moisture in,and around the tube it is bringing in cold air and it condensates as it forces it down and thru the burner chamber.it is very important here that you understand the connection of that switch and its sensing tube in controlling the main gas burner.might want to change the pressure switch but for now let it dry out...get back with the fix/results here when you can

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Old 01-24-2009, 02:32 PM   #3
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Burners quit during heat cycle


thanks biggles for your reply. I did blow through the tubes and the switch did "click", so they don't seem to be seized up. After I re-connected the tubes and started the heating cycle, it seemed that the burners burned longer than before (about 8 min), the same shut-down occured and the valve gave the same error codes.

Maybe I might need a new pressure switch???

Thanks again,

Kent
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Old 01-24-2009, 02:50 PM   #4
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Burners quit during heat cycle


the reason i need you to connect the 2 wires from the pressure switch is to prove that it is the switch.if you get a consistant burn thats the problem......if you still go on off on the main burner it is something else!turn the adjuster out(2)1/4 CCW turns you will lessen the proof pressure from the tube,and get a consistant burner.to test the burner saftey while running(heating) PULL the tube it(burner)should shut down.....you just simulated the ID stopping during a normal heating cycle as designed.keep doing 1/4 turns out CCW till you get a solid run.

Last edited by biggles; 01-24-2009 at 02:53 PM.
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Old 01-24-2009, 03:29 PM   #5
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Burners quit during heat cycle


I don't recommend adjusting or bypassing pressure switches, except for testing purposes. Adjusting or bypassing the switch defeats the purpose of the switch. It is designed to prove unobstructed venting.
If the furnace fires and shuts down after a short run the pressure switch is probably working correctly. If this is a high efficiency furnace (PVC venting) you should check the condensate drain and trap for proper drainage. Also check the intake pipe for frost forming where it enters the home. Have also had tons of problems with those smart valves (gas valve). Bypassing or adjusting safety devices could cause problems to your furnace or your health.
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