Dometic RM7401 problem on gas. Out of ideas 😒

[chalkstorm]

Hi
Just back from 19 days touring through Poland and down into Hungary. I nearly always don't use EHU and rely on solar and gas.
My Dometic RM7401 has worked perfectly for years on all 3 power sources including gas.
3 days left of the holiday and I notice the freezer contents have thawed and the fridge temperature was not cold.
I've done a few tests and made the following observations.
1 It will chill the freezer down to minus 18 deg C on EHU
2 On 12v it will maintain that temperature
3 On gas, the freezer box would slowly increase in temperature to 0 degrees

I returned home last night and today after much googling and reading posts on here have used some compressed air to last out the burner and the pipe leading to it.

The gas lights and stays lit without issue. It lights with a woosh. I've attached a video. However, regardless of the rotary temperate setting, the flame size does not change.

I have run it today (12 hours) and it has managed to chill it to a minimum of minus 7.4 degs. However the fridge only got to 17.7 degrees (ambient was 26 degrees).

I'm out of ideas now as it works on EHU and 12v.

Anything else I could try? I can get it checked out but won't be till end of September.

Thanks

Si

 

[GeoffnDee]

chalkstorm ,There could be a problem with the helix that sits inside the top of the burner tube/chimney , perhaps it is in the wrong position or damaged causing the problem of not cooling well on gas. ( this part is shown on the cooling page of the parts diagram for the RM7401 , item 102 , part number 2926212206 )

 

[Just smiffy]

Most likely the flue needs cleaning, get to the top of the flue and take out the baffle and some type of bottle brush up and down it will clear it don’t forget to cover the burner so crap don’t block that or best remove it while you clean the flue…

 

[chalkstorm]

Most likely the flue needs cleaning, get to the top of the flue and take out the baffle and some type of bottle brush up and down it will clear it don’t forget to cover the burner so crap don’t block that or best remove it while you clean the flue…

Does the flue just run all the way down to the burner- I won't damage anything by shoving a brush in (I'll cover the burner)? Thanks

 

[PeterCarole29]

I have hard mention before gas regulator clogged/gummed up also the gas valve on the fridge regulator easily changed but the gas valve more expensive i have wondered but never tried if it can be washed out? but think that might be risky, (however if one did was it out and it made the fridge work you could easily then buy the new replacement straight away) as flushing it out with a solvent that may be needed could destroy seals. Please not i,m not suggesting you try unless you are confident working with lpg fittings

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[mitzimad]

just done mine same symptoms look on u tube how to remove the burner assembly and blow the internal gas nozzle out 15 minute job if you can handle a couple of spanners and a screw driver if you want a more detailed account pm me

 

[GeoffnDee]

Does the flue just run all the way down to the burner- I won't damage anything by shoving a brush in (I'll cover the burner)? Thanks

The helix/baffel will need to be removed , and then replaced after cleaning the flue , as it should be found sitting part way down the top of the flue on the end of its retaining wire.

 

[chalkstorm]

Thanks all.

Got home, removed the baffle (which looked remarkably clean), removed the burner (looks clean), bottle brushed the flue from both ends (probably reached the top and bottom third due to length of brush) and nothing much came out of the bottom or stuck to the the brush... blasted it all with air, reassembled, and it's now lit and I'm watching the temperature, see what happens next

 

[Mike800966]

On our 7401 there is a valve which you can think of hi/low ours was stuck in the low position. Engineer just changed it and all ok. If you have cleaned out everything else then that's only gonna help. Don't know if the valve can be mended.
Mike

 

[chalkstorm]

Hi - thought I'd give a quick update....

1. By 08:00 this morning, the freezer had dropped from 30+degrees to minus 14.6 (approx 14 hours)
2. It seemed to stick at this temperature so I turned down the temp dial on the front of the fridge to max
3. The freezer then actually increased in temperature by about 1 degree!
4. I reverted to the normal setting (at about 2/3rds on the dial) but put on the extra fans I have at the top vent - this made no difference
5. I've switched them off and it's stabilised at around minus 13 degrees

My question now is, does this feel like reasonable performance? Note - the fridge and freezer box are totally empty.

EDIT - Mmm the fridge is at 15 degrees - that's not good.... I've bought some heat transfer paste and will check the aluminium plate but how can it be that warm in there

Thanks

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[chalkstorm]

Ahhh sorry - replying to my own post but now think I've taken it as far as I can (again).

1. Freezer was at minus 12.9 and fridge at 15 ish (on gas now for almost 24 hrs)
2. Switched it to EHU and freezer dropped to minus 15.5, but interestingly, fridge dropped to 11 (significant drop)
3. I then switched on my cooling fans (in the top vent), still on EHU and freezer now minus 20 and fridge at 6 degrees. Perfect. You can see where the temperature drops on the graph

So then.... I'm assuming the gas is not hot enough to chill the freezer down any further than it has and then there's nowhere near enough power to filter down into the fridge (fins). I've got cooling paste ready to do that job but I don't think that's the real issue.

2 questions - the GV100 gas valve - is that an on or off only or does it control the gas output/size of flame? If it is on or off only, then it works. What else control the size of the flame? Is there anything else I can check?

Thanks and sorry for the many questions!

 

[Hettie's Crew]

Thanks all.

Got home, removed the baffle (which looked remarkably clean), removed the burner (looks clean), bottle brushed the flue from both ends (probably reached the top and bottom third due to length of brush) and nothing much came out of the bottom or stuck to the the brush... blasted it all with air, reassembled, and it's now lit and I'm watching the temperature, see what happens next

View attachment 793326 View attachment 793327

I would be concerned about the rusty condition of the ascending boiling tube, further up it comes into contact with the flue and they are known to seriously rust there, resulting in ammonia leaking and the termination of the fridge. Serious rusting could be reducing the heat transfer ability between the two.
You could remove the insulation from around the boiling tube to check its condition and maybe ? clean it up and protect it with some heat proof paint.
It looks a bit terminal though.

 

[Basildog]

Sorry if this sounds brutal but in my experience it’s far better to replace the burner with a new one rather than messing around with cleaning them.
I have had a few that I have cleaned then replaced the burner and achieved much better results.
We won’t get involved with fixing fridges as it’s not financially viable, they can be extremely time consuming and by the time we’ve removed them and tested / replaced parts if we can get them in a sensible time frame
Then suddenly we get blamed for lots of other problems in the van .
It’s obviously a different story if doing it yourself as time spent doesn’t matter

 

[chalkstorm]

Sorry if this sounds brutal but in my experience it’s far better to replace the burner with a new one rather than messing around with cleaning them.
I have had a few that I have cleaned then replaced the burner and achieved much better results.
We won’t get involved with fixing fridges as it’s not financially viable, they can be extremely time consuming and by the time we’ve removed them and tested / replaced parts if we can get them in a sensible time frame
Then suddenly we get blamed for lots of other problems in the van .
It’s obviously a different story if doing it yourself as time spent doesn’t matter

Yeah - I could see the financially viable bit with the trial and error approach - at least I can try something and walk away for 6 hours and ,try again. I've got a festival in a couple of weeks so I've put a cheeky feed I can plug in to the leisure battery (although it draws 10 amps!) which should mean I avoid food poisoning until I fix it or change it.

 

[jockaneezer]

Just had a quick look at that GV100 valve online and it has three wires going to it, an earth and two services, so maybe it is a two stage valve allowing for a high and a low gas feed ? Can't find a description for it's operation, but it would fit in with you not getting a decent cooling on gas if the higher flow section isn't working ?
Try giving yours a light tap with a plastic screwdriver handle just to make sure it's not sticking ?

Dometic GV100 Gas Valve with Gas Connection - 241279831 - Otter Mobile Caravan Services

Dometic GV100 Gas Valve with Gas Connection Dometic Part no. – 241279831 – Replaces Part no. – 241279820 This Gas Valve is used in various fridges including the following models RM84XX – RM85XX – RM72XX – RM73XX – RM74XX – RM76XX If the fridge model you have is not listed...

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[chalkstorm]

Just had a quick look at that GV100 valve online and it has three wires going to it, an earth and two services, so maybe it is a two stage valve allowing for a high and a low gas feed ? Can't find a description for it's operation, but it would fit in with you not getting a decent cooling on gas if the higher flow section isn't working ?
Try giving yours a light tap with a plastic screwdriver handle just to make sure it's not sticking ?

Dometic GV100 Gas Valve with Gas Connection - 241279831 - Otter Mobile Caravan Services

Dometic GV100 Gas Valve with Gas Connection Dometic Part no. – 241279831 – Replaces Part no. – 241279820 This Gas Valve is used in various fridges including the following models RM84XX – RM85XX – RM72XX – RM73XX – RM74XX – RM76XX If the fridge model you have is not listed...

ottermobilecaravanservices.co.uk

Thanks jockaneezer. Tried that. I ran the outer ring of my electric drill on the bottom of it to vibrate it too... No difference. In fact, gas is burning... And the freezer has gone from minus 15 to plus 5 in the last few hours (despite the flue being hot... Got 100+ degrees on the tube coming out of the top of the flue).

 

[Basildog]

Thanks jockaneezer. Tried that. I ran the outer ring of my electric drill on the bottom of it to vibrate it too... No difference. In fact, gas is burning... And the freezer has gone from minus 15 to plus 5 in the last few hours (despite the flue being hot... Got 100+ degrees on the tube coming out of the top of the flue).

We had a Thetford fridge that wasn’t sure if it was a fridge or a food warmer.
Sometimes it would work perfectly but every so often it would heat everything up
We have had some great fridges that have worked really well and some others that have been totally useless.
Dometics acceptable temperatures are a complete joke their figures aren’t anything like you would expect.
In fact their figures make the fridge a pretty useless cool box.
That was a brand new one they wouldn’t replace

 

[chalkstorm]

Mine's been good for the last 5 years although granted, I've not examined the actual temperature as much as in the last week

I've tested the heat at the tube before it goes into the cooling fins behind the top vent and it's around 20 degrees hotter on 12v and 240v so definitely gas not hot enough (even though it heats the pipe to 100 degs)

Currently soaking jet and burner in alcohol (although I've already checked and used compressed air). Will leave them overnight and then reassemble...

Bearing in mind the issue has come on quickly, I don't think it's the issue Hettie's Crewe flagged (yet at least but accept this is looming). It's got to be the Gv100 (but gut feel says it's not as I think that's an on/off valve), the burner Control unit or Thermostat control... (although I don't know what this looks like or how it works, but everything works on 240v). Interestingly, last thing I've done while it was on gas was turn the dial up to max and while the flame size did not change, the freezer all but stopped working and temp rose to plus 7 degs!

 

[Basildog]

Mine's been good for the last 5 years although granted, I've not examined the actual temperature as much as in the last week

I've tested the heat at the tube before it goes into the cooling fins behind the top vent and it's around 20 degrees hotter on 12v and 240v so definitely gas not hot enough (even though it heats the pipe to 100 degs)

Currently soaking jet and burner in alcohol (although I've already checked and used compressed air). Will leave them overnight and then reassemble...

Bearing in mind the issue has come on quickly, I don't think it's the issue Hettie's Crewe flagged (yet at least but accept this is looming). It's got to be the Gv100 (but gut feel says it's not as I think that's an on/off valve), the burner Control unit or Thermostat control... (although I don't know what this looks like or how it works, but everything works on 240v). Interestingly, last thing I've done while it was on gas was turn the dial up to max and while the flame size did not change, the freezer all but stopped working and temp rose to plus 7 degs!

As far as I remember there’s no flame control it’s either on or off .
Honestly don’t waste your time cleaning the burner.
If the fridge is working well on other power sources just get a new burner.
The tolerances between working properly or not are tiny , just a bit of rust makes a difference.

 

[chalkstorm]

Changed the burner and jet - absolutely the same. Looks like I'll be ripping it out....

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[chalkstorm]

Mmm.... So, ran it on EHU on the drive then switched it to gas while I'm away at Camper Calling festival (since Thursday afternoon). It's been faultless

 

[chalkstorm]

Mmm.... So, ran it on EHU on the drive then switched it to gas while I'm away at Camper Calling festival (since Thursday afternoon). It's been faultless

 

[ianto999]

The drive to festival dislodged some rust/particle?

 

[Jimbohorlicks]

Mmm.... So, ran it on EHU on the drive then switched it to gas while I'm away at Camper Calling festival (since Thursday afternoon). It's been faultless

Any updates?

 

[chalkstorm]

Hi
I don't think anything was dislodged as it was as clean as a whistle once I'd finished (although I did give it another blast with air and a cloth down the flue). I tested it for a week at home on gas and it was pretty faultless. Off to Ireland at the end of the month so fingers crossed!
Cheers

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[nicholsong]

We have a similar problem with a Dometic RM 6401L 2003 vintage.

Can anyone confirm whether the same solutions posited here for the RM 7401 apply equally to the RM6401 or are they quite different beasts?

Basildog may be able to answer from his past experience.

 

[chalkstorm]

We have a similar problem with a Dometic RM 6401L 2003 vintage.

Can anyone confirm whether the same solutions posited here for the RM 7401 apply equally to the RM6401 or are they quite different beasts?

Basildog may be able to answer from his past experience.

The user manuals and installation diagrams suggest they're very similar (I can't spot any obvious differences) so I'd suspect these solutions may work, or are at least worth trying.

 

[chalkstorm]

I don't think I reported back on this.... after the new jet and burner and me cleaning out the flue (which really had no soot of note in it), the fridge worked beautifully. Back to normal. I used it in October/November, a few times over winter and again this week. I've attached the readings (averaged 2.6 degrees on the middle shelf in the fridge and minus 17 in an empty freezer). Happy with that. However, in my quest to ditch gas, I've been tempted by a compressor fridge (which is in the garage at the moment, while I test the settings and temperatures). Have to say, the 3 way is cooler!

 

[Just smiffy]

Which compressor fridge is it…

 

[chalkstorm]

Which compressor fridge is it…

Dometic NRX130. Just playing around with all the settings. Took the freezer divider out last night and ran it on a quiet night mode - whole fridge is at 2.5 degs this morning. Happy with that. Probably fit it next weekend.

EDIT - The 3 way freezer is a degree or 2 colder, fridge is about the same

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