Atwood On Demand

[Phil57]

I have a 2011 Berkshire Motorhome with a Atwood on demand water heater. I had it put in last year and for the most part been happy with it.
This morning I couldn't get any hot water. The light in side indicating combustion did not light. I tried all the normal fixes. Reset clogged black air intake loose wires blown fuse. Nothing. It acted like the black intake was clogged but I removed it and it was clear. I jumped the pressure switch and the heater fired. So bad pressure switch? On a hunch I took the tube off and stuck a piece of wire into the opening in the switch and found a grub like worm in there. Now I have never seen a mud dauber so it could be one. I tried to remove the nipple to clean it out better but I ended up breaking it. With the junk cleaned out it works great. I ordered a new pressure switch so it's a easy fix. And I have hot water until it comes in

[boxers-rule]

Phil,
I have had the same "clogged air pressure switch tube" multiple times now. I generally clean it out lightly with a toothpick and then blow thru it the best I can. It then seems to work for a while.
I have 2 questions. Do you think that just by replacing the switch it will work? And has anyone out there considered some form of filter on the intake tube to stop whatever from getting in there?
I'm not sure if the dirt buildup is from insects or dirt from driving, settling in the tube. As an experiment, after I cleaned it the last time, I took my handkerchief out, opened it to just one layer than placed it over the tube as a filter and the unit still fired up. Unfortunately I think that a filter could get clogged also if the dirt buildup was from simple driving down the highway.
Furthermore, at our last trip when I had discovered that the filter idea could work at least temporarily, while we were parked at the campground on a beautiful day, we were able to get it working in the morning (before we had the tube cleaned out) and by afternoon, it was clogged to the point of not firing up, no driving involved. So that may nix the getting clogged from dirt while driving.
Anybody else have any ideas?
One last comment, the temperature swing hot to just right to hot to cold, etc is driving me crazy.

Rick

[Bama Rambler]

Looks like that's the side that's vented to atmosphere. If so, then a screen or filter will work to keep it clear.

Here are some Suction Line Strainers that would work. US Plastic Suction Line Strainers.



They'd keep out bugs and you'd be surprised how much dirt they'll block

[Phil57]

Originally Posted by boxers-rule

Phil,
I have had the same "clogged air pressure switch tube" multiple times now. I generally clean it out lightly with a toothpick and then blow thru it the best I can. It then seems to work for a while.
I have 2 questions. Do you think that just by replacing the switch it will work? And has anyone out there considered some form of filter on the intake tube to stop whatever from getting in there?
I'm not sure if the dirt buildup is from insects or dirt from driving, settling in the tube. As an experiment, after I cleaned it the last time, I took my handkerchief out, opened it to just one layer than placed it over the tube as a filter and the unit still fired up. Unfortunately I think that a filter could get clogged also if the dirt buildup was from simple driving down the highway.
Furthermore, at our last trip when I had discovered that the filter idea could work at least temporarily, while we were parked at the campground on a beautiful day, we were able to get it working in the morning (before we had the tube cleaned out) and by afternoon, it was clogged to the point of not firing up, no driving involved. So that may nix the getting clogged from dirt while driving.
Anybody else have any ideas?
One last comment, the temperature swing hot to just right to hot to cold, etc is driving me crazy.

Rick

First off I like those screens posted above. That would work better that a filter on the tube itself. I got advice from another member to turn the tube inside the compartment and to tape or plug the hole. I happened to be talking to Atwood CS and they said the design of the tube is faulty and prone to many clogged issues. They recommend the same thing. I did that but failed to plug the hole. One day later I had the same issue. Those Mud Daubers are very persistent. I cleaned it out again and this time plugged the hole and no more problems.
As for replacing the pressure switch I replaced mine because I broke the end where the tube connected. I was sure a Dauber had gotten in side that tube. It was not the case.
As for the temperature swings its import and to remember how the heater works. It's all about flow. On a conventional water heater the temperature is constant and is easily adjusted with cold water. In a in demand the flow controls the temperature as well as adding cold water. So when you have it in full hot and the water becomes to hot adding cold decreases the flow making the water coming from the hot side. That makes the water hotter as it has more time in the heat chamber to super heat. So you add cold and the water gets hotter. Then it gets to cold. Small corrections are needed to get a good shower.

[Phil57]

Originally Posted by Bama Rambler

Looks like that's the side that's vented to atmosphere. If so, then a screen or filter will work to keep it clear.



Here are some Suction Line Strainers that would work. US Plastic Suction Line Strainers.







They'd keep out bugs and you'd be surprised how much dirt they'll block

Great idea. Will they stay on when driving?

[Bama Rambler]

They'll stay on, just measure the OD of the tube and get one that fits. You can glue them on if needed.

[Phil57]

Thanks Bama.