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Old 08-08-2010, 08:02 PM   #1
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Powervent water heater woes

I have a GSW direct vent water tank that has been operating flawlessly since installed new 2 yrs ago. Yesterday, it shut down, codes indicating a pressure problem. I removed the flue (2 inch PVC, about a 13 ft run with 3 elbows) and tank worked again. No problem, I thought, blockage in the flue. I took it all apart and attached it back. Same problem. Took apart the blower motor, cleaned all the fins, ran a wire through the pressure switch port, tested the pressure switch and all looked ok. Hooked up 1/2 the flue, with all the elbows, tank still worked ok. Hooked up the other 1/2 exhausting to the outside, and it quit again. The second half is about 6 ft of pvc with a 45 degree on the exhaust end, with no rodent screen.
I notice that with the inducer motor running, there really doesn't seem to be a lot of suction, ie a glop of spit on the end doesn't really get sucked in. but obviously it's enough because the pressure switch operates until the second half of the flue is hooked up.I did verify the pressure with a manometer, the vacuum is about 1" with the flue off, and about .1 " with the flue on (the pressure switch activates at .15) hence it works without the flue.Exhaust flue specs state it is good for 50 ft, I calculate mine to be 31' with the elbows. Could it be the venting motor??It seems to spin good, spins for another 20 seconds after power is disconnected.
Today I decided to replace the flue anyway, stuck in 2 45 degree elbows and 10 ' of flue, , same result. The speed of the motor seems fine, and it continues to spin for at least 20 seconds after power is disconnected, so there does not seem to be any drag. Any chance anyone knows what the normal vacuum is supposed to be on the pressure switch port? The pressure switch tests out fine,(metered it)and it works with the flue off. I looked at increasing the diameter of the flue, but like I stated earlier, I have shortened up the flue to about 20 equivalent feet (according to manual 45 deg adds 3 ft). I think I just might bite the bullet and pick up a new motor tomorrow. Any thoughts???


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Old 08-08-2010, 08:13 PM   #2
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Usually if it trips at .15 you should have at least another .1 = .25 when working properly. On a furnace as much as an additional .5. The motor may be slowing down or there is internal restriction inside the tank. Rusty or sooted up baffles. Broken or missing orifice/baffle under where the ventor attaches to the tank. Do you have a negative pressure in the basement? Try open a window and see if it works. Go online and see if there is an exploded view of the internals/service manual for it.


"Cut it twice and it is still too short".

Last edited by yuri; 08-08-2010 at 08:25 PM.
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Old 08-08-2010, 09:31 PM   #3
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Check for obstruction around the burners air intake.
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Old 08-10-2010, 09:05 PM   #4
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replaced inducer motor, tested it, 2 " without flue, .3 " with, tripped pressure switch, all is ok now.
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