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Old 01-05-2013, 06:26 AM   #16
MaineScoot OP
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Damn. It's still doing it. I'm heading over to Appliance Guru.
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Old 01-06-2013, 01:14 PM   #17
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flame sensor

Can you see the pilot flame ? it should be bright blue and fully engulf the tip of the thermocouple , if there is one .

Does your power vented water heater have a flame sensor , in addition to the thermocouple ?
If you inspect the connections between the burner and pilot assembly ( hidden in the bottom of the unit ) and the gas valve , you may see a thin wire , in addition to the pilot line ( 1/4 " dia aluminum tube ) , the main gas line to burner ( 1/2" dia aluminum tube ) , and the thermocouple ( 1/8 " dia copper solid wire ).
If so , the wire is for a flame sensor , which must be cleaned occasionally , by gently sanding the probe , located at the burner .Note - sanding a thermocouple does no good , they're cheap and easy to replace . A thermocouple creates electricity , approx 250 millivolts , by being engulfed in the pilot flame . A flame sensor conducts electricity when engulfed in flame , thereby proving that the flame is lit.
To clean the flame sensor , and/or replace the thermocouple ( might as well while you're in there ):
1) shut off gas to appliance . We don't want to read about you in the paper tomorrow .
2) disconnect all outputs from bottom of gas valve ( flare fitting for main and pilot lines , thermocouple , sensor wire , etc.)
3) remove burner from bottom of water heater
4) clean sensor , replace thermocouple
5)re-assembly is reverse- ensure burner is properly placed - scope it out with a flashlight as you reinsert burner , there's probably tabs to locate it.
6) turn on gas , relight burner and test all joints with soapy liquid for leaks .

As a licenced gas fitter , this would take me about 1/2 hour to do , and I'd charge $80.00 plus travel

Naturally , you accept full responsibility for your actions , if unsure , call a qualified technician .
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Old 01-06-2013, 01:44 PM   #18
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Beware the intake air lockout when messing with the burner. If your heater is new enough, it'll have a one-time-only safety on the intake air that once tripped, requires throwing away the whole heater. What trips it is a blowout from unburned gas igniting. Doesn't take much. BTDT.
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Old 01-06-2013, 02:00 PM   #19
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ok EDIT - shit sorry, im thinking gas furnace not water heater, never mind!~

is it lighting the burner at all? as in, does it light and then go out?
or just it just continually try to cycle without the gas valve ever opening? ( if there is a pilot light, it will light the gas burner when 24Vac is put to the gas valve)
it is the control modules job, to open the gas valve for usually 4 seconds, then wait for the flame sensor

flames sensed, gas valve stays open until thermostat is satisfied.

no flame sensed, gas valve closed, and cycle starts over

usually 3 cycles ( attempts to light) , with a 30-40 seconds purge ( fan on) in between until a lockout occurs.

after lockout, you will have to remove power from the control board for 45 seconds or so to reset it.
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mouthfulloflake screwed with this post 01-06-2013 at 02:11 PM
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Old 01-06-2013, 02:03 PM   #20
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Sure sounds like a pressure switch. I had something very similar with my furnace.

You need to determine the logic of the startup cycle and troubleshoot each component in order.

You can determine if the pressure switch is working by checking with an ohm meter.

My guess is that when the power vent kicks on, the pressure switch should close, and then gas valve open, and gas flows. Then a flame sensor would check to see if the unit lights within a few seconds, and if not, it will shut down and try to recycle.

If the pressure switch closes when the power vent kicks on, and the gas valve doesn't open, you've got a different problem.

Unfortunately, testing the control panel is difficult, if not impossible, other than swapping one out.

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Old 01-06-2013, 02:14 PM   #21
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As a lifelong state licensed plumber that spent his whole life installing and repairing steam and hot water systems I can tell you professionally that a water heater is the very most in-efficient way to heat a building using your radiant heating system. The efficiency rating is a small percent of what a boiler is made for that purpose. But water heaters are cheaper than boilers------just so you know.

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Old 01-07-2013, 10:06 AM   #22
MaineScoot OP
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Thanks for all these ideas. The annoying thing is if I go downstairs right now and turn on power to the unit it will start right up and run fine until everything is up to temp. It's only the next time it tries to turn on that it wont fire up. It just tries over and over.

Bigdog, I know that this water heater isn't as efficient as a real boiler. I'm just heating a 450 sf basement shop to about 50 degrees. If I have a big project going I might turn it up to 55 for a couple of days. I just didn't think I needed to spend 3 or 4 thousand dollars for a real boiler for this application. The whole thing has worked fine for over a decade.

So what I've been doing the last few weeks is to just turn it on and let the floor/room heat up then turn it off when I hear it failing to light. I will find time soon to go over the manual.
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Old 03-26-2014, 07:10 PM   #23
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Update: I limped through last winter just turning the water heater on once a week or so to warm up the slab. It would run for 6 or 8 hours then go into failure mode. So in October I called in a pro, the heating company that services our oil burner sent over their gas guy and he checked out the heater. He diagnosed the problem as a bad pressure switch. He said he would order one and be back in a week or so to put it in. A few weeks went by and no word. I called and they said they were having trouble finding the switch. And that's how it's gone all winter. They kept saying they could find it and they'd let me know. Until 2 weeks ago. That's when they told me they couldn't find the switch and I was on my own.
So I emailed the guy at State that sent me the service manual last winter and he said sorry, State won't support it but try So I contacted them and they said sure, no problem, we'll send it right out.
So I put it in last night and guess what? It's still doing the same thing. Doh! I'm back to square one.
Rereading this thread, and knowing it wasn't the pressure switch it must be the flame sensor. Right?
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Old 03-27-2014, 03:53 PM   #24
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Originally Posted by MaineScoot View Post
I'm back to square one.
Rereading this thread, and knowing it wasn't the pressure switch it must be the flame sensor. Right?
It could be, but it could also be a bad connection in the control and/or safety circuits, a bad gas control valve, or a bad control circuit board, or ??? You really need to read your service manual, and figure out the firing sequence. Then use a meter and check for the proper voltage at each component in the control and safety circuits, in sequence. Make sure all wire connections are clean and tight. It doesn't take much corrosion to block 24 Volt control voltage. It takes even less if it is a millivolt system. Or you can keep guessing and throwing parts at it till you get lucky and get the right one.

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That has been set to roam
Excels a dunce
That has stayed at home."
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Old 03-27-2014, 06:12 PM   #25
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MaineScoot, call the propane company and have them come out and change the outside regulator. I was having the same puzzling experience with my radiant heating system. It would start up and run for a while - shut off - start and run - shut off. Everything checked out fine, but it just would not run consistently. I did everything short of jackhammering up the slab to change the Pex to try and fix the problem. Two different plumbers couldn't figure out what was wrong.
Finally I called the propane company and they said I probably have water in the gas. They sent a service tech who removed the regulator, took it apart and showed me the inside which was frozen solid with ice. During the day as the sun warmed the regulator, the inside thawed and would allow enough gas to pass and fire the wall mount boiler. Later as the temperature fell, it would freeze and block the gas flow. The service tech said the propane delivery drivers are supposed to manually add methanol ( ? ) at each truck fill during the winter months to prevent freeze ups. But some times they forget.
New propane company and all is well !
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Old 03-27-2014, 10:12 PM   #26
MaineScoot OP
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Thanks, Walter. I'll have time to do that Saturday.

DH, it burns Natural Gas not Propane so I don't think it's a water issue. Plus the kitchen stove and the Rinnai in the apt over the garage are both burning fine.

The most frustrating thing is if I go downstairs right now and turn it on it will run fine until morning.
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Old 03-28-2014, 03:50 PM   #27
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try the wall.....
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Old 12-06-2014, 09:59 AM   #28
MaineScoot OP
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So here I am 2 years later and I never sorted out my heater issues. I thought I'd try one more time here before bringing in a pro again. Remember, that didn't go well last time. So here are a couple of pages from the manual:

I've replaced the pressure switch. It still does the same thing. I took a video last year, I'll try to find it. I feel like this thing is so simple that I should be able to figure it out.
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Old 12-06-2014, 12:56 PM   #29
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I saw your previous post about the pressure switch. It sounded like the problem.

When mine went bad on my furnace, a generic replacement from the local supply house fixed me up, and was a lot cheaper than the OEM.

If it were me, I'd start it from cold and carefully note the start cycle sequencing and what each component is doing. Then I'd lower the temp to let it shut off, turn the temp back up so it will try to restart, and note what doesn't happen correctly.

I'd think the cycle would be something like the the blower comes on and closes the pressure switch (you should be able to confirm the pressure switch closed with an ohm meter, or a test light) Then you should hear a click as the gas valve opens, and you should hear gas flowing. Then the main flame should light off the pilot. Or something like that.

But something is obviously not happening when it tries to relight that successfully happens when it lit the first time.

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Old 12-06-2014, 04:07 PM   #30
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Earlier in this thread, someone mentioned the offices on the draft inducer fan getting clogged. Check them again, they are tiny and clog easily.

Post a pic of the pressure switch its self. When the rubber tube is removed, is there a restrictior piece in the nipple on the switch?
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