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Trouble starting water heater
The water heater has been acting up for 2 days now.  When I flip the red switch on the inside control panel, I can hear the water heater igniting.  After about 10 seconds I can hear an audible click and it turns off.  Recycling red switch will produce the same outcome.  If I just leave the switch on, the cycle repeats 4-5 times, then the heater will remain on and functions normally.

Two issues that I should point out.  One is that the heater has always made a rather loud roar when heating the water.  It’s done this since I first picked it up at the rig at the factory 2+ years ago.  I’ve read about adjusting the air mixture and have been planning to do that but I haven’t yet got around to it.  The second is that there was a very hard rain the last two days that cleared up yesterday afternoon.  There is nothing wet that I could see but maybe the rain had an impact.  I really don’t know if either of these issues have any bearing on the problem I’m experiencing now or it’s something completely unrelated.

I would greatly appreciate if anyone has any advice, thoughts or experience with this problem.  Thank you 😊

- John
Fulltimer with a 2021 MId-Bath “Babe”, 1996 Cherokee “Scout” and “Bandit” the wonder dog 🐶
Re: Trouble starting water heater
Reply #1 –
A normal water heater startup consists of the flame igniting (spark and fuel), and then the control board waits for a signal from the flame sensor that the heater is lit.  Absent that signal, the fuel shuts off since you don't want raw propane flowing if it's not turning into a flame. 

From your description, it sounds like the flame sensor portion is malfunctioning. 

I've had this happen in my much older rig, especially on damp and rainy days.  In my case, it moisture was getting into the wire where it plugs into the control board.  This happened on a long trip, and I got in the habit of going outside on wet mornings with a hair dryer and drying out the connection before starting the water heater.  Replacing the flame sensor solved my problem. 

There are other things that can cause similar behavior (like a failed control board or maybe low propane pressure), but hopefully that gives you a place to start. 

Search youtube for videos on how to adjust the flame.   It's also possible to test the flame sensor with a multimeter if that's something you're comfortable with.

Rich
2003 MB
Re: Trouble starting water heater
Reply #2 –
Thanks Rich, I should have thought about being an intermittent flame sensor.  I do have a good Fluke multimeter and will test the sensor later today after I arrive at my new camp.  Being an intermittent problem, the flame sensor may dry out and test ok, but it’s a cheap part to replace either way.

- John


Fulltimer with a 2021 MId-Bath “Babe”, 1996 Cherokee “Scout” and “Bandit” the wonder dog 🐶
Re: Trouble starting water heater
Reply #3 –
Definitely adjust the air mixture, John--it's dead simple. Just loosen this small hex-headed screw and slide the slotted tube back and forth until the flame sounds reasonably quiet, then retighten the screw.

X

As shown here, it's set for sea level (minimum air). For higher altitudes you'd slide it to the left to admit more of that thinner mountain air.  It's something you should adjust whenever making a major change in altitude.
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Trouble starting water heater
Reply #4 –

Hi Rich, and John;  Outdoor electrical connections often benefit with a small amount of dielectric grease. While it does attract dirt, it keeps moisture out.  That keeps the metal in good shape and connections working.  Amazon.com: Permatex 81150 Dielectric Grease.33 oz. : Automotive   I've got a 10 oz. tube at home, but this small amount can travel with you. I've also used it on light bulbs and refrigerator connections. 
    The thermal fuse on the water heater, connected at the temperature sensor (switch), along with associated wiring can also cause this intermittent problem.  RonB

As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Trouble starting water heater
Reply #5 –
For more information on the thermal fuse, see this page.
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Trouble starting water heater
Reply #6 –
Quote from: Andy Baird  - 
Definitely adjust the air mixture, John--it's dead simple. Just loosen this small hex-headed screw and slide the slotted tube back and forth until the flame sounds reasonably quiet, then retighten the screw.

[attach type=image]35061[/attach]

As shown here, it's set for sea level (minimum air). For higher altitudes you'd slide it to the left to admit more of that thinner mountain air.  It's something you should adjust whenever making a major change in altitude.

Andy,
It appears that Dometic decided to change things around and there is no longer a mixture adjustment on their newer water heaters… see photo.  I just googled adjusting the gas mixture on my 2021 model WH-6GA and there’s a lot of comment on the subject.  I’ll have to investigate more.

- John

Fulltimer with a 2021 MId-Bath “Babe”, 1996 Cherokee “Scout” and “Bandit” the wonder dog 🐶
Re: Trouble starting water heater
Reply #7 –
After driving for about 3 hours today I’ve stopped at a new campsite and of course the water heater started right up.  I’ve just spent the last hour searching Google for an answer and haven’t found much in the way of a flame sensor.  There is a single wire electrode that you can see in the center-bottom of the photo.  There’s a black wire coming out of it and a high voltage connector at the other end that connects to the controller module.  I pulled the black wire off the controller module and the electrode measures about 21.5 ohms to ground when cool.  If I turn on the water heater switch I can hear the igniter spark but the gas won’t ignite until I reconnect the black wire to the controller module.  The high voltage connector leads me to believe this is part of the igniter but the resistance value and the fact that I can hear the ignition spark when it’s disconnected leads me to believe it’s the flame sensor. The electrode goes for $23.87 online and if the problem persists then I’ll try replacing it.  For right now it’s working so let’s just see how it goes.

- John
Fulltimer with a 2021 MId-Bath “Babe”, 1996 Cherokee “Scout” and “Bandit” the wonder dog 🐶
Re: Trouble starting water heater
Reply #8 –
Hi John; When the flame is lit, there are a lot of free electrons (plasma) in the area, and the resistance to ground is very low.  So with more sophisticated electronics, the flame controller can tell when the flame is lit. I've heard people say that the igniter probe needs to be moved sometimes to detect the flame better.  Also the end of the igniter seems to collect debris and sometimes needs to be cleaned or sanded off, if there is corrosion.  You might try that first.   RonB 
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Trouble starting water heater
Reply #9 –
Quote from: RonB  - 
Hi John; When the flame is lit, there are a lot of free electrons (plasma) in the area, and the resistance to ground is very low.  So with more sophisticated electronics, the flame controller can tell when the flame is lit. I've heard people say that the igniter probe needs to be moved sometimes to detect the flame better.  Also the end of the igniter seems to collect debris and sometimes needs to be cleaned or sanded off, if there is corrosion.  You might try that first.   RonB

Thanks RonB, I had no idea the system was so sophisticated.  I’ll try cleaning and/or repositioning when it fails again.

- John
Fulltimer with a 2021 MId-Bath “Babe”, 1996 Cherokee “Scout” and “Bandit” the wonder dog 🐶
Re: Trouble starting water heater
Reply #10 –
Looking at your picture, the igniter/ flame sensor is the white porcelain with the black high tension wire mounted to the burner assembly.
you can remove the Philips screw and the whole assembly will come out. Clean the tip with a pocket knife or some sand paper and reinstall and see what happens. I would recommend not messing with the gap unless you actually have to. It is kind of critical. Of course make sure all the electrical connections are tight. Make sure the power is off when you are working with that ignitor, it's like a spark plug and it'll zap you good.

Jon
1994 MB
 
Re: Trouble starting water heater
Reply #11 –

Atwood water heaters use a 1/8" spark gap at the ignitor. If the ignitor is pulled out for cleaning, make sure the gap is correct.
Check the porcelain insulator for cracks and the mount and screw are clean and tight.
Make sure the propane pressure is adjusted to 11-in/h2o with two propane appliances running, set with a manometer.

A manometer is a handy tool, I have both a DIY version made with clear plastic tubing and wood years ago and also an electronic model that is carried in the LD all the time
Amazon.com: PerfectPrime AR1890 Professional Digital Air Pressure Meter &...
DIY manometer
https://duckduckgo.com/?t=h_&q=diy+manometer&ia=web

Larry

As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze