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Old 05-09-2014, 01:48 PM   #1
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Dometic RM2551 (2008 unit) LPG Check Light Problem

I have a Dometic RM2551 with a manufacturing date of 2008, Serial Number 827-00095. It is in a 2006 Safari that had a weld in the ammonia tubing break and I kept the replacement repair unit for a spare and purchased a new Dometic to replace the original.

This unit works perfectly on the electrical grid.

This unit began having the "check light" come on infrequently after a couple years of use. Last year the "check light" came on more frequently and this first trip using the LPG option the check light needed to be turned off and on two to a dozen times before it would keep the burner lit and frequently during, usually cold evenings.

On our return I popped the cover off of the control panel attached to the back of the unit and it is different than the 2006 control panel, so I could not just swap it out to see if the control panel was the source of the problem.

Since we were camped for three weeks I spent free time trying to figure out the source of the problem...

Symptoms:
(1) Outside temperature is hot... unit operates with few if any resetting. The time the propane flame is extinguished is on a cold starting and needs numerous check light restarts to get the unit to operatre.
(2) On the first electronic ignition the propane burns blue and well.
(3) When the unit fires up, there is a "boing" sound that seems to be mid center of the ammonia coils, but there are no sensors that can be seen. The propane blue flame is then out, as the gas solenoid valve closes.
(4) After the On/Off and Check Light resetting some heat is generated above the flame and this heat seems to cause the unit to operate until a future automatic sensor triggers the propane to reignite and cool the system.
(5) The burner and Flue Tube are clean. The two fuses appear to be fine in the Control Panel.

The 2008 Gas Equipment Assembly does not have a Thermocouple, although the hole is provided for one. My 2006 has a Thermocouple in that spot.

If in the trailer you will hear the ignitor light the flame and you will hear the "boing" and the check light comes on, needing to go through the On/Off numerous times to get the system to operate.

There is a temperature sensor that is clipped onto the metal fins beneath the freezer compartment. I suspect that could be the or a source of my problem, but have no way to check.

The manual speaks of a "limp mode" but this does not seem to operate, if that is a clue. That would be better than having to constantly checking to see if the "check light" is on and having to reset numerous times to keep the propane side of the operation operating.

Has anyone encountered this before and have a suggestion?
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Old 05-09-2014, 02:32 PM   #2
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Quote:
There is a temperature sensor that is clipped onto the metal fins beneath the freezer compartment. I suspect that could be the or a source of my problem, but have no way to check.
I don't think that is your problem because if it were defective it would have the same effect when on AC.

Sounds to me the burner is being starved for gas so that even though the burner starts gas to the burner is not being sustained. Possible causes: 1) empty or near empty tank; 2)leak in gas line; 3)partially clogged orifice.

First thing I would do after checking LP tank level(s) is make a manometer (search for manometer thread to see how to make a manometer) to be sure you're getting proper gas p.s.i. (~11 lbs.) then clean or replace orifice and adjust burner if needed.
Not sure about the "boing" you're hearing, but my guess is it has to do with the solenoid cutting off the gas line when there's insufficient flow.

My 2 cents. Hope it helps.
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Old 05-09-2014, 03:28 PM   #3
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I had an issue with our frig last year. Long story made short: the igniter is also the thermo-couple. Make sure the ignitor/thermocouple is in the flame. If the wire connected to the ignitor gets bumped it will move the tip away from the flame. It will then light but go out because it is not sensing a flame.
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Old 05-09-2014, 04:41 PM   #4
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Acstokes, you are right on the temperature sensor.

Both tanks are full of propane.
No smell of leaking gas and the cook top, furnace and hot water tank work fine.
Partially clogged orifice made me pull off the cover to inspect, but although it appeared clean... that was always a good possibility.

Landrum.
The igniter above the blue flame has a glowing orange tip and the spark ignites the propane immediately... Would that cover me that the igniter/thermocouple. There is a J2 male plug that has no wire attached to it on this control panel attached to the outside bottom left, although when installed there was a loose blue wire with a round pin female connection with nothing to attach. It worked when installed, so must be something that is needed for something other than an Airstream (?).

Thank you both!

I am understanding the process, but might have to break down, hook up the Safari and have the professionals work this out for me. This is my last attempt to be able to do an on site repair anywhere or anytime...
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Old 05-09-2014, 05:28 PM   #5
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Dometic RM2551 (2008 unit) Check Light Problem

(I posted this in General Appliances and found this more appropriate Thread. Please refer back to General Appliance Topics with same title for additional comments made today. Thank you.)

Dometic RM2551 (2008 unit) LPG Check Light Problem
I have a Dometic RM2551 with a manufacturing date of 2008, Serial Number 827-00095. It is in a 2006 Safari that had a weld in the ammonia tubing break and I kept the replacement repair unit for a spare and purchased a new Dometic to replace the original.

This unit works perfectly on the electrical grid.

This unit began having the "check light" come on infrequently after a couple years of use. Last year the "check light" came on more frequently and this first trip using the LPG option the check light needed to be turned off and on two to a dozen times before it would keep the burner lit and frequently during, usually cold evenings.

On our return I popped the cover off of the control panel attached to the back of the unit and it is different than the 2006 control panel, so I could not just swap it out to see if the control panel was the source of the problem.

Since we were camped for three weeks I spent free time trying to figure out the source of the problem...

Symptoms:
(1) Outside temperature is hot... unit operates with few if any resetting. The time the propane flame is extinguished is on a cold starting and needs numerous check light restarts to get the unit to operatre.
(2) On the first electronic ignition the propane burns blue and well.
(3) When the unit fires up, there is a "boing" sound that seems to be mid center of the ammonia coils, but there are no sensors that can be seen. The propane blue flame is then out, as the gas solenoid valve closes.
(4) After the On/Off and Check Light resetting some heat is generated above the flame and this heat seems to cause the unit to operate until a future automatic sensor triggers the propane to reignite and cool the system.
(5) The burner and Flue Tube are clean. The two fuses appear to be fine in the Control Panel.

The 2008 Gas Equipment Assembly does not have a Thermocouple, although the hole is provided for one. My 2006 has a Thermocouple in that spot. (The ignitor glows yellow and reignites the propane if you manually use the shut off knob on the burner module... additional note.)

If in the trailer you will hear the ignitor light the flame and you will hear the "boing" and the check light comes on, needing to go through the On/Off numerous times to get the system to operate.

There is a temperature sensor that is clipped onto the metal fins beneath the freezer compartment. I suspect that could be the or a source of my problem, but have no way to check.

The manual speaks of a "limp mode" but this does not seem to operate, if that is a clue. That would be better than having to constantly checking to see if the "check light" is on and having to reset numerous times to keep the propane side of the operation operating.

Has anyone encountered this before and have a suggestion?


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Old 05-10-2014, 05:18 PM   #6
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One... last attempt and I give up on home repair!

I removed the Burner Jet and it was clean. Just in case I wanted to clean the very small jet (43 embossed on the part) and so put it under my binocular microscope and judged its diameter. An extension cord I had I was putting on a plug and took a clipping of one of the wires and pulled a single copper "hair diameter" wire out and led it through the backside and pulled it through... no clogs, no dirt... clean. Even under the scope... no change.

I removed the Solenoid Valve from my 2006 that needed to be repaired by warranty (weld break as discussed on the first post), swapped it out with the 2008 model... no change. Same symptoms.

The spark electrode and I guess now, also the thermocouple fires up the burner flame on the first spark... and it sparks about six times or so and... the flame goes out. Turn the frige off, and then on and after a few times it would stay lit. Once it stayed lit the first attempt. But still, no progress is figuring out why it goes out. As I said before, the 110volt part of the unit works perfectly.

I found an earlier posting by Landrum who was having a similar problem and asked about where is the thermocouple on the newer units. The original 2006 unit DID have one. The Board "boxes" are also different, so I can not swap them out to see if it is the board. But.... I reread a comment made by Landrum about the spark probe needs to be IN the flame. Mine was "near enough to spark ignite the propane" and I have never had to do anything on this fridge until now... so I gently took the bracket that holds the ignitor and bent it so slightly to put it ... into the flame.

Since we have been cleaning out the trailer from out last camping trip... the wife coated the linoleum floor and I am anxiously waiting for it to dry and test out the adjusting of the ignitor/thermocouple being over and in the top of the flame. As soon as I have this... my last option... checked, I will post my findings.

I note that Landrum in his 01-02-2014 Post that he did not say if it solved his question or not. So I have some optimism... but after trying most everything else I could see that could "physically go wrong" and not "in the black box"... I will reserve any sense of FIXING the problem until it works.
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Old 05-10-2014, 05:49 PM   #7
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When I adjusted the thermocouple/ignitor so that the tip was in the flame it fixed my problem. Before that adjustment my frig would spark and light the gas immediately, but then it would shut down. Since the thermocouple wasn't hot enough the control board thought there was no flame and shut the gas off.
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Old 05-10-2014, 07:14 PM   #8
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Thanks for clearing that up. If you hadn't had success with that, one of the few things left was to replace the board.

I don't really know if this applies to your year, but the original ones do have a reputation for going bad, or intermittently failing. Alligator (or is it Crocodile?) brand boards are well-known for 'best' quality boards.
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Old 05-10-2014, 07:17 PM   #9
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Dometic RM2551 WORKS after "bending" electrode bracket

I am happy that I was able to use the AirForums to make my problem known and two Forum Members were able to point out some directions.

(1) When Landrum mentioned that the Spark Electrode is also the Thermocouple that was one answer I needed. The manual shows a DIFFERENT unit with a separate thermocouple.

(2) I then found Landrum's original post having a similar problem with his RM2551.

(3) Landrum mentioned about he felt he could have, without knowing himself, made the Spark Electrode/Thermocouple move out of position. (Now I think it was mounted wrong at the factory.)

(4) When he put the Spark Electrode (SE/T) INTO the flame from the Burner Tube... he did not say on his original post if that solved the problem or not. So I felt, after doing everything else, there was nothing to lose by taking the "metal bracket" and taking a pliers to the outside edge and slightly bend the bracket so the tip of the SE/T INTO THE TOP OF THE BLUE FLAME. This was possible without removing the metal screw holding the SE/T to the housing OR bending the electrode itself, which probably would have broken.

(5) After owning this warranty replaced RM2551 after my 2006 had a weld break releasing the ammonia cooling gas and was not repairable. I kept the warranty parts and replaced the entire fridge with the current 2008 model and retained the warranty parts for future repairs... if EVER NEEDED. Well... they may have been needed, but the 2006 Black Box is not similar to the 2008 version, nor some of the parts. The Gas Equipment Assembly is identical, except the 2006 has a separate thermocouple.

WHAT I DISCOVERED IS THAT THE DOMETIC FACTORY SHIPPED THESE UNITS OUT WITH A NEW ELECTRODE AND DOUBLED AS A THERMOCOUPLE, unlike the 2006 two part system, AND THEY WERE MOUNTED AS THE 2006 SYSTEM.

I inadvertently discovered for the FIRST TIME SINCE I OWNED THIS UNIT is that the ignitor sparked ONCE, the Burner lit and it remained ON. I always believed that the Spark Electrode was designed to spark 8 to 10 times, even though the flame was lit on the first spark. This was the first time I watched the spark and silence. No continuous sparking. No Check Light on.

Now. I am cautiously claiming this was THE FIX. I am letting the unit run on propane and will monitor its progress. If the Check Light is on, I will be then have to take it into the local Dometic service representative for .... repair. At a cost to me. If this simple correction FIXES my understanding how these work... Dometic owes a lot of owners refunds for repairs that were not necessary.

It was a new unit and we would blame a gust of wind blowing the burner flame out. We tried to rationalize how and why. If this is the FIX... I hope everyone who has had theirs "repaired" realize this was just a minor bending of the bracket to force the 2008 models INTO the top of the blue flame. Not something you did while traveling...

I know this is a lengthy group of posts for this problem. I have spent hours over the years, in all hours of the day while camping with the On/Off and Check Light resets. Sometimes two resets, sometimes 12 resets to have the unit remain working. I am thankful it seems to have started on the first and only spark and not needing numerous sparks while the flame was lit... it was all unnecessary.

I WILL keep posting my progress on this problem. Dometic's manual is WRONG as the parts ARE not the same. Dometic's Spark/Thermcouple is in the WRONG POSITION when purchased since it uses the older 2006 bracket and requires being IN THE FLAME, NOT JUST NEAR IT TO OPERATE.

Our last camping trip was cut short a week, as we would be awakened at night two to three times with the Check Light needing to restart the unit for the entire time we were camped. This was increasing over the years, but was before, tolerable and less often. It would quit while moving. We considered driving from Hanksville, UT to Salt Lake City, UT to have this fixed, once and for all. But dumped our fresh water and headed home and I said I would figure this out at home... or will take it to a service provider and PAY whatever to solve this... Thanks to Landrum... his headache solved mine... I hope. Thank you.
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Old 05-10-2014, 07:24 PM   #10
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Good luck, Ray!
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Old 05-10-2014, 07:32 PM   #11
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Dometic RM2551 misplaced thermocouple???

Dave Swenson gave Landrum the advice to "move the electrode" as it was also the thermocouple into the flame.

Now, everyone who provided parts of the puzzle have been named.

Since the factory installed RIGID FIXED METAL bracket prevents the SE/T from where it should have been in the 2008 version of the RM2551, any rational person looking at it would find no reason to BEND the factory bracket. Such a simple solution but not obvious as the unit limped along for years...
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Old 05-11-2014, 12:36 PM   #12
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So far, so good....

I am a bit surprised to find the fridge... working without constant resets. This one small bending of sheet metal getting the Spark Electrode/Thermocouple directly over the blue flame of the Burner Tube appears to be the solution.

The fridge is running +5F to -8F in the "ice box". The interior is a consistent +40F.

Since I thought moving the temperature sensor, that slips and slides on the metal fins in the fridge, was also something I was playing with to keep this thing running... the wife noticed it was "not where it should be". She moved it to the furtherest RIGHT FIN and DOWN. It is now at +39F. She wants it at +37F. You know, to keep her wine and my beer cold. Important when you are camped in the Mohave Desert looking for rocks.

The temperature adjustment is rather primitive on the RM2551 and probably ALL of those with no control to change. The temperature is changed inside by moving the "temperature sensor clip" to other metal fins (ours is now on the RIGHT fin) and up or down (ours is way down, if not at the bottom). Down to cool the interior or up to warm the interior and freezer "ice box".

I read that "rough roads" can mess up your fridge and sensors on the Forum. We travel less asphalt highways and more non paved roads. You cannot tell me that the Dometic is built for RV Park and smooth roads... and cannot handle gravel or irregular surfaces. If that is the case... I would be extremely bothered by that excuse for a high priced, simple system. Even a weld should not break on the ammonia piping... EVER. I would then WANT what the US Military uses... like $1,000 toilets... the Dometic already is in that category and should be designed for the rough and ready uses it was intended. I just ask that the unit be set up at the FACTORY correctly. Even the newer manual that the RM2551 uses has the burner system "backwards". I figured it out, and it is not that important, but is flipped from the 2006 manual.

When I stick my head into the AS doorway and the Check Light is not lit... I can finally plan on having a good nights sleep without standing in my shorts, pressing On/Off numerous times at midnight, 3AM and 6AM. I would roll over in bed and squint to see that "stinking check light lit... again"!

So, fellow AS and Other Brand trailer owners with a RM2551 series I hope that my pain helps solve yours.

Synopsis of Propane operated units since 2006:


Propane Oven/Cooktop: 100% perfect
Furnace: 100% perfect
Air Conditioning unit: 100% perfect
Hot Water Heater: 100% perfect
Dometic Fridge: 50% headache prone and "sensitive to vibrations?" (The 2006 under warranty replaced the weld break on the ammonia tubing, so it was 100% and then 0% functional.) The 50% is the 2008 unit and the Check Light and shutting down chronically for more than half of its installation.

My last post will be to report that our temperature gauge will get the +37F internal temperature (in an empty fridge). All this time I though it WAS wind or dust or OUR doing something created this chronic and worsening headache. Maybe it was not the rough roads, dust, wind, bad propane, air in the system, propane leak(s), perfectly level trailer, elevations above 4,000 feet, faulty temperature sensor, spark ignitor was weakened... and on.

This might seem a bit long for a fridge problem. But, I wanted to find someone with a similar complained who was "fiffed" as I to the cause. This simple solution might be all of your cures with the... Check Light demon from Hades.
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Old 05-11-2014, 04:01 PM   #13
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My wife moved the thermostat to the third fin from the right and moved it down to the bottom and has +38F in the interior. She is now happy.

As an added note:
May 17, 2011 she called the 888-867-4188 Tech Service & Warranty at 2:15PM on the RM2551 that was installed by Camping World August 21, 2008 at a cost of $160.00.

She was given these three problems to check:
1- Board
2- Re Ignitor issue
3- Electrode issue
(4)- Maybe NOW someone at Dometic could mention the "factory position of the thermocouple/ignitor (most trailer owners are hands on when it comes to repairs)

I END my ordeal. If anyone has a further question... I will respond when I check any additional posts.
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Old 06-06-2014, 07:30 PM   #14
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This Repair did the Job!

Returned from our trip to Las Vegas, Nevada, staying at the Sam's Town Casino RV Park after two weeks on the move. One week in Las Vegas and another week dry camping in Nevada and Wyoming. I am now leaning more into the enjoying the Full Hookup and Las Vegas entertainment over Rockdocking now.

Highs in the 100 to 110 F. Lows in the 80's. The refrigerator worked perfectly.

... but the Dometic Air Conditioner quit working after four days in the 100F+ days. I adjusted the thermostat for 15F degrees below the current temperature. The fan operates, but the air conditioner compressor attempts to start but then quits. It started at the same time a hot electrical smell was noticed. Maybe the starting capacitor... I do not know... so I am now going to troll the Air Conditioner problems.

Always something to learn.
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