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Question DetailsAsked on 12/12/2016

Why won't my gas furnace burners come on and it sounds like there is water in the system

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2 Answers



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Answered 3 years ago by Member Services


Could well be, if a high-efficiency unit (direct vent out wall through plastic pipe, as opposed to up to the roof through metal vent pipe). Because that type of high-efficiency unit runs low exhaust temperature and uses a blower fan to exhaust the combustion gases, the water vapor (which is a significant portion of the exhaust gases) can condense in the exhaust pipe (especially at cold outside temps) or frost up at the outlet, forming water in the pipe. The building codes in many areas aggravate this by mandating an upward 90 on the outlet pipe - which catches precipitation and also prevents drainage. (Smarter area require a T on the outlet and a downward slope on the flue pipe so the water will drain out to the ground).

Anyway, on most such systems, there are one or two plastic drain tubes from the exhaust flue leading down to a drain or catch trough or cup, usually mounted on the outside of the furnace. if these tubes get clogged up, water can build up in the flue and gurgle as the air moves it around trying to expel it (which it normally cannot do because the exhaust fan is very weak - just enough to move the exhaust gases along). Eventually the water builds up enough to trigger the backpressure sensor (as sounds like it did in your case), or runs down into and damages the furnace, or gets in the exhaust blower and shorts it out, causing furnace failulre to start or sometimes will start and fire for a few seconds then shut down when it detects that the exhaust gases are not being exhausted by the fan.

Usually the tubes are easy to pull off (may or may not be clamped on) and run water through to ensure they are free draining, and use long pipe cleaners to clean out any builtup sediment or minerals. If significant buildup, undiluted kitchen vinegar can help clean them out.

One other possible cause of this at times - main blower unit is dust-laden and dragging inside its housing, causing a sound similar to bubbling water - though in that case usually it would kick on OK, just maybe shut down shortly after due to overheating.

Note - there also pressure sensors with tubes attached to them as well - so pull out or go to manufacturer's website to download the owners and maintenance manual - should label the drain tubes on the diagram, and may also give maintenance instructions in the troubleshooting guide.

Answered 3 years ago by LCD

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