Gas water heater help

I have a ten year old gas water heater, a State Select 40 gallon PR640NOVT. I use it to heat my workshop. So it was turned off for the summer. When I turned it on and lit the pilot a few weeks ago it ran fine at first but the next day when I was in the shop I noticed it was trying to fire up but couldn't. The power vent would come on for a couple of seconds but the burner didn't light and it shut down. Then it would try to fire up again... Repeat.
So I turned it off but a week later turned it on and it fired right up. Later I noticed it wasn't firing up again. I guess it is some kind of safety switch malfunctioning, what do you think?
The pilot stays lit, what should I check/replace first?

replace the thermocouple

The one down by the pilot light? I think that is fine, if it were bad the pilot wouldn't stay lit.

Water heater to heat the workshop? How does that work? Like cirulation to a heat register?

Anyway, I assume the main burner is not coming on? It has a power vent too? I'd make sure all the things are working in the order that they are supposed to. You can try and clean the thermocouple first with sand paper.

+1 on sanding the thermocouple. Its job is to sense the main burner, if it is dirty/damaged, it won't signal the main valve to open.

Also, how is the gas supply line coming to the unit? Often, air will get into the system and can be a SOB to purge. Until it is purged, it will work like you describe. Run, then die and not refire.
I've also had spider webs up in the burners in units that sat unused for a spell. Get some compressed air and clean out the cobwebs.

Keep us posted.

There is a circulator pumping the hot water through three 200' loops of hepex (cross linked polyethylene) buried in the concrete floor. There is a radiant barrier under the concrete.


So are there two thermocouples? One for the pilot light and another for the main burner?
The gas supply is good or the pilot wouldn't stay lit.

On gas appliances with power vents, the unit wants proof that the power vent is sucking a vacuum before it lets the main burner come on. Some place on the vent fan housing,there should be a flexible hose of maybe 1/8 to1/4 of an inch. This hose will go to a vacuum switch that allows the main burner to come on. First,check the hose for cracks where it fits over the barb fitting. Then check the barb fitting itself. I have seen them get crudded up with dirt and deposits. A little drill bit turned in your fingers usually will clear them. Spiders love the 'gas smell' and will build little blockages in dormant gas appliances. You can also check the vacuum switch with a continuity tester to see if it works if all else fails. Make sure that the discharge pipe or chimney is not plugged as well
Any time I have had problems,a cleaning solves them with no parts needing replaced. Hope this helps, and please tell us how it goes for you.

hmmmm... if there is a pilot light that is usually the lockout, but I know on other types of burners there is a sensor that looks for the main heat... you may or may not have that. anyway, when the start cycle begins, the burner fires maybe 10 -15 seconds... if the sensor does not detect heat, it shuts the main gas off because it thinks the main did not light. is that what you have?

otherwise the last post on the power vent is pretty right on...thats where I would look

+1

Air intake clogged? My home furnace locks out whenever I get snow accumulated in the intake vent. Doesn't take much, but I guess it senses the minor vacuum and locks out.

Post up a picture of your water heater if you could.

I am not sure but it sounds to me like it could be either the flame sensor is corroded (fire conducts some electricity) or the pressure switch is not working (which could be bad draft motor or bad switch).

-John

Thanks, you guys. I think it must be the pressure switch. I emailed State but haven't heard back from them. I will give them a call. I disconnected the tube that runs into the power vent and cleaned it out with a pipecleaner. But it's still doing the same thing. It's annoying that it runs fine if I turn it on cold. And runs fine until it's up to temp. But the next time it calls for heat it hangs up.

Are you using Propane ? I had the same problem in my shop. Wall mount boiler. Start up fine, then shut down. Went round and round trying to figure it out. Someone mentioned water in the propane. Called the gas company, they came out and replaced the regulator on the side of the barn , low pressure regulator. They opened the regulator after removal and it was frozen solid with ice. Enough gas would push by overnight to fire in the morning , but not enough flow to maintain burn. Propane company driver told me they need to add methanol ( ? ) each load to prevent freezing in the winter. Some drivers can't be bothered. Changed the Propane supplier and all is fine for the last 6 years.

Mmmmm - hot H2O heat in the floor - my favorite!

I have had good luck finding water heater and other appliance repair ideas on

http://applianceguru.com/forum26/23724.html

Let us know what the problem turns out to be.

I talked to a nice guy at State today. He was able to send me a PDF of the correct service manual. I found the pressure switch and cleaned the other end of the hose. And I tapped on the regulator like he told me. I think it's doing ok. I'll keep an eye on it. They had tried to email me earlier but got one letter wrong on the address.

Damn. It's still doing it. I'm heading over to Appliance Guru.

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 .

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.

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.

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.