I have not been able to keep my water heater pilot lit since I turned on my
AC. It might stay on for a day at most. The plumber suspected downdraft.
The Chimney sweep found nothing. When the heater is heating water there is
a powerful updraft through the chimney.
The sweep said I should have the thermostat replaced. I can light it ok, so
it must work somewhat. A previous poster suggested taking off the gas lines
from the valve and blowing them out, maybe that is next?
The downdraft is when the heater is NOT running. Air can get sucked down
Let him sweep the chimney, not fix gas appliances.
Blow them out? What do you expect to find in them aside from gas? If the
line was clogged so much that a pilot would not operate, surely the main
burner would be starved. It works when the AC is not running. Think about
the cause and effect of this.
Go back to the original problem again. The pilot goes out when the AC is
Does the AC affect the water heater thermostat? NO
Does the AC use the gas line in question? NO
Does the AC draw air from the same areas the water heater is in? YES
Does the blower cause a negative pressure in that area? Very POSSIBLE
Would a negative pressure cause a downdraft in the chimney? YES
Check that the return air ducts are functioning properly or if air is being
lost elsewhere to create the negative pressure in the AC area and thus, the
I just had another thought on this. Previously, someone mentioned watching
the pilot light when you have somebody turn on the blower. Good idea, but
carry this a step further. I mentioned negative pressure in the area of the
AC causing the down draft.
Watch the pilot light while the AC is turned on. After the blower gets up
to speed, have that person open a door upstairs. Opening the door will
allow air to leave the house while more is needed to feed the blower, thus
it may pull air down the water heater chimney. If there is a door to the
basement, close that while the upstairs entry door is opened.
Yes, and any fans that blow outside the house especially if its a newer
house. Dryer fan, kitchen stove fan, bathroom fan. Be sure fireplace
duct is closed if u have one. And on that front door thing, try opening
it with 'purpose' like you might when coming home from work. Maybe its
a quick gust thats blowing it out. I would expect if the door opens
inward it might suck air up the chimney and if it opens outward it might
suck air down the chimney.
For anyone who is still interested, the problem turned out to be my gas
valve. I turned off the AC for a few days during a cool spell and it made
no difference, the water heater pilot still went out. The plumber looked at
it for a long time and decided the valve was "bursting" the flame, which
blew out the pilot. AC is back on, everything is fixed.
I agree with Ed on this one. I will add that you did miss one thing
that might be part of the problem. You may want to try replacing out the
thermocouple. I wonder if you get some cold air in the area of the WH when
it is on? If the thermocouple is weak it could be the problem.
I once had a problem with a WH that no one could figure out.
Thermocouple was replaced several times, venting triple checked finally they
replaced the whole heater and no more problems. I never will know what was
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