No sustained flame

Problems related to residential installations.

No sustained flame

Postby rodder » Tue May 17, 2011 8:22 pm

The furnace - Comfort Maker (Super High Efficiency) Model GUH 100 A016 CIN (16 yrs old), Module - White-Rogers 50A55-843 (2 weeks old), Stat - White-Rogers 1F56W-361, Filter - 16x25x4 (2 wks old). This is the 3rd module, original replaced after 14 yrs and replaced again 2 yrs later.
Issue - When stat calls for heat, inducer motor comes on, 20 secs later ignitor comes on and within 10 secs gas valve opens, nice blue flame last 1 sec on goes off (valve closes). Inducer motor stays on for a total of 60 secs, which is 30 secs after the blue flame. Inducer motor shuts off for 5 secs and the cycle is repeated. Continuous flashing of LED is described as Flame sensed >5 secs without gas valve. But I did get flames. Removed flame sensor from above one of the burners, cleaned it with emery cloth and reinstalled. Powered up the main switch and the same events were repeated. Is there a way to check the flame sensor? Thank you in advance.
rodder
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- No sustained flame

Postby 4ftBanger » Sat May 21, 2011 9:13 pm

Flame sensor works on a principle of flame rectification... Very simply - The flame will carry an electric current, but only in one direction so, in effect, it converts the ac millivolt flame sensor current into a dc current that is detected through the grounding of the board.

Based on your symptoms I'd be looking very closely at the grounding of the equipment and the condition of the metal parts. Rust around the flame sensor mounting bracket, burner mounts or cabinet parts can reduce conductivity and impede the flame sensor circuit. - Same goes for if the furnace isn't properly earth-grounded back to the breaker panel and subsequently to a proper grounding for the house.

(One of the toughest diagnoses i've ever had was a house where a brass water valve was replaced with a PVC valve and the electric panel was grounded to the water line. The PVC valve insulated effectively and broke the ground connection to the panel, resulting in many issues with the furnace and some GFI's in the house. Took us 4 trips to figure it out.)

Aside from grounding you may just be a victim of another ignition module failure. As the technology advances, the controls companies turn their focus on the "newest and best" while last years technology is handed down to foreign manufacturers to reduce costs. I've found that many replacement controls for some of the top manufacturers are marked "Made In ..." Mexico, China, or others, while the original parts are clearly marked "Made In USA" - I don't necessarily think they are inferior on the whole, but their track record seems to indicate that their quality control sometimes isn't as good.
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- No sustained flame

Postby rodder » Sun May 22, 2011 8:56 pm

Just happens I replaced the flame sensor 2 days ago and was going to wait a few cycles before I report. So far the system have worked as expected since the new sensor was installed. No codes, no run on of the blower motor and flame stays on to heat the house. It's been warm enough overnight so the heat demand is no longer needed. If I were to add a ground to the sensor, should I run a wire from the sensor retaining screw to a known clean ground on the housing? What about the same spot the Ignition Module is grounded?
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- No sustained flame

Postby alewicki81 » Sun May 22, 2011 9:48 pm

A ground from the house to anywhere on the unit should work. The flame rod can be checked in series with dc microamps. Your multi meter has to be equipped with it. A solid flame is between .8 AND 1.2 microamps. Anything below will cause problems. The range varies on some units.Check the manual or sometimes its on the control board.
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