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Thread: Water heater pilot goes out when furnace starts

  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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    Default

    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

  7. #7
    Master Plumber master plumber mark's Avatar
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    Talking master plumber mark

    what brand of water heater is it anyway. ???

    The new A>O>Smiths have been having a problem with 90% efficient furnaces doing this....

    But, before you get too involved in this, its wise just to call the local GAS COMPANY

    occasionally we see an old meter that simply needs a little
    WD-40 sprayed on it...
    actually they just come out change your meter FOR FREE because its is
    not working correctly for whatever reason, moisture--rusty and old inside ect...

    ask the gas company to change your meter first.....start with them before you drive yourself crazy.

    good luck...

  8. #8

    Default WH leaking too

    I started this thread. No solution yet, but I have confirmed that the water heater is leaking water. It has been off for days and half an hour after I have dryed the floor it is wet again, no doubt it is the water heater.

    I think I will install a force vented water heater with no pilot. But am also considering a tankless vented heater, Takagi.

    I have another question, how far from the furnace PVC vents must I go to put the WH vent. I don't have much room. The furnace has two 2" pvc pipes, the new water heater is 40,000 btu and I think I can also use 2" pipes. I would like to exit the house such that there is 2" clearance between each of the 3 pipes, all on the same horizontal plane.
    Last edited by BillMorehead; 02-15-2005 at 09:37 AM. Reason: mistake in text

  9. #9
    In the Trades Gary Swart's Avatar
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    Default

    I have a power vent water heater and a high effeciency gas furnace, both vented with ABS. They are several years old and require 4" pipe, but I believe newer models can use smaller diameter. Check the installation guide for the heater you want to install to make sure. I don't know of any restrictions on the proximity of the furnace vent and water heater vent, of course they must be separate. I have heard tankless heater can be inadquate if there are multiple demands at the same time, like clothes washer and shower. No personal experience however.

  10. #10
    In the Trades Gary Swart's Avatar
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    Default

    Should have added that the water heater has an electronic ignitor, no pilot light.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    There are some pretty specific instructions in the installation manuals for where you can place the vents from heaters, etc. One major restriction is the distance from things like the dryer vent. Assuming that it is a closed combustion system (i.e., it gets its combustion air from outside via pipe), most companies want the intake for the system 10' from a dryer vent. The chlorine from bleaches and othervapors can really mess up burners. Download the instruction manual, and compare it to that for your existing furnace.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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