Dometic RM5380 fridge won’t stay lit on gas

[robdav]

Hi Again

 

This is similar to a previous post I made on behalf of my sister’s van but I don’t think it’s the same problem as ours because ours has worked for a couple of years with no problem. In the end the dealer tried two fridges and eventually told her it was down to a vent problem??!! It has been fine since.

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Dometic-RM5380-fridge-runs-on-gas-for-15-mins-or-so-then-stops/51518/

 

Our fridge works fine on electric (and I think battery but I never use it). It used to work perfectly on LPG but recently has become very unreliable. It’s less than three years old. It ignites fine but runs for variable amounts of time before cutting out. The time it runs for seems to have got shorter. This morning it ran for 10 mins then went out.

 

I have tried the obvious i.e., cleaned the burner and flu and it all looks fine.

 

According to Dometic, the burner part number for this fridge is 289060489. Googling for the best online picture gets me here:

 

https://www.huoltopalvelu.com/Dometic-gas-burner-289060489

 

Obviously, I need to check the gas jet but my question is where does this sit? Attached is a photo of my burner with the gas inlet coming in from the left.

 

I have tried detaching the silver nut on the left (where the red sealant is) with the brass nut labelled ‘65’ but stopped and thought I would ask before proceeding.

 

According to this UK link (closest I can find but not the same part number, might be because it includes the thermocouple?) it uses a KZ16 jet.

 

Burner - https://caratech.co.uk/collections/dometic/products/caravan-motorhome-dometic-fridge-burner-rm-l9435-2890604917

 

Jet above link mentions - https://caratech.co.uk/products/caravan-motorhome-dometic-fridge-gas-jet-kz-16-rm-7-8-series-2890483114?_pos=2&_sid=8251cd1b1&_ss=r

 

I’m not convinced this is the correct jet.

 

Has anyone had any experience cleaning the jet on a RM5380 fridge please or other ideas?

 

Thanks

 

Rob

[robdav]

So I got the jet out and have cleaned it up with some brake cleaner but it still won't stay lit. I have attached an after shot of the jet.

 

So I might try replacing the jet and then the thermocouple?

 

Any more ideas?

 

Thanks, Rob

[Keithl]

Try lighting ALL the burners on your gas hob and see if they stay alight. You may have a failing regulator.

 

Keith.

[robdav]

Hi Keith

 

Gas hob burners all working fine all at once no problem.

 

Thanks

 

Rob

[thebishbus]

I had an intermittent problem with ours. I moved the tip of the thermocouple into to a different part of the flame, that solved the problem .

Brian B.

[Ocsid]

A long shot, but easily checked.

First is it a fridge that requires the gas knob pushing in, if so this is worth a try?

 

Is the flame failure device being fully set?

 

I have had myself and known another suffer from the front facier panel not allowing the gas valve to be fully pushed in.

I is easy to see if the knob "grounds" on the panel.

 

If so remove the knob and push the shaft in without the knob fitted when igniting.

 

All, we did to fix it was to pull off the knob, put a very small bit of cringed up aluminium foil in the knob and put it back.

[robdav]

thermocouple is well and truly in the flame I think as it's getting red hot as per photo.

 

It doesn't require the gas knob to be pushed in to remain operating, only to start it.

[Derek Uzzell]

For the Dometic RM5380 model of fridge, isn’t gas-ignition via an AA 1.5V ‘torch’ battery?

 

If that’s correct, have you checked the charge-state of that battery?

[robdav]

Hi Derek

 

I believe it is, I haven't had the fridge out yet to check but I did find this poor chap who looks like he had fun discovering this!

 

 

The fact that the fridge lights first time made me discard this.

 

Do you think the battery is used for subsequent lighting of the burner when it's running (or should I say when running on gas)?

[Robinhood]

robdav - 2021-04-27 6:38 PM

 

Do you think the battery is used for subsequent lighting of the burner when it's running (or should I say when running on gas)?

I'm pretty confident that the battery is used only for initial lighting. The fridge has flame-failure detection (thermocouple) which will inhibit the gas if the flame goes out, but no automatic re-ignition.

 

The Youtube clip amuses me; The battery can indeed be very rather difficult to remove - but there is a knack (which I think I've posted about on here before) and it doesn't involve vandalising the fascia ;-).

 

My first suspicion would be the flame-failure device (thermocouple), though 10 mins running might be a bit long to really support that.

[robdav]

I'm leaning towards it being the thermocouple as well.

 

From cold it runs for 10 mins or so. If I then repeatedly re-light it, the time shortens so I’m wondering if this is temperature related.

 

I’m not quite sure how a thermocouple works so not sure if/why they fail/deteriorate over time.

 

Just got to try and get one now, can only find them on European websites like this one

 

https://www.campingwagner.de/product_info.php/info/p66708_Kit-Thermoelement---Dometic-Ersatzteil-Nr--292343591---fuer-Dometic-Kuehlschraenke-RML-8230.html

 

Better find your 'battery removal' link though just in case!

 

Thanks.

 

[Robinhood]

I don't think the thermocouple is difficult to source (assuming RM5380)

 

This is just an example:

 

https://www.leisureshopdirect.com/cooling/caravan-fridge/dometic-caravan-fridge-spare-parts/dometic-thermocouple-length-1400mm

 

10 minutes is a bit of a long time to check, but the usual method of testing is to use the "flame failure override" to defeat the thermocouple function and see if the flame remains lit (usually involves holding a knob in - as you do when lighting). If the failure interval is shorter after the first 10 minutes, then you might check this on subsequent relighting. Time consuming but a reasonable indicator. You might be able to wedge it.

 

Battery link here:

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Fridge-wont-light-on-gas/54513/

[robdav]

Thanks Robinhood.

 

Will try the override method tomorrow.

 

That appears to be a different thermocouple to the one fitted. The part number I have is 292343591 but waiting for Dometic to confirm, it looks different to the regular ones on sale on UK sites.

 

[Robinhood]

The one I've listed has RM5380 in its description, but it does look slightly different to your picture.

 

If you do try the override method, then take care, as you are effectively nullifying a safety device. If it were me, I'd want to wedge it (or have someone else hold it in) and observe the flame directly (through the vents). If it stays lit (longer than currently), then the thermocouple is certainly suspect. If it goes out as it has been, then the thermocouple is probably OK, and you need to unwedge or stop pushing the button asap, as gas will still be flowing.

 

The thermocouple works by containing an expanding liquid or gas (I'm not sure it's still mercury) which expands under the heat of the bulb being in the flame, and the expansion is used to operate a switch via a plunger at the other end of the copper coil. Failure is often absolute (via leakage or the bulb not being in the flame) but it is conceivable that, if it is "on the edge", the contents will initially expand and function properly, but then the metal itself will subsequently expand, and the increased volume will cause the pressure to drop again, and the switch will be withdrawn. (Theory, but it seems OK to me).

 

Edited to add:

 

This looks more like your picture, and shows RM5380 as fitted (this is an example, there may be cheaper listings out there)

 

https://www.inter-spares.co.uk/electrolux/electrolux-dometic-caravan-fridge-spare-parts/rm5310/thermocouple-en-12.html

 

 

[robdav]

I’ve found a few parts today that mention they are suitable for an “RM5380” but aren’t. One supplier said this to me today “Hi , SORRY , but the RM5 series is a bit rare , we do not have data on that one”

 

Understand the warning about the ‘override method’, will try it tomorrow as don’t want to buy a new thermocouple if it’s not going to fix the problem.

 

Thanks for the thermocouple explanation – interesting.

[Robinhood]

robdav - 2021-04-27 8:47 PM

 

Thanks for the thermocouple explanation – interesting.

...well, what I've described is not technically a "thermocouple".

 

A thermocouple would use the different electrical effects of temperature on different metals to generate a current, and it is possible to use such a current to electrically operate a flame failure device.

 

Looking at the size of the copper capillary on your version, I'm taking a leap of faith that it is the pressure operated type (but I may be wrong).

 

Grove Products (a major spares dealer) website note a 2200mm version for the 5310 (same model series as the 5380) and the one I've last listed above is 2200.

[Keithl]

Robinhood - 2021-04-27 8:29 PM

 

The thermocouple works by containing an expanding liquid or gas (I'm not sure it's still mercury) which expands under the heat of the bulb being in the flame, and the expansion is used to operate a switch via a plunger at the other end of the copper coil. Failure is often absolute (via leakage or the bulb not being in the flame) but it is conceivable that, if it is "on the edge", the contents will initially expand and function properly, but then the metal itself will subsequently expand, and the increased volume will cause the pressure to drop again, and the switch will be withdrawn. (Theory, but it seems OK to me).

RH,

 

I believe that a Dometic thermocouple is actually an electrical device rather than a mechanical.

 

When the thermocouple tip is warmed it creates a very small electrical current (possibly 30 - 40 millivolts) and this then powers a solenoid coil which holds the valve open. When the thermocouple tip cools the voltage drops and the coil is released.

 

See this MH Fun post... https://www.motorhomefun.co.uk/forum/threads/how-do-you-test-the-fridge-thermocouple.202095/

 

Keith.

 

Edit: Looks like I crossed posts with your last post.

[Keithl]

This thermocouple is listed as fitting an RM5380 and to me looks like the electrical variety, it appears to have insulation between the two metallic parts at the gas valve end...

 

https://www.leisureshopdirect.com/cooling/caravan-fridge/dometic-caravan-fridge-spare-parts/dometic-rm6270-absorption-refrigerator-spare-parts/dometic-thermocouple-length-1400mm

 

Keith.

[Robinhood]

Yes, it wouldn't surprise me - it's a long time since I replaced one :-S (and the terminology rather got me wondering after I'd posted).

 

I'm still not fully convinced looking at the tube size and the termination, but it wouldn't surprise me if it were a real "thermocouple".

 

Similar theory applies, though - if it is "on the edge" then it might work for some time, then drop out (and the method of testing is still valid).

 

...and that's the link I posted above, Keith, but the "flame end" doesn't look the same as the OP's. (The later Inter-Spares link is a better match).

[Alanb]

robdav - 2021-04-27 7:19 PM

 

==================================================================================

 

I’m not quite sure how a thermocouple works so not sure if/why they fail/deteriorate over time.

 

==================================================================================

There are two basic types of flame failure device in common use that are called thermocouples.

 

The true thermocouple is a thermoelectric bimetallic junction device, which produces a small electric current when heated. This current is used to energise an electromagnet which latches the gas valve open. In this type the electrical connection is concentric (coaxial?) with the outer conductor being a copper tube of about 3mm diameter.

In a recent thread relating to gas hob problems, advice was given to try slackening, and retightening the connection at the gas valve, to ensure a good electrical contact.

 

The second type of device is an ether, or similar volatile liquid filled bulb, permanently attached to a gas valve via capillary tubing. The pressure of the ether vapour is used to latch the gas valve, or otherwise maintain the gas supply via a small bellows. If the ether leaks out, a complete new valve is required.

 

I think that we have both types fitted to our domestic gas hob and oven. The ether type on the hob operate almost instantaneously, while the thermocouples on the oven and grill take a lot longer to latch.

 

Many years ago we had a gas water heater, which had a pilot flame lit 24/7. There were some failures of the thermocouple, due to it being eroded by the pilot flame which it monitored.

 

A previous gas oven, with ether bulb type of flame failure device suffered from swollen (burst?) ether bulbs in its early life. The oven manufacturer eventually adopted a different make of bulb. End of problem.

 

Alan

[Derek Uzzell]

Dometic Installtion and Operating Manuals that cover the RM5380 appliance can be found here

 

https://www.dometic.com/assets/12/10/dometicrm53xx_inm_4445102229_emea(en-de-fr-nl)_2021-03-30_81210.pdf

 

https://www.dometic.com/assets/23/71/operating%20manual_52371.pdf

 

(Replacing the gas igniter battery is dealt with on Pages 7 and 24 of the 2nd link.)

[Robinhood]

robdav - 2021-04-27 8:47 PM

 

I’ve found a few parts today that mention they are suitable for an “RM5380” but aren’t. One supplier said this to me today “Hi , SORRY , but the RM5 series is a bit rare , we do not have data on that one”

Whilst it isn't entirely conclusive, the document here:

 

http://www.groveproducts.co.uk/medias/documents/grove/cata/Z-%20SPARES%20DOMETIC.pdf

 

gives exploded diagrams of the RM5310 and RM5330, (same series as the 5380) both of which use the same 2200mm thermocouple part number. That p/n also resolves to the inter-spares link I posted above, with a RM5380 endorsement, and a picture that looks encouraging.

 

If I play on Google a bit I can get a few other (cheaper) hits which also mention RM5380, but none, alas, cheaper (and in stock).

 

At the price quoted, it would certainly pay to try to convince yourself that's where the problem lies, as it's hardly at a cost that encourages the "worth a try" approach..

[robdav]

Agreed, cost a bit higher than "worth a try" approach. I will try the ‘override’ option this morning when I’m working in the van to try and prove if worth buying a new one.

 

I’m hoping Dometic will confirm part number with me today. I received the attached part number yesterday which only seems to be a bump of the last digit from the part number in the Grove Products document.

 

Will update later. Thanks again for all the input.

[robdav]

I can vouch for robinhood’s Blue Tack method for changing the gas igniter battery – very simple once you know about the slight depress and 90 degree turn to the left.

 

I tried the ‘override’ test by the first use of an adjustable selfie stick (wedged to the other side of the van, almost purpose made) to keep the gas button pressed in.

 

Alas the burner extinguished after about the same sort of time. I checked the button was pressed in by only having to press the igniter button for the burner to light again. I tired it a few times but no luck in continued operation.

 

What would be the next step in diagnosis, any ideas?

 

[Robinhood]

Just to be sure - it's the flame-failure override process you need to invoke. That is by keeping depressed the knob that you need to when lighting on gas (which I think is the temperature control on that fridge).

 

If that's what you're doing, the likelihood of it being the thermocouple is somewhat reduced (if not entirely eliminated), and it is something more fundamental.

 

Just a thought, though - are you running on propane or butane? There's just the passing chance (clutching at straws a bit) that cold temperatures could be affecting the gas pressure at the moment, if running on butane.