Help me stop throwing money at this water heater!


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Old 02-13-12, 12:19 PM
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Help me stop throwing money at this water heater!

I have a power vent NG WH (50 gal Rheem) that frequently does not light. By "frequently" I mean about once each day or 2. Often enough to be a problem but not often enough for it to repeat when I'm trying to troubleshoot it
It ALWAYS works correctly when I cycle the power. Doesn't matter if I do this with meters & jumpers all over the place or not--it just works fine while I'm in front of it.

Years ago the ignitor relay went intermittant so I replaced the control box. When I realized it was a $7 relay to blame I replaced that relay & kept the old control as a spare. When this problem resurfaced I figured it was another burnt relay so I swapped the control. Worked for a couple days, then cold water again. Ignitor glows bright red but I thought maybe it's just going out of spec enough to not allow the gas valve to open so I replaced the ignitor. Cold water later that night.

This heater is 12-15 years old but other than this there's no reason to haul it to the landfill.
WHAT else might be the cause of this problem? How can I find out for sure? I hate the "shotgun" approach and want to replace just what is bad.
 
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Old 02-13-12, 02:06 PM
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What is the make of the gas valve on the unit?

Have you changed the flame sensor and or made shure its positioned properly in the burner flame?

Mike NJ
 
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Old 02-13-12, 05:44 PM
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Well there isn't a "normal" sensor. Apparently the HSI acts as sensor since it's the only thing in the flame:

[IMG][/IMG]

The gas valve is a RobertShaw 7200der:

[IMG][/IMG]

I wish I knew if the problem is that the gas doesn't light, goes out immediately, or valve never even opens but it won't misbehave while I'm watching it
 
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Old 02-13-12, 06:46 PM
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Thats a commercial unit, correct. There are varous tests need to be done. It really helps if you can get a manual for it. I have not looked for one on the internet.

Whats the exact model#?

Gas valve not even opening would be a fan or pressure switch issue. Going out within 3 seconds of it lighting sounds like flame sensor. ( Yes it a igniter and flame sensor )

You need to test these devices with a multimeter and monometer. Gas pressures, resistance, proper voltage, cfm ...ect.

The schematic on the door there should be your best friend....

Also those doors for the burner need to be on when operated. Sometimes a draft pulls the burner flameaway from the sensor with them off and the units go out as you describe.

Or if it only workes with the doors on it could be a make up air issue.

I worked on one like that in a chicken holiday. The thing was so coated in a coat of grease is no wonder the thing did not catch on fire....LOL.

I mean inside and out. Thick grease. Same in a chinese restaurant we serviced.

Ended up with sealed combustion units that take air from the outside.



Mike NJ
 
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Old 02-13-12, 07:53 PM
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WH is a Rheem 21VP50-1

Am I correct that the HSI doubles as flame sensor?
 
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Old 02-13-12, 08:30 PM
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Am I correct that the HSI doubles as flame sensor?

Yes .....................................
 
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Old 02-14-12, 06:59 AM
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Yesterday I tried a couple times to initiate heating by running hot water into the utility sink till the inducer motor turned on. The gas always lit. On my last attempt, after it was lit I pulled off the hose connection to the the inducer to get the gas valve to drop out (rather than my usual cycling the power). The gas stopped & the inducer kept running. I reattached the hose & the control box clicked & the ignitor glowed...but the gas valve didn't open. The ignitor turned off & after a few seconds turned on again. It did this a few times. I didn't know it had a "re-try" mode. After 3 attempts (I think), the inducer kept running but the controller didn't try to light the ignitor. When it screws up (when I'm NOT watching), this is how I find it--inducer running & no attempt to light.

Anyways for me the interesting part is the hose attachment to the inducer was a little loose & easy to pull off. In past troubleshooting attempts I jumpered out the sail switch (no change) but now that I know the controller quits trying after 3 attempts, this wouldn't make any difference & was no use in determining if the sail switch was bad. Possibly this loose connection was leaking enough to sometimes prevent the gas valve from opening. The sail switch is in series with the gas valve so it has no effect on the operation of the inducer or controller/ignitor.

I put a ziptie on the hose & will wait & see if the problem returns.
 
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Old 02-14-12, 07:19 AM
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When it screws up (when I'm NOT watching), this is how I find it--inducer running & no attempt to light.



Its going into lock out mode. after 3 failed attempts. The fan on is a saftey feature to expell CO, or gas for that matter on failure.

That is an older unit and there are no light to offer a trouble shooting code.

Do you have the manual?

Like I said you need to test some things. A lot of older power vents the inducer fan gets weak and it does not have the CFM to pull the pressure switch in constantly.

The fan running sounds like that type of issue from my experience. Usually when I walked in homes and the unit was just sitting there with the fan running the usual suspect was fan/pressure switch/vent related.

Mike NJ
 
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Old 02-14-12, 02:09 PM
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If it's not the loose hose (time will tell) then I do hope it's the fan or sail switch because I have spares. Several years ago a neighbor tossed an identical unit & I stripped the easy parts off it.
 
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Old 11-02-14, 11:18 AM
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Hi,

I have the same problem with my 21vp50e-1 Rheem WH. I also found the hose on the inducer very loose, at the end of the barb and easy to pull off. I tried the ziptye fix too. Did this resolve your problem ? It's never this easy for me though. Usually end throwing money at it too.

Thanks
 
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Old 11-02-14, 01:46 PM
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Sarah please start a new thread.... Thanks and welcome to the forums....

This thread is old. Closed!!!
 
 

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