Heater starts/stops several times then stops, then fan starts.


Old 12-04-04, 07:46 AM
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Heater starts/stops several times then stops, then fan starts.

My Rheem forced air / natural gas furnace will start (i.e. pilot glows, then gas ignites for several seconds, then stops ) two or three times. After the second or third try the fan kicks on and runs, but the furnace is not burning. I can hear when the furnace is getting the signal from the thermostat. I have tried leaving the thermostat in "fan on" and "fan auto". I have tried leaving the thermostat in a temperature hold. On occasion through the day, if I leave my thermostat at a holding temperature, and I can here the heater/fan kick on / off, it will actually start "working", but eventually goes back to "trying" to work but failing? Ahhh! help please. I don't know how to verify if it is the thermostat (honeywell ct3600) or the heater / fan. I also have central air controlled by the same thermostat. I have four wires, red/white/green/blue connected to r/w/g/y terminals respectively.
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Old 12-04-04, 08:04 AM
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Take and jump R to W and hold it . That should turn on the heat. If it does and stays on the whole time you jump R to W its in the tstat then. If not its down in the furnace the board or in the pilot light.If you turn it to fan on and the blower runs then the blower should be OK.

Old 12-04-04, 03:40 PM
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Chances are the ignitor isn't sensing flame.. You may need a new ignitor or board..
Old 12-05-04, 11:54 PM
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I just replaced a 15 year old Amana 90+ efficiency unit with a new Ruud (seems to be same as Rheem?) Achiever 90.

I had the same problem. Unit was installed 7 days ago.

Problem is that not all 5 burners will light. There is a flame sensor at the end of the burner assembly opposite the igniter. If the flame doesn't travel all the way down the burner assembly in time (seems to be ~5 seconds) the gas is shut off and the unit goes through a purge and relight cycle. If no light on the second cycle, it goes into 1 hr shutdown mode after a 3 minute cooldown of the heat exchanger (the main supply blower runs, pushing non-heated air throughout the house). All of this is detailed in the owners/installation manual which I have.

It does this intermittently, so the house stays +-1 degree of set point since it lights off on average at least once an hour. I have a tight and well insulated older house.

I believe the problem to be insufficient combustion air. The previous unit burned out one combustion air blower a year for the three years we've lived here, due to improper retrofit of a non-oem combustion air blower (apparently Amana had a problem with the original unit?) and improper condensate drain. After $1000+ in repairs we went for a new unit.

It will light reliably with the upper (gas burner) cover off but when the cover is installed, will fail in the described manner >50% of the time.

The original install of the previous Amana unit had 2" exhaust PVC and no intake. I am in the process of installing 3" intake and exhaust PVC per manufacturer specs. I am also trying to conform to specs for installing direct-vent (intake and exhaust with blower) water heater since that is coming within the next 6 months.

After looking at the mess, I am convinced that since day 1 of the Amana install (15+ years ago), the whole house has been negatively pressurized a little or a lot depending on time of year and use of the clothes dryer. The current water heater is an old-school atmospheric vent with pilot light.

My solution is going to be to replace the water heater ASAP with a direct-vent unit, and install an energy recovery vent in the next year.

I am also considering installing a fresh air intake line from outside to the furnace return air duct. I can't seem to find any specs on this either in the furnace installation manual or online. I found a reference to it on a couple of diy sites. This would help balance the house with outside, and condition/filter the air when the furnace is running. Any advice?
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