LP Appliances- pilot type water heaters
In my last blog entry, I touched on the theory behind using a pilot and thermocouple as a flame safety device in an LP appliance. This week we’ll look at how it works in the most common RV application- an LP water heater.
The 2 main RV water heater manufacturers are Atwood Mobile Systems and Suburban Manufacturing. I’ll look at an Atwood model (because that’s what I have on the lot to photograph!), but the problems, fixes and maintenance are largely the same for both manufacturers.
The main parts in a pilot type water heater are the gas valve- which performs a dual duty- as a thermostat, maintaining the desired water temperature, and as a safety valve, shutting off the flow of LP gas when the pilot is out, the manifold and orifice (the manifold is the brass part right under the gas valve), the burner tube, and the pilot assembly (of course, the tank and all of the case are also important!)
In the picture to the right, you can see the probe which is inserted in to the water heater tank to sense the temperature of the water. On this particular valve, the temperature is set by a lever on the top- other models use a knob on the front for temperature adjustment. LP gas enters the valve, goes through the safety valve assembly, then goes through the thermostatically controlled main valve, then out to the orifice and main burner.
You can see from this picture the electrical connection I talked about last week- the current from the thermocouple has to go through the wires, which lead to a thermal fuse, also known as an “ECO” or Energy Cut Off” fuse. This fuse will blow when the water temperature reaches an unsafe level, interrupting the flow of gas to the main burner and pilot, shutting the water heater off. If this fuse is bad, the valve must be replaced. Another type of failure is when the thermostat valve doesn’t shut completely off, leaving a small flame burning at the orifice- again, it’s time for a new valve.
Next we come to the main burner assembly. Even though the pressure of the LP gas is very low, when it comes out of the orifice and enters the burner tube, the flow is enough that it pulls air in to burn. LP gas has a fairly small range of air to fuel that it burns well in- this adjustment allows you to fine tune the air mixture. There is a similar arrangement (though not adjustable) for the pilot assembly.
If the main burner adjustment is off, the burner is dirty (even by a spider web), or the pilot air inlet is dirty, the result will be incomplete combustion- a yellow flame and soot buildup.
To clean and adjust the main burner, a burner tube cleaning brush can be used- slide the “air shutter” open, run the brush through, and readjust the shutter. To adjust the shutter (air mixture), I like to slide the shutter closed until the flame is yellow and “lazy”, the slide it open [b]just[/b] until the flame starts to roar. On Suburban models, the flame is supposed to roar (but is non-adjustable), on Atwood models, it isn’t.
One last look at a pilot assembly- here you can see the tube, the orifice and the burner. It’s worth noting that the orifice is replaceable, though often it is better to simply replace the whole assembly (getting a new thermocouple is the proccess).
If the pilot flame is burning yellow, it is usually enough to simply blow out the assembly, by applying compressed air to the air inlet hole- 90% of the time, this will clean the assembly well enough to get rid of the problem
So- the problems with a pilot type water heater can be:
Pilot won’t stay lit:
- Too small a pilot flame (clean)
- Bad thermocouple (replace)
- Bad gas valve (replace)
Burns, but creates black soot:
- Dirty/Blocked Burner Tube (Clean)
- Dirty Orifice (have cleaned by qualified person)
- Bad LP pressure (have set by qualified person)
I hope this touches on the main causes of the dreaded “cold shower” when using a pilot type water heater.
Questions? Comments? Discuss in this RV.net forum thread.
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Great post. I have been experiencing black soot. Now I know why. Any tips on cleaning the Orifice myself? I’d imagine that would be a tough job but I am curious. Thanks again!
Hi Rick,
99% of the time, soot will be caused by the burner tube needing cleaning- even though I will usually clean the orifice if I’m servicing a water heater, I can only think of a couple of times where it has actually needed it.
Cleaning it is really easy- though be aware that you are working with LP gas, so proper safety measures should be taken, but you just remove it, soak in alcohol, air dry and reinstall- don’t try sticking anything in it. You can blow a water heater orifice out with compressed air, as well.
–Chris
Hi,
Do you have any idea why my hot water heater seems to be producing water that is a lot hotter than it’s been in the past?
Pam
Hi Pam,
Have you checked the most likely cause, someone turned the thermostat up too high? It would be a simple error to make! It is usually a big red dial on the front of the valve assembly. Normally has a big vertical mark for ideal, and then inciates hotter to the right and cooler to the left. I usually leave mine in the middle.
Good luck!
Don
Hello, my LP water heater pilot won’t stay lit, initially when I light the pilot it will stay on till it heats up the tank then it goes out, then I can’t relight it again. I replaced the pilot assembly and the same thing happens. This water heater is less than a year old. Atwood 6 gallon tank. What else could be wrong? Also, where is the gas valve located? Is that inside the tank?
Thanks,
Yvette
Hi Yvette,
If it’s under a year old, I would just let a service center take care of it under warranty. I have run in to gas valves- shown in the top illustration- with internal temperature related shorts, which would shut off when hot, but work when cold.
I have suburban water heater. It has DSI. I was wondering if it has orifice that I can remove and soak with alcohol? Is it possible to insert a special “round shape” brush into the tube to remove debris and spider web?
Hi Rickie,
Suburban has used a number of different orifice arrangements, and while they are all cleanable, they all have different methods of removal.
That said- the main orifica is not normally a problem, and you can clean out the burner tube with the cleaning brush.
– Chris
I have a standard 10 year old Suburban 6 Gal water heater. Is there a gas instant hot water heater that I can replace mine with?
Hi John,
The only LP fired gas water heater that is certified for RV use that I know if is the Precision Temp RV500- a very good unique product.
The main issue is that it fits in the cutout for a 10 gallon model, larger than the 6 gallon you have by a couple of inches height and width.
I have a couple of customer who have this model, and they all rave about how well it works.
Does anyone know where I can purchase a used Suburban Water Heater?
Thanks
Hi John,
We have an Atwood water heater and it worked fine for the past 8 years (I think it was manufactured in 99). At the end of last summer the pilot light would light fine, the burner would ignite and then after approx. 10 minutes we would hear a click and a poof and both the burner and the pilot would blow out…any suggestions???
Hi,
I have the Atwood hotwater heater that you mention in your post. It is the G6 A-7. I just bought the trailer used and am not sure how to light the pilot light for the hotwater heater. Can you point me in the right direction? I’ve looked at the instructions, but unfortunately nothing is detailed enough to show where to insert flame : – )
Thanks for any help you can give!
Hi Daren,
If you look at the first picture in the article (after my picture ) (click on it for a larger version), where I have the pilot assembly labeled is where you light it- turn the knob to pilot and hold it, hold a lighter (a long necked butane grill lighter is almost mandatory, though I’ve used kitchen matches in a far past).
Hold the knob for at least 15 seconds after the pilot flame lights (I usually hold it for 30 seconds), then it should stay on- turn the knob to “ON”, adjust the temperature to where you want it via the lever on the top of the valve, and you should be set.
Do be aware that if it has not been run in a long time, it will take a looooong time to get the air out of the LP lines.
–Chris
We have a Suburban Mod# SW6ED and when I releaved the TH the red reset light on the controller came on and would not go off. Check everything, propane (ok), ignitor (sparking) but no gas to fire up. Could not smell any propane and main burner would not light.
We do have stove burners working so we know the propane is moving, and we have read all the books but no help—Can YOU?
Hi Curt,
I would start by testing continuity of the 2 gas valve coils (actually, I would start by checking the connections at the gas valve). It sounds like one of the 2 coils may have burned out or be bad.
Next I would check the orifice- which can be tricky on a Suburban, as they have changed the design a few times, and one version has a stamped aluminum orifice which can easily fall out- not a good thing!
I have a water heater that has a spark that ignites when it needs to heat water Recently the gas won’t ignite and then all of a sudden it lights the gas and a flame comes out the side of the water heater vent. Is this an ignition problem or a gas problem.
Hi Keith,
It sounds like the burner tube might have an obstruction- it doesn’t take much, even a single thread of a spider web will keep the propane from flowing fast enough to draw in air.
I would run a brush through the tube.
I’ve cleaned everything and replaced the pilot and thermocouple assembly (6 gal American Appliance water heater). Now, about 5-10 seconds after lighting the pilot, I get flames in the air shutter and have to blow them out by mouth. It did not do this before I took everything apart for cleaning. I’m afraid to turn the main burner on as the air shutter keeps bursting into flames every 10 seconds or so.
Hello John
I have an eden greenhouse heater and the gas valve is the problem
I have stripped the valve down and the only working part is a little electronic device in tne valve this is where the other end of the thermocouple connection srews into can you tell me the name of this part and can they be purchased thankyou
Hello John,
I noticed a mud dobber nest on the opening of the burner tube on my Atwood water heater, when I touched it with my finger it fell down into the tube. The nest covered about 1/4 of the burner tube opening and is not visible in the tube. I stuck a small vacuum hose down it to try to remove it but I couldn’t get it to come out. Could I have damaged anything by sticking the vacuum in the burner tube? How can I get the mud dobber nest out?
I replace the thermacup and still my pilot wil not stay on, I talk to a tech from the company. they told me to look at the bottom of the tank to check if a glass broken or a piece of metal is sticken upward betwenn the two metal probes. they say my water tank is combuster. can you help me turn on my water heater
Hi, I have a Suburban SW10DEM hot water heater. Its making a noise like a pump or bearing going bad. I have turned the power off also tried bleeding the lines for air, also let it get cold and it still makes the womp womping sound. Any Ideas??. Its under warranty buy i’m along way from a service center. I’ve looked at the parts page and I see no pump or anything that could make this sound. Thank you
I seem to having the same problem as Lori’s blog on May 1st , 2008.
I get my Atwood 6 gal water heater going then hear a click and both pilot and main flame go out. Mine seems to happen within about 1-2 minutes. The heater is about 5 years old.
Please help!
Please Help. I have a Suburban sw6 (DSI). Is there an adjustment for the hot water temprature and if there is is how can I go about adjusting it. Thank You!!!!!! Bill
Hi Bill,
That model is not adjustable, but… there are replacement thermostats available at different temperatures- IIRC, the stock is 140°, and both 120° and 130° are available. I believe you need the serial number to get the correct one.
–Chris
Hi We recently bought an ‘89 coachmen catalina—great shape! last night I turned on the water heater switch to clean and it would not shut off —-got REALLY hot.
HELP?
Hi Sandra,
Because you said you turned on the switch, it sounds like you have an electronically controlled (aka DSI) model. These are typically factory set at 140° , which can seem very hot.
That said, if the water is getting hotter than that, most likely the thermostat is bad. Thermostats for DSI models are fairly inexpensive- under $20, and easily replaced.
–Chris
chis i have a 2007 brookside travel trailer the hot water tank will work fine on gas but on electric it wont get hot just warm do you know what i should check i would love to find out whats wrong thanks
I have an Atwood valve like the one in your article. The pilot will not stay lit. I have held the spring loaded dial on pilot for several minutes, but as soon as I let go, the flame diminishes and then goes out. Any suggestions on troubleshooting this? Also, is there a way to check the thermocouple?
Thanks,
Richard Lucas
Sebastian, FL
Hi Richard,
You might look at my post LP Appliance Flame Safety Devices, which gives a method of testing thermocouples.
I will say that this particular gas valve has been a bit failure prone, to the point that Atwood no longer sells it, they have gone to another vendor.
–Chris
I have an Atwood hot water heater in a pop-up camper. It worked fine until recently. The pilot lights easily but when I try to switch it to “on” it will not ignite and the pilot goes out. Any ideas?
I appreciated the article.
I have a 1971 Terry Trailer. From looking at the pictures I assume that my water heater is an Atwood. The flame and pilot light, but it gives just a small steady flame. In other water heaters I am use to, a large roaring flame would burn until it was up to temperature and then turn off. I think that there is something wrong with it, and have cleaned out everything that I can see might have cob webs or dirt in it. Is the steady flame normal, or should I have a roaring flame that shuts off as it gets up to temp?
I was thinking of trying to replace the gas valve, but if I do not need to then I really don’t want to go to the expense.
I have a Suburban SW10DE water Heater. I have some technical knowledge and found that one of the two gas valve coils are bad. I’d rather replace the coils instead of the entire gas valve assembly ($90), but have been unable to find the coils or any of the specs/mfg online. I think it may may a White-Rodgers but got nowhere there. Any info that might help me find the replacements would be greatly appreciated.
I have a 92 Kountry Aire 5th Wheel with a Suburban Hot water heater, The pilot will light and stay lit, up until the thermostat kicks the gas on then the pilot will instantly go out. ( you can lite the burner manualy and when the water heats up the pilot will stay lit up until the water heater tries to turn back on then same old thing, pilot goes out and you have to lite manualy) I already replaced the Thermo couplour the pilot the orifice, and replaced the gas valve twice, to no avail same thing happens would appreciate any ideas, Thanks..