Dayton Gas furnace, short cycles, Errors out "flame lost 5 times"

Old 02-10-16, 02:43 PM
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Smile Dayton Gas furnace, short cycles, Errors out "flame lost 5 times"

Hello and Thanks in advance for the help! I've compiled the details below based on what is traditionally asked for in similar threads.

Furnance is- Dayton model# FG9-UP, manufactured 2003.
2 story house, 2100 finished sqft, unfinished basement (800sqft)

Link to manual :

Observed furnace behavior-
* Stat is a 10 year old digital stat, stat is working correctly? I think.
1. Furnace call for heat occurs correctly
2. induction fan kicks in, 2-ish seconds igniter begins to glow.
3. 10ish sec later Gas valve clicks open, gas is sent to nozzles and flame ignites in the burners. Flame is a clean blue and consistent across all burners - stays that way the whole time.
4. Furnace operates properly for 1-3 minutes- burners lit, main fan active.
5. After 1-3 minutes, flame goes out - visually see flame dissappear and hear distinct sound of flames dissappear.
6. 1/4 sec later gas valve clicks ...closed I assume.
7. 10 sec later glow from igniter appears.
8. another 10 sec, click from gas valve and flames appear ...repeats step 5,6,7
four more times then errors out.

Main fan stays on after burners shut down.
9. Indicator light flashes 8 times which is the code indicating flame lost 5 times during operation (suggests faulty gas valve or low gas pressure).
Text from Manual: This fault is indicated if the flame is lost 5 times (4 recy-cles) during the heating cycle. This could be caused by low gas pres-sure or faulty gas valve.

10. Furnace stays in this state until auto reset from lockouts (1 hr) then starts the cycle over again. If I cycle power at the furnace it will restart immediately but usually errors out again (8 flashses) in 10 minutes or so.

I also saw a 6 flashes error: This indicates that after the unit was operating, the pres-sure switch opened 4 times during the call for heat. If the main blower isin a “Delay on” mode it will complete it, and any subsequent delay offperiod. The vent motor continues to operate until the pressure switchre-closes or a call for heat is removed.

Have not had serviced in past 10 years. Other than replacing filter and vacum out/around furnace.

Testing and trouble shooting I have done so far:
Inducer motor (plastic housing) leaks water, so I removed blockage in the drain (black calcium? stuff). water has not leaked onto control board, but bottom of furnace appear damp from water dripping.

I did flip the on'off switch on the gas valve during one of the cycles to see if the flame outage sounds/sequence was similar to step 5 above. duh ... it looked the same.

filters are clean and no obstructions

Have not cleaned the flame sensor. Have not inspected the high limit switch to see if that is the problem.

House temperature stays about 67 ...but expect a cold spell to make things miserable if this isn't fixed.

I frequently repair auto and electronics, Please recommend next steps. thanks.

Last edited by iowa_snow; 02-10-16 at 03:00 PM.
Old 02-10-16, 06:57 PM
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Internally clean all pressure switch connection points, rubber hoses and steel nipples. You may need a succession of sizes of small drill bits to properly clean the nipples, especially in the draft fan or combustion chamber sections. Post back with your results.
Old 02-11-16, 12:30 PM
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This diagnostic code suggests that the circuit board is intermittently failing to verify that the main burners are lit. When that happens, the main burner gas shuts off and the ignition cycle occurs again.

The most common cause of this problem is a dirty flame sensor that is coated with invisible oxides that accumulate when the flames strikes the flame sensor.

The flame sensor is typically a rod on the opposite side of the furnace from the hot surface ignitor, with a single wire going back to the circuit board.

The flame sensor is usually easily removed, and the oxides cleaned off with a wire brush or fine sand paper. You just need to clean the surface, not cut into the flame sensor metal.

Try that first.
Old 02-12-16, 07:18 AM
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=== Appear to have Fixed Problem: ===
I removed and reattached the rubber hoses linked to the pressure sensor, not having read your instructions to clean the steal nipples(I failed to consider that). One of the hoses seemed rather loose (I snugged it up farther onto the rims of the nipple). Considered attempting to clean the flame sensor but called it a night and turned it back on. The furnace furnace now runs to completion, no short cycles. However, I appreciate the advise to clean the flame sensor and will do that next.

Thanks for your advise and for the previous answer on the forum which helped to better understand the furnace operations and possible problems.

-- Remaining Concern ---
I am still concerned about the inducer motor leaking and will keep an eye on it. If it continues to leak, does it have to be replaced or is a small leak with limited residual water dripping ok? 13 yr old furnace... 5 yrs to end of life ?
Old 02-12-16, 09:30 AM
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duplicate ...deleted ... please ignore

Last edited by iowa_snow; 02-12-16 at 09:31 AM. Reason: Duplicate submission
Old 11-13-16, 11:18 AM
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First step that should not EVER be skipped is check the outlet duct on your inducer fan. Through the summer months that is a favorite spot for waspers to build nests and can cause some hard to interpret symptoms. There has been many a control board/flame sensor/pressure switch/gas valve etc replaced due to not doing the most basic steps first

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