Replacement of WH Gas Valve

Last year I replaced the control board and that solved the problem of no spark to ignite the flame. It did not address the gurgling noise made by the flame. It was not caused by the air/fuel mixture. I ordered a new gas valve from Amazon, installed it and the flame is quiet again. [I know describing a flame as quiet or noisy is not the correct, but it's the best I can do right now]

Installation is easy and I was comfortable doing it. 

Turn off the gas
Unclip the DC supply
Unscrew the gas feed line
Unscrew the single screw that holds the valve to the bracket.
Remove the gas valve.
Remove the gas jet with vice grips and put on the new valve.
Put the new valve in place, attach it to the bracket, put the supply line back on and plug the DC supply.
Turn on the gas and wait much longer than you imagine for the gas to get to the WH.
Fire it up.
Turn it off and check for leaks.

Hot Water Heater Intro

First, thanks to all who helped put this together - John, Erik, Judy and Andy.  They picked up a number of errors and omissions that helped me make it better.  

This is targeted at water heaters from Atwood, used in Lazy Daze motor homes.  It is NOT applicable to other makes of heaters.  It is not intended to be a detailed or comprehensive guide to troubleshooting your heater.  Rather, the intent is to allow you to become familiar enough with the electronics in the system to understand what is going on, and possibly to identify a failed component if professional help is not available.  Other articles address flushing the heater, and I do not plan to address issues with propane delivery here.

Now the disclaimers - Combining propane and electricity is dangerous.  Do not mess with the system if you do not feel able to do so safely.  Read your Atwood manual for more detail.  If you do not have one, you can download one from http://atwoodmobile.com/manuals/waterheaters/MPD%2093756%20SP%2011.19.07.pdf.  Their manual has step by step instructions for troubleshooting, and it is recommended that that be your primary resource.

Stay within your skill set.  If you are not comfortable with any of these steps, let a pro do the work.

Do not work on the water heater when the water is hot.

You may want to take pics of everything before you start, but if you only deal with one component at a time, getting things back together is pretty simple.

These water heaters run on 12 volts for the controls and propane for the heat.  There are some 120v heaters out there, but this does not address them.  They have a confusing array of wires running here and there.  When the heater isn’t working right and you are well away from help, it can be a challenge to figure it out.  This article is intended to give you a basic understanding of the parts, what they do, and perhaps how to check them if you are having problems.

Looking at the heater, in the top right corner is the circuit board.  It is the brains of the operation.  It senses what is happening elsewhere in the system and does things like allow propane to flow or not, send a spark to light the propane, monitor the water temperature, and monitor the flame.

To the left of the Board is the brass pressure relief valve.  It has two functions.  If there is too much pressure in the heater, such as from water that is overheated and boiling, it releases pressure rather than allowing the pressure to build and cause a steam explosion.  It is also used to restore or maintain a pocket of air at the top of the heater chamber which cushions the chamber and your plumbing from overpressure as water heats and expands.

Left of the pressure relief valve is the exhaust vent.

Below the pressure relief valve are two thermostats and a device (thermal cutoff) in a clear plastic tube.  The left thermostat, covered by black foam tape, is labeled ECO (Emergency Cutoff).  It shuts down the system if heater temperatures are too high.  It is normally in the closed position, conducting electricity through it, but if it senses temperatures that are too high it will open, cutting off flow of propane.

The right thermostat is the one the system uses to control the water temperature.  When the water is cold, this thermostat is closed, conducting 12 volts through it, and current can flow to the system.  When the water reaches the designated temperature the thermostat opens, cutting off the electricity, and the system cuts off the flow of propane.

Floating about in front of the thermostats is a little electrical part encased in a clear plastic tube.  This is a thermal cutoff.  If there is too much heat in the area behind the thermostats, perhaps from a blocked flue or exhaust vent, a propane leak or some such, this part melts, cutting off power to the system.  

Andy Baird’s “Eureka” talks about the thermal cutoff.  He said, ”Like a fuse, the thermal cut-off is a one-shot device... so if it blows, it must be replaced. This is where it gets interesting. A Google product search on 'atwood thermal cut-off' turned up prices ranging from $16.00 to nearly $23.00. I knew that a simple part like this couldn’t possibly cost that much—somebody, probably Atwood, was tacking on huge markups. But I was able to locate the part in the Newark Electronics catalog for just $2.16—a far cry from the RV dealers’ pricing! Here’s a link to the item.

http://www.newark.com/nte-electronics/nte8096/fuse-thermal-98-c-15a-277v/dp/55R1324?ost=nte8096&selectedCategoryId=&categoryNameResp=All%2BCategories&searchView=table&iscrfnonsku=false

For the record, it's an NTE Electronics #NTE8096 thermal fuse, designed to carry 15A and cut off at 98 degrees Celsius. It's not something you can find in a local Radio Shack store, so I carry a few spares with me just in case. You might want to do likewise.

To be fair, Atwood’s $20.00 replacement part includes two thermal fuses (worth four bucks), some plastic sleeving, and a couple of 3/16" crimp-on lugs (worth a buck, maybe)—but I'm sure most of us can scrounge those items for a lot less than Atwood is charging!”

Below the thermostat and ECO is the propane solenoid valve.  To the right is the mix tube or burner, which mixes air with the propane and turns and directs the air and propane mixture into the burn chamber.  In front of the mix tube outlet, at the entrance to the burn chamber, is a pair of contacts from a white ceramic ignitor, which acts like a spark plug.

Finally, above and left of the solenoid valve is a plug which allows draining of the heater for maintenance such as flushing or storage.

OK, here we go.  When you switch the heater on and the water in the heater is cold, 12 volts should go first to the thermal cutoff, then to the thermostat, then to the circuit board.  What you see on the panel depends on how old your panel is.  On newer panels, the switch operates a green light to show the switch is on, and the board operates a red light, indicating that the startup sequence has begun.  Proper startup is signaled by a red and a green light by the switch over the stove.  On older panels, there is a single red light, controlled by the board, that comes on with the heater startup sequence. 

When the board receives a 12 volt signal, it accepts that as meaning that the thermal cutoff and the thermostat are closed.  Then the board thinks it is safe to begin lighting the burner to heat water.  It signals with a red light by the switch, and begins the startup procedure, sending voltage through the ECO to the solenoid.  If the ECO is closed, that voltage reaches the solenoid, and the solenoid allows the flow of propane.

The board now sends a high voltage pulse to the ignitor.  Between pulses it measures the resistance across the ignitor’s 1/8” gap.  That resistance tells the board whether there is a flame or not.  It should try three times to light the burner.  If no flame is sensed, it will shut down the propane and cease further attempts.  If a flame is sensed, the lights by the switch go to green and it continues the burn until the thermostat opens, at which time it cuts off the flame.

So - what can go wrong?  Let’s assume here that you do not have dead batteries, and that you have ample propane.  What next?

First, there are a lot of spade connectors in the system.  They are subject to corrosion.  If they become corroded, the board will not get good information and the heater will not work right.  So, start by making sure all the connections are clean and free of corrosion.  Connectors can be cleaned with contact cleaner, with a fine abrasive such as a coarse eraser or fine sandpaper, or by other similar means.  When cleaning the contacts on the board, be gentle.  That material is thin.  You do NOT want to abrade it away.

Next, if you have a multimeter, you can check the thermal cutoff, the thermostat and the ECO for an open circuit or even better, for voltage.  All should read closed or very low resistance.  If any read open, you found the problem.  

If anything - corroded contacts on the board or in the heater wiring, a bad switch, a bad wire coming in (rare, but possible), a bad thermal cutoff, or an open thermostat - interrupts the current, the board will not get 12 volts, and you may see a green light by the switch on a newer panel, but not a red light.  On an older panel you will see no light.  So, if you see no red light when you turn the switch on, and you have a voltmeter, start off by measuring the voltage anywhere in that chain from entry wire to thermal cutoff to thermostat to board connector.  If you do not have 12 volts all the way along, the component “upstream” of the check point at which you do not get 12 volts is the failed component.  Replace the part.  

If you do not have a multimeter, and you have a helper, you can test the thermal cutoff and the thermostat and the ECO by bypassing each of these items, one at a time, by unplugging the spade connectors from the device and connecting the two wire ends together.  WARNING - DO NOT USE BYPASSING TO OPERATE THE HEATER, just to troubleshoot it.  The recommended way is to have a helper inside, with the switch off.  Make the bypass connection and have the helper turn the switch on.  If the heater lights, you found the problem.  Turn the switch off immediately (you disconnected a safety device) and reconnect the failed device until you can get a replacement.  Do the thermal cutoff first, then the thermostat, then the ECO.

The Atwood manual gives places where voltage can be checked with a multimeter.  You could have a working ECO, but corroded contacts, leading to low voltage at the solenoid.  If you have a multimeter, do those voltage tests.

OK, you checked and the thermal cutoff, thermostat and ECO and all are showing closed or good, but you have no flame.  The voltage at the solenoid is good.  Is the solenoid operating?  You may be able to hear gas flow if it is.  My hearing is not good enough for that, but yours might be.  Make sure the mix tube is clear of debris, spider webs, etc., then try again.  If the tube is removed to clean, it should be put back in same location and make sure the flame is adjusted to provide the most efficient air gas mixture.  The color of the flame is the indication of this by seeing a good blue flame with a tinge of yellow on the flame tip. Too much air will be noticeable by a louder burn and yellow flame. This adjustment is done by loosening the screw at the beginning of the tube and making the air gap there larger or smaller, then tightening the screw.  This setting should not be done at higher elevations. 

At this point, some guesswork is involved.  If you see no spark at the ignitor electrode tip, then either the ignitor or the board is bad.  If you see a spark but no flame, you may not be getting adequate propane flow, indicating a problem with the solenoid, you may not be getting air mixed with propane, or the spark may be weak or in the wrong place.  If you see a flame that burns briefly before going out, either the ignitor or the board is probably bad, but a blocked mix tube or propane orifice could be to blame.  

Let’s look at the ignitor.  You should hear a tic - tic - tic sound as the ignitor shoots a spark across that 1/8” gap, and unless you are in bright sunlight you should be able to see the blue spark.  You might even see a jet of flame come on, burn briefly, then go out.  Remember, the ignitor does more than just throw a spark.  It also tells the board when a flame is present.  A dirty ignitor, corroded electrodes or a crack in the ceramic can result in improper resistance, shutting down the gas flow.  The ignitor can be removed fairly easily.  The Atwood manual says, “The gap between the sparking probe and the ground probe should be 1/8”. The probes should be clean and free of cracks, flaking and corrosion. Position the probes so that they are in the path of the gas flow. Cracks in the ceramic insulator can also be the source of an intermittent problem. To check for cracks insert a fiber washer or any other type of insulation material in the 1/8” gap between the rods. Remove the gas valve from the circuit and turn the unit on. If you see a spark jumping from the ceramic to the ground rod or bracket, replace the spark probe.”  

If you service the ignitor electrodes, after cleaning the igniter rods the gap adjustment should be made with two pairs of pliers, one to hold the straight rod right above the ceramic to not put undue stress on it while bending the curved rod with the other pair.  If you have gotten the ceramic wet, it is somewhat porous and may take a while to dry completely.  Rain won’t do it, but direct water spray, such as your hand slipping when flushing the heater can do it.  Guess how I know that…  Until it is dry, it may send a bad resistance reading to the board, preventing the heater from working.  A day of dry conditions should deal with a moisture problem. 

OK, the thermal cutoff is good, the thermostat and ECO are good, and you see nothing wrong with the ignitor, but you still have no hot water.  The remaining problems are gas flow and a bad board.  A board is not cheap, but can be replaced fairly easily.  It is NOT RECOMMENDED that you mess with the solenoid or the propane orifice.  There is simply too much risk if you mess something up. If you are confident that propane is flowing, but you have no flame, your problem is pretty much narrowed down to the ignitor or the board.  The ignitor is cheap.  Replace it.  Still no good?  Now, finally, it is time to try replacing the board. 

Hopefully, this will help you understand the heater’s steps and may give you a clue what to look for if you are having problems.  Again, stay within your skill set on this.  With some understanding and a sense of how the parts work together, you may be able to figure it out.  If not, get thee to a qualified service person.

Ken Fears - September 2016

As Editor I can not resist adding a few very minor points to this fine article.

Note the nylon drain plug in the picture, a suggested improvement. One way to easily remove the drain plug is with a socket wrench with an extender and a swivel. That allows you to get around the gas plumbing.

Also note the position of their air/fuel “mixer tube”. It's all the way to the left. That position may yield the bluest flame. You need to know this if you disassemble the tube for cleaning. That needs to be done every few months of use. A few minutes with a wire brush and WD40 will clean it up.

I have my spare thermal fuses in a ziplock bag taped to the inside of the heater cover, so I can find them if I ever need one.

The adjustable thermostat allows you to lower the temperature to the level you find most useful. Some set it so that no cold water needs to be mixed. We keep ours at 120. I think the factory setting is about 140. How do you know what the temp is? You add an aquarium thermometer to the tank.  I guess we need to add a How To for that Andy B improvement. Nothing to it, just place the temp prob under the tank insulation and run the wire to the display.

Hot Water Heater - Draining/Flushing/Sanitizing

Draining
It is recommended that you drain and flush the hot water heater one or two times a year. Calcium sediments build up, especially is the southwestern states. It should also be drained if you will not be using the RV for an extended period of time or if the motorhome will be stored in during a time of sub-freezing temperatures. Should you let water remain in the tank for a lengthy period, it is likely to develop a VERY foul odor, and a thorough flushing and sanitizing of the tank will be required to eliminate the smell.

To drain the water heater, turn off the water pump or city water. Then remove the plastic drain plug located in the lower left portion of the water heater; it is accessible through the exterior service door. A 5/8" socket on an extension makes the job easy. After removing the drain plug, open the pressure-relief valve to allow air to enter the heater for faster draining.

Many people replace the plastic drain plug with a petcock that can opened for draining, rather than having to remove the plug. With a petcock, you can also put an adaptor on it so you can attach a short piece of hose to prevent the water from running down the side of the motorhome. Of course, to properly flush the heater, you will have to remove the petcock.

Flushing
The easiest way to flush out the water heater is with a special flushing tool available at RV parts stores. It attaches to the end of a water hose and you insert it through the drain opening and spray the inside of the heater. Repeat a couple of times for best cleaning.

Flushing can also be accomplished without the special flushing tool:

a) wait for a warm day, wear sandals
b) heat the water maybe halfway to increase solubility of the stuff
c) pump off, open drain, open air vent, let it flow
d) use a garden hose with a nozzle that fits partway into the drain.
e) with the nozzle tight into the tank, inject some water. If I'm hand-holding the nozzle I'll be able to hold about half as much pressure as the pump would give. That's what I want.
f) watch as the soft crystals spray on your feet.
e) rinse and repeat

Sanitizing
Turn off the water pump and drain the water heater. Add vinegar to an empty water tank, usually 3 or 4 gallon jugs, add some water to that and run the pump until the water heater fills up. Turn it on and let it heat up and then off and let it cool down. If you're in a hurry, not somewhere you can use water from another source, don't heat it up but just let it sit in the tank for an hour or two. Also run the water through the faucets to get some vinegar on them as well. Drain the water heater and use the flush wand until it the water runs clear. Drain and refill the tank and run it through the faucets to clean them as well. Drain the water tank again, refill and you're done. It is recommended that you do this twice a year. It's amazing how much gunk comes out.

Removing that VERY foul odor
Bob Livingston's "The RV Repair and Maintenance Manual" describes this procedure to 'remove foul odors from hot water tanks":

- Shut off the water supply.
- Drain the tank via the plug (anode rod if so equipped.)
- Remove the pressure relief valve (the valve in the top portion of the unit with the lever that releases pressure.
- Replace the drain plug or anode rod.
- Pour in three to four gallons of white vinegar through the relief valve opening (use a funnel).
- Replace the pressure relief valve.
- Open the closest hot water faucet and turn on the pump so the tank fills.
- Turn on the water heater and cycle until the flame shuts down.
- Close the water supply.
CAUTION: THE WATER IS VERY HOT AT THIS POINT.

- Remove the drain plug or anode rod and drain the tank.
- Replace the drain plug and anode rod and refill the tank.
- Repeat if necessary.
- Perform this procedure at least twice a year to maintain a fresh-
smelling tank.
Contributors: John, Jonna, WxToad

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Hot Water Heater - Trouble-Shooting

Troubleshooting a Atwood Hot Water Heater

Restore air pocket in the tank - see Leaking Pressure Relief Valve.

Won't start or stay on

Check the wire connections - remove, clean and replace

Check house batteries for low voltage

Ensure you have propane

Check for air in tank

Check the thermal cut-off

See whether its clear plastic sleeve is burned or melted. The thermal cut-off is a small diode-like electronic part encased in a clear plastic sleeve, hanging out in midair a few inches above the burner tube's air slots. It is a safety device to prevent a fire if the main burner malfunctions due to obstructions caused by spiders or mud wasps. These obstructions can cause the main burner flame to burn outside the main burner tube. Another scenario where flames can emerge from the air slots is when propane pressure is low. That could happen if you run out of propane, if you take on a load of propane laced with butane in a warm part of the country and then drive to a cold area where the butane won't vaporize, causing a pressure drop, or if your regulator is faulty. If the flame or the heat from the flame contacts the thermal cut-off, the circuit will open.

If it appears damaged, you can verify that it is the problem by bypassing it with clip leads to see if the HWH will then operate.

Like a fuse, the thermal cut-off is a one-shot device... so if it blows, it must be replaced. The Atwood part number is 93866. Atwood sells a replacement kit which includes two thermal fuses, some plastic sleeving, and a couple of 3/16" crimp-on lugs. A cheaper equivalent is the NTE Electronics #NTE8096 thermal fuse, designed to carry 15A and cut off at 98 degrees Celsius.

On my burnt out thermal cut-off, the male and female 3/16" (.187) connectors were both crimped and soldered to the leads. If you decide to make your own replacements be aware that you need to gently clamp a Vice-Grip or pliers with a rubber band wrapped around the handle to provide a good thermal contact between the connector you are soldering and the cut-off device. This heatsink is important; if you don't do this the heat from the soldering operation will probably melt the pellet inside the device and "blow" it. You should both crimp and solder like Atwood does on their replacement kits. This device is in a hostile environment and if the crimp is not perfect, corrosion can build up inside the connector causing resistance and problems. When you are finished check it for continuity.

Be sure you have resolved the problem that caused the cut-off to do its job, i.e., remove any obstructions and ensure full propane pressure.

If you have recently drained the hot water tank, it may now be full of air. Open a hot water faucet to let the air out and the water in.

Soot on outside of panel cover
Soot coming from the water heater indicates a too-rich propane/air mixture, resulting in unburned hydrocarbons. This can happen at high altitudes as a result of physical clogging of the air inlet tube (usually by insects or webs); or because the air/propane adjustment has slipped due to the vibration and jolts of travel.

You need to adjust the mixture by loosening the screw on the slotted air-intake tube, then moving the tube back and forth until the flame is mostly blue with just a hint of orange at the tip. This photo shows an older, pilot-light-type Atwood heater, but the tube is the same.

Broken Tabs on Circuit Board
You may find that both the upper and lower tabs are broken, and the circuit board may also have a crack in the plastic housing on the back of the unit. The design and material of the tabs that attach the circuit board to the housing wall cause the breakage; the tabs are flimsy plastic, and when the screws are put through the holes in these "ears" and tightened snugly enough to keep the board from wiggling, the backward pressure can snap off the tabs.

Use a quick-drying, clear epoxy to attach the tabs to washers, positioning the tab screw holes over the holes in the washers. Then attach the tabs (with their washer backings) to the circuit board, epoxy the crack in the back of the board housing, let the thing dry overnight, and re-install it. The washers serve as support to keep the tabs vertical so there's no stress on them when they're screwed into the metal water heater compartment.

Low Flow at Hot Water Faucets

- Could be a BIG air bubble in the water heater. With the pump on, open the tank relief valve until water comes out, then close.

- There is a cold water entry line check valve that may be stuck mostly closed. This check valve is to prevent hot water flowing back into the cold water lines, and evidently, mineral deposits can build up it to prevent it from opening all the way. This would give you poor flow at any faucet.
Apparently, this valve can be removed and cleaned, or replaced.

Contributors: Andy Baird, WxToad, Erik H, Joan Taylor, Ron, Chuck
Revised 18, Nov 2017

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Leaking Pressure Relief Valve

First off, you need an air head in the HWT, and the easiest way to establish an air head in the tank is to simply turn off the pump, turn off the city water service, open the pressure/temperature relief valve and let it run until there is no water coming out. This lowers the water level to the valve level, thus leaving an air head in the tank. Turn on the city water or pump and let it fill the tank. Your head is re-established and there will be a very minimum of air in the water lines.

Now as to the continued drip. If you are operating your water heater as many LD'ers do, short cycling to get to temperature, then turning off until next time, you will probably always have the drip. This is due to the temperature differential in the tank vs. the valve and it's more condensation in the valve than leakage. If you read your water heater manual you will probably find this "NOTE" therein. You wish to install an adjustable thermostat.

If you are running the water heater in a continuous mode, i.e. turn it on and leave it on until you travel again, and you have a leak then you have a bad valve. It is possible to damage these valves during installation if you don't have the wrench that is designed for them. If you're using a pipe wrench or other wrench it helps to remove the burner shroud to the left of the valve and work gently, not torquing the valve too hard. They look tough, but there is a lot of hollow area in the valve.

It is especially important that when you have the valve open and are through doing whatever, let the lever snap closed. Don't be gentle with it or the seal will frequently not make up due to some "stuff" left on the seal. Just let it snap on it's own force. Once a year or so soak it in white vinegar.

Contributor: Mike Sylvester