LP Appliances- pilot type water heaters
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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.