Possible Solution to Dometic Furnace issues

[mvassallo]

There are a substantial number of Forum members who have posted about issues with their Dometic Furnaces acting erratically. Friends of mine purchased a new Escape trailer which was delivered this past summer. They immediately had troubles with their furnace trying to fire but not running consistently.

The following piece of advice has worked for 2 of 3 members I have contacted through private messages.

I made a couple of inquiries on my friend’s behalf and as part of this search I spoke with the service manager at Bish’s RV in Cheyenne, Wyoming. As part of that conversation he volunteered that they found the following to work at times when problem solving Dometic Furnace problems that are difficult to explain.

For Dometic Furnaces only, they find that they need to open an additional vent regardless of the size of the furnace.

With the Escape installed Dometic furnace, there are openings available for use if desired on the sides, top, and back of the furnace (facing camper interior) which is the one Escape uses to provide heated air to the camper. There may be one on the bottom but I do not know.

After confirming that gas pressure (using manometer) and power (using Multimeter) were good at the furnace we did the following based on the “hint” from Bish’s RV.

Since there does not seem to be much room around the furnace to utilize a second vent, we removed the inside heater grate removing the screws holding it on the wall. Then we removed the flexible hose from the furnace by snipping the zip tie holding it on to the furnace. Holy Cow! The furnace consistently worked as it should.

We found the slightest impediment to the air flow caused the furnace to revert back to not working properly. We had a Heating/Air conditioner place fabricate a piece of aluminum tubing (nice price @ $5) to reach from the furnace to the vent.

To attach the pipe to the grate, it helps to file off the 4 little plastic bumps used to hold the flexible tubing onto the front grate. (Take the front grate to whomever you have help you build this piece of aluminum tubing for proper sizing.)

We connected the tubing to the furnace front grate and turned on the furnace. UGH! Once again, the furnace did not function properly. Next step?

We carefully popped out and off the center plastic rotating piece of the grate. The furnace worked perfectly.

Since the furnace was not installed needing to be exactly positioned for an inflexible piece of tubing it may be a bit off center which will not allow the grate to fit perfectly. Of course, the solution to this is to adjust the furnace itself a tad to better align everything.

I believe some of the furnace problems folks have encountered are related to a bit of airflow reduction caused by the flex hose and rotating center grate.

The test for this is simple. Simply take off the grate, disconnect the flexible tubing from the furnace side, re-start the furnace and see what happens. Too easy not to give it a try.

Once again, this fixed 2 of 3 forum member’s furnace problems.

Remember, I just asked the question and the answer worked in 66% in this very small sample.

Stay well.

[Eggscape]

I see no reason why the tube could not be made larger in diameter or even square, providing more volume. Of course it is a well known fact that plastic dryer type hose does not allow air to flow as good as a metal tube.

This is a good catch and thanks for passing the tip on.

I just attached a few pic of the front of the furnace once you remove the grill.

[tractors1]

Interesting as the increased air flow would definitely help with more force on the tempermental sail switch.

[Ronn]

Originally Posted by mvassallo

There are a substantial number of Forum members who have posted about issues with their Dometic Furnaces acting erratically. Friends of mine purchased a new Escape trailer which was delivered this past summer. They immediately had troubles with their furnace trying to fire but not running consistently.

The following piece of advice has worked for 2 of 3 members I have contacted through private messages.

I made a couple of inquiries on my friend’s behalf and as part of this search I spoke with the service manager at Bish’s RV in Cheyenne, Wyoming. As part of that conversation he volunteered that they found the following to work at times when problem solving Dometic Furnace problems that are difficult to explain.

For Dometic Furnaces only, they find that they need to open an additional vent regardless of the size of the furnace.

With the Escape installed Dometic furnace, there are openings available for use if desired on the sides, top, and back of the furnace (facing camper interior) which is the one Escape uses to provide heated air to the camper. There may be one on the bottom but I do not know.

After confirming that gas pressure (using manometer) and power (using Multimeter) were good at the furnace we did the following based on the “hint” from Bish’s RV.

Since there does not seem to be much room around the furnace to utilize a second vent, we removed the inside heater grate removing the screws holding it on the wall. Then we removed the flexible hose from the furnace by snipping the zip tie holding it on to the furnace. Holy Cow! The furnace consistently worked as it should.

We found the slightest impediment to the air flow caused the furnace to revert back to not working properly. We had a Heating/Air conditioner place fabricate a piece of aluminum tubing (nice price @ $5) to reach from the furnace to the vent.

To attach the pipe to the grate, it helps to file off the 4 little plastic bumps used to hold the flexible tubing onto the front grate. (Take the front grate to whomever you have help you build this piece of aluminum tubing for proper sizing.)

We connected the tubing to the furnace front grate and turned on the furnace. UGH! Once again, the furnace did not function properly. Next step?

We carefully popped out and off the center plastic rotating piece of the grate. The furnace worked perfectly.

Since the furnace was not installed needing to be exactly positioned for an inflexible piece of tubing it may be a bit off center which will not allow the grate to fit perfectly. Of course, the solution to this is to adjust the furnace itself a tad to better align everything.

I believe some of the furnace problems folks have encountered are related to a bit of airflow reduction caused by the flex hose and rotating center grate.

The test for this is simple. Simply take off the grate, disconnect the flexible tubing from the furnace side, re-start the furnace and see what happens. Too easy not to give it a try.

Once again, this fixed 2 of 3 forum member’s furnace problems.

Remember, I just asked the question and the answer worked in 66% in this very small sample.

Stay well.

Great info, and I am in agreement with tractors1, this makes sense to me.

Originally Posted by tractors1

Interesting as the increased air flow would definitely help with more force on the tempermental sail switch.

[rubicon327]

Originally Posted by mvassallo

For Dometic Furnaces only, they find that they need to open an additional vent regardless of the size of the furnace.

With the Escape installed Dometic furnace, there are openings available for use if desired on the sides, top, and back of the furnace (facing camper interior) which is the one Escape uses to provide heated air to the camper. There may be one on the bottom but I do not know.

Just a point of clarification - Escape uses the DFSAD12 model which can only be ducted with a single outlet on the front. This is due to the use of the low amp motor on that model which helps it to be quieter and use less battery power. The knockouts you are seeing are only because Dometic uses the same small furnace casing for the DFS12, DFS16 and DFS20 that allow multiple ducting options.

Originally Posted by mvassallo

We carefully popped out and off the center plastic rotating piece of the grate. The furnace worked perfectly.
I believe some of the furnace problems folks have encountered are related to a bit of airflow reduction caused by the flex hose and rotating center grate.

Great info and I concur. If the flex duct and/or front grille is installed in such a way that it restricts airflow that will be troublesome. Also what is the return air path on these furnaces? If it’s just the balance of the front grille unused by the supply duct connection that is likely inadequate especially if they are built as tightly into the cabinetry now as they appear. The total resistance is what the motor needs to overcome to move the specified airflow. It’s possible that also lowering resistance on the return path would help the furnaces as well. On the 21 a strategically placed grille on the side of the drawer stack could work. It might be difficult to measure for the average owner but the furnace is supposed to be moving 60 CFM.

Full manual here for reference:
https://www.dometic.com/assets/55/72/33400_55572.pdf

[Ronn]

Originally Posted by rubicon327

Just a point of clarification - Also what is the return air path on these furnaces? If it’s just the balance of the front grille unused by the supply duct connection that is likely inadequate especially if they are built as tightly into the cabinetry now as they appear. The total resistance is what the motor needs to overcome to move the specified airflow. It’s possible that also lowering resistance on the return path would help the furnaces as well. On the 21 a strategically placed grille on the side of the drawer stack could work. It might be difficult to measure for the average owner but the furnace is supposed to be moving 60 CFM.


https://www.dometic.com/assets/55/72/33400_55572.pdf

It seems to me when the sail switch issue first came up many were placing a filter for inlet (return) air. If so, I wonder how that has worked out?

[PGDriver]

For what it’s worth I replaced my flex ducting from the heat box to the grill with standard metal ducting years ago and have never had a problem. Who knows maybe I never would have had a problem but it’s just something I wanted to do.

Cheers
Doug

[rubicon327]

Originally Posted by Ronn

It seems to me when the sail switch issue first came up many were placing a filter for inlet (return) air. If so, I wonder how that has worked out?

I wonder too. I remember mentioning in one of those threads that it better be a real cheap, low resistance filter fabric. Basically just something that could catch some pet hair. If the design allowed what would be really nice is a separate return grille of adequate size with filter fabric behind it.

[hondasaurus]

Originally Posted by rubicon327

I wonder too. I remember mentioning in one of those threads that it better be a real cheap, low resistance filter fabric. Basically just something that could catch some pet hair. If the design allowed what would be really nice is a separate return grille of adequate size with filter fabric behind it.

I've been running on the cold air intake of our trailer a piece of no see um screen for a bit more than a year. Trailer is june 2019. Last autumn we use the trailer in really low temp during hunting season with that set up since we have a dog (maltese) and burned around 30# of propane on a 5 night trip. We use the trailer during this summer and a bit of furnace. Returning hunting this year and after another 20# or so of propane my heater, decided on the last night, that it needed a break (started the fan but refuse to ignite). At home, I look at the sail switch (clean as a whistle). A look at the air intake screen showed (build up of dust) witch the vacuum took care.

Fired the heater between the two separate operation and it fired with the air intake filter dirty and clean

[Oldtimer]

The RV gremlins at work

[TTMartin]

Originally Posted by tractors1

Interesting as the increased air flow would definitely help with more force on the temperamental sail switch.

Yes, that is all that it is doing increasing air flow across a temperamental sail switch.

Before doing that I would try changing out the sail switch perhaps finding a less temperamental one.

[tractors1]

Originally Posted by TTMartin

Yes, that is all that it is doing increasing air flow across a temperamental sail switch.

Before doing that I would try changing out the sail switch perhaps finding a less temperamental one.

The switch itself is just a microswitch mounted to a piece of sheet metal, but might be tough to find with different specs and same mounting holes. I bought them for around 15 cents 30 years ago, but who knows now. It might be fun to try adding a bigger sail instead - maybe with VHB tape to expose more cross sectional area to the airflow. I played with a suburban furnace on a bench 25 years ago and found that then switch had to be open to start the ignition sequence logic, then had to be closed by sufficient airflow for voltage to be sent to the gas solenoid valve for the gas to flow. Didn't work to just jumper around the switch - it is a safety device after all.

[Amel]

I will add my 2 cents into the conversation. We are new escape owners, just received our brand new 21NE at the beginning of November. On our first trip that we took it on we had no problems with the furnace. We were at a local State Park and everything worked out great. We brought it home and put it in the barn for storage. One day it was getting kinda cold and I thought I would go out there and just turned the furnace on, utilizing battery power only. That is when I started experiencing the issue where the fan would run constantly but you could hear the burner clicking on for five seconds and then turning off for 10 seconds. In my experience it started improving and running for longer and longer the more I left it on. Did not know if things needed to "warm up" or what was going on.


Unfortunately, I really don't have too much of a solution. However, when I ran a power cord out to the barn and plug the escape up the problem went away completely. On a cold start, after have been running all day, it never did that constant on and off again. I'm no electrical person, but I'm guessing it has something to do with running the furnace on battery power. Would love to know if anyone else seeing this issue is experiencing it on battery and when connected to shore power.