Hep me Wallies, Hep me.... (ME)

Mark Eatherton1

Gents, especially you flame heads from back East. I have a particullarly troublesome pair of boilers. They are Buderus G125/4 and are using Field remote mounted draft inducers.

They were installed by a now defunct mechanical contractor 2 years ago. They were originally set up with Riello power burner that we couldn't get to run right to save our souls. We replaced the Riellos with Carlin G3B natural gas burners which in the past have been simple to setup and run. Not this time...

I followed the installation manual to the T.

3-1/2" W.C. at the gas valve outlet, orifice derated for operation at altitude. Adjusted the air shutters to factory recommendations. Start the boilers and they immediately begin back firing through the gas/air inlet. Draft over fire is -.04" W.C., breach draft before draft regulator is -.04" W.C. I call the factory to find out W.T.F.O., and they ask me the combustion gas parameters. I tell them I've got the CO at 50 PPM (per the manual), excess air at around 50%, O2 at around 5%, CO2 at 8%. They tell me the reason is it back firing is because of the excess air being too high. I re-adjust the air shutters and take it down to 10 to 20 % per the tech rep. The CO2 jumps up to 10%, CO jumps to 100 PPM, 02 drops to below 3 percent. Try multiple start stops, system lights off smoothly. I buckle everything back up and leave, and the customer calls me the next morning to say that the boilers back fired everytime they tried to fire the night before. I sleep on it over night and decide that the draft inducers are creating way too much negative pressure over the fire. When I get to his house this morning, one of the draft dampers blade is laying on the floor and that boiler is running. The other, with the blade still intact is off line, locked out from failure to ignite. This confirms my suspicions about excess draft over the fire. Looking further into things, I find that there is an adjustable damper on the Field inducer that allows the installer to lower the negative pressure created by the inducer. I crawl WAY back into the crawls space and find the dampers have never been adjusted from their original 100% open settings. I adjust both of them to 50% closed, CRAWL back out to the mechancial room and check my over fire draft. It dropped .01". I double check all the other combustion parameters and make sure that nothing has been adversely affected. Everything is fine. I start and stop and start the boilers (both of them) probably 20 times, including cold start, hot restart and so on and so forth. Everything lights off nice and smooth. I leave. Before I get home, the HO calls me on my cell phone and tells me it happened again.

I'm nearing my wits end. Is it the excess over fire draft ?

I'm going back tomorrow with an assistant that can crawl back into the crawl space and adjusting the inducers to
-.02" W.C. pressure and resetting all the parameters.

Any suggestions??

TIA

ME

bill clinton_3

back fire

Me: I'm far from an expert on power burners and remote power vents, so don't laugh at me too hard if I say something stupid. Had just one somewhat similar experience with a similar setup: Control would light up the burner; it would run for 30 seconds to a minute; then it would shutdown and recycle. I just couldn't believe the flame had any way of knowing what the pressure above it was relative to ambient. Once the CO2, O2, CO levels are right, you should be able to have good ignition with minus ten feet over the fire draft--air flow is what matters, not pressure: the requirement for over the fire draft is just to make sure you got enough draft to clear out products of combustion. Nonetheless, we set about reducing that draft with the baffle on the exhaust fan. Made no difference. The problem was the differential pressure switch in the exhaust fan. Now, when you walk in the boiler room, you still risk getting the shirt sucked off your back and into the barometric damper, but the boiler runs fine and all readings are to spec.

My point is I think you're letting that high draft spook you. I think you're getting delayed ignition for some other reason and that it's in the control or the wiring.

Okay, I tried; be nice to me.

Bill

Kevinj

Gas pressure

Have you watched the manometer to be sure that on light off that the supply gas stays above 6" ??? I like a monometer on the supply line and one on the maniflod for this type of problem. A dip in supply pressure at valve opening can cause problems.

bigugh_4

Gas pressure!

tricky stuff, Causes a lot of kinky problems. Main regulator at the meter. Make sure it is ok. Have the Gas Co check it. Make sure the atmospheric side of the diaphragm is open to the air. Little spiders can and do plug that opening. The unit regulator, same thing . Like Kevin said, check in both places, supply in and manifold out.

Mad Dog

Mark , give me a call on cell phone, Monday,

Jimmy, whom you spoke to the other day is THE MAn in that category. Gimme a call. Matt

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John Ruhnke1

Draft and air pressure

Mark,

Look for negetive pressure building up in the building basement. It sounds like air from the outside is moving backwards through to the burners. It produces flame rollout. The flame actually comes backwards through the air inlet in the burners. Look for closed doors, fans running, improper room combustion air. Sometimes funny things happenn, like hot air running up into the attic and creating negitive pressure in the basement through some open vent or even a future plumbing stack. Hot air rising will cause negative pressures at the basement. If the boiler room goes negative you will get back fireing, or flame roll out.

John Ruhnke
JR@ComfortableHeat.com

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