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Thread: Water heater pilot goes out when furnace starts

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  1. #1

    Default Water heater pilot goes out when furnace starts

    My water heater pilot goes out very often in cold weather. It appears to be caused by momentary gas pressure drops. I am asking for comments for an action plan.

    Today I setup my video cam toward the pilot and have learned that it goes out when my Lennox pulse furnace starts up. Sometimes the pilot just gets real low for a second and recovers, sometimes it goes out. It acts like a gas pressure drop when the furnace starts. During my video recording I had the water heater in pilot mode so it wouldn't start heating. I also put a short wax candle near the burners for light and to evaluate if a draft was the culprit. The candle did not flicker when the pilot went out.

    I had been thinking I needed to replace the water heater but now that I have linked the problem to what seems to be gas pressure, I donít know what action to take.

    My natural gas supply is a higher pressure than normal residential service. Just before the meter there is a 2 PSIG regulator, after the meter the 2 PSIG supplies two in-house downstream lines. One goes to a .5 PSIG regulator that feeds the water heater and the Lennox furnace. The other 2 PSIG line continues to other appliances (range, dryer, 2 tankless water heaters) with additional .5 regulators near those appliances. The upgrade to 2 PSIG took place 3 years ago and seems to have been working okay in past Wisconsin winters.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default pilot

    .5 psi is too high for the units unless the control valves also have regulators to reduce it to about 4-5 inches water column, which is about .2 psi. Either the burner coming on is creating a surge which blows the pilot out, which could be the most likely problem, or the regulator is causing a momentary drop that puts the pilot out. A second regulator for one of the two devices should cure the problem.

  3. #3

    Default

    I don't think it could be a surge blowing out the flame. While I was observing the pilot going out, the water heater was in "pilot" mode. There was no flicker on the candle that I had 3" away from the pilot when the pilot went out.

    The water heater is a Ruud T50. Is there a regulator on these units?

    The regulator that feeds this line says 7"-11", and it feeds the water heater and the Lennox pulse furnace.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default pilot

    A surge in the gas pressure would have absolutely no effect on a candle, even if it were next to the pilot burner. The heater pilot is designed for 5"-7" w.c. When the furnace start and the regulator opens, it can momentarily open further until it stabilizes and the extra pressure can "blow" the pilot out. Some gas valves regulate the burner pressure but not the pilot, and I do not know if your valve is one of them.

  5. #5
    Plumber jimbo's Avatar
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    I agree that the problem is gas pressure. Most gas WH, the control valve is also a regulator. The only way to diagnose the exact problem is to get pressure gauge teed in to see what is happening to the inlet pressure at the WH, and then if necessary the outlet pressure at the pilot.

    These gages can be pricey, although I have seen some reasonably priced units. Look at www.********.com item #150242, $47. Measures 0-20 oz/ 0-35".

  6. #6

    Default Gas pressure too low?

    We just went through my neighbor hood with a similar problem. The gas company found water in out lines that caused "LOW" pressure. No one could run the furnace and water heater together until they resolved the problem by removing the water

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