Another Gas Fridge Problem! (1 Viewer)

DBK

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An alternative title to this Thread could be "Convince me I don't to spend £150" :).

Here's the problem. One for the fridge experts.

Anyone who has followed my trip reports over the last couple of years might recall we have had intermittent problems with our Dometic RM3510 manual three-way fridge when running on gas. The initial problem was getting it to stay alight once lit. We worked out if we let it cool down for twenty minutes after running on electric it would light and stay lit.

Then on this trip we have experienced three occasions when it wouldn't work properly on gas. It would light and stay lit but it didn't cool things effectively. The top of the flue was hot but the fridge temperature wouldn't go much below 16°C. The fault was not permanent and cleared itself if we left it switched off overnight. The first two times this happened we were on aires so were unable to use EHU.

Two days ago I made a sort of diagnostic breakthrough by discovering the flame was lighting but only staying at the low level state. My understanding is the thermostat controls the temperature by switching between a high and low flame.

Further evidence is the last two times I have lit it after an overnight rest I can distinctly hear a gentle roar from the flame which I couldn't when lighting it in its failed state. The fridge would then run perfectly on gas. The first two times also happened after a day of driving on very rough roads and steep hills making me wonder if the fault might be the refrigerant was getting "mixed up" somehow but the last time it failed it was after a day of gentle driving and it began to work as soon we were on EHU and the fridge switched to mains. So I think the failure after the rough roads was just coincidence. The fridge was also level on each occasion.

My suspicion is the gas thermostat valve is failing. This is a picture of the beast.

31Zyz3FrhGL.jpg


There is a little electrical meter on the front of the fridge with a needle which swings across into a green zone when it is operating on gas. It may be relevant to the fault diagnosis that when we first bought the van the needle shot across very quickly into the green zone. These days it only moves very slowly and only just into the green zone.

Now to the alternative title for this thread. :). I've found a UK supplier of this valve but it is (gulp) £150 although a German supplier is offering them at €140 so if the shipping cost is reasonable I know who I will go to.

It is now running well on gas after a night on EHU - I intend to keep it on gas until we board the ferry! We also have an electric coolbox so we have not suffered from warm beer while the fridge was playing up.

So, here's the question: Do you think replacing this valve is the way forward or can anyone think of any other cause for the faults we have seen?
 
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Feb 9, 2008
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I am aware of several failures when on gas and all down to a dirty flue, causing the heat exchange to be significantly reduced. I had a failure on mine too whereby no alarm or warning with a good flame but the fridge suddenly refused to cool. Once the flue was cleaned the problem was solved. You may want to check this before splashing the cash.
 
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DBK

DBK

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I am aware of several failures when on gas and all down to a dirty flue, causing the heat exchange to be significantly reduced. I had a failure on mine too whereby no alarm or warning with a good flame but the fridge suddenly refused to cool. Once the flue was cleaned the problem was solved. You may want to check this before splashing the cash.
Thsnk you, I forgot to mention I have checked the burner and flu and they are clean. If the flue was blocked it would consistently not work well I think. My fridge works fine on gas - but only after it has had a rest. :LOL:

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deleted-member02

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Then on this trip we have experienced three occasions when it wouldn't work properly on gas. It would light and stay lit but it didn't cool things effectively. The top of the flue was hot but the fridge temperature wouldn't go much below 16°C. The fault was not permanent and cleared itself if we left it switched off overnight. The first two times this happened we were on aires so were unable to use EHU.
I've experienced this a few times over the years, always after using the fridge continuously for more than a week or two.
I've been told that the fridge can work too efficiently, causing the gubbins to freeze and stop cooling (technical description :))
By leaving it off overnight, the rear can defrost, allowing it to start working again the following day...
Perhaps related to your problem?
 
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DBK

DBK

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I've experienced this a few times over the years, always after using the fridge continuously for more than a week or two.
I've been told that the fridge can work too efficiently, causing the gubbins to freeze and stop cooling (technical description :))
By leaving it off overnight, the rear can defrost, allowing it to start working again the following day...
Perhaps related to your problem?
Interesting thought, thank you. It does work reliably on mains but perhaps the cooling (and freezing) effect is greater on gas?
I'm playing with the fridge thermostat setting at the moment to get it to a reasonable temperature inside. It was exactly 0°C this morning in the middle of the fridge after a night on EHU which is a bit chilly as it is full of salad stuff. It's now running on gas and after a bit of twiddling the middle of the fridge is around 4°C which is about right.
I'm using a remote sensor from a cheap weather station to measure the temperature. :)
 
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deleted-member02

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Interesting thought, thank you. It does work reliably on mains but perhaps the cooling (and freezing) effect is greater on gas?
I'm playing with the fridge thermostat setting at the moment to get it to a reasonable temperature inside. It was exactly 0°C this morning in the middle of the fridge after a night on EHU which is a bit chilly as it is full of salad stuff. It's now running on gas and after a bit of twiddling the middle of the fridge is around 4°C which is about right.
I'm using a remote sensor from a cheap weather station to measure the temperature. :)
As I understand it, gas is the most efficient way of cooling.
If it's not cooling, the obvious action would be to turn it up. Apparently 'less is more' in this case, turning the thermostat down is more beneficial. Our thermostat is set between 2-3 and keeps the fridge around 4°c.
Monitoring fridge temperature remotely - that would be a nice addition to motorhome 'tech' (y)

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Feb 21, 2016
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Beat me! Turned ours down and it seemed to work better.
 
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DBK

DBK

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Beat me! Turned ours down and it seemed to work better.
It is is turned down to almost minimum now and still only just above freezing. Looks increasingly like the thermostat is goosed. :(
 
Feb 21, 2016
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It is is turned down to almost minimum now and still only just above freezing. Looks increasingly like the thermostat is goosed. :(
Sorry,maybe I’m being thick,but earlier you said 4 degrees was about right,so just above freezing is ok isn’t it?

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Aug 6, 2013
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It is is turned down to almost minimum now and still only just above freezing. Looks increasingly like the thermostat is goosed. :(
I'd agree. From your description it's the same as a Thetford fridge l had a lot of trouble with in my last van caused in the end by an incorrect burner being fitted prior to my ownership. There are 3- and 4- slot burners available. Mine was 4 and should have been 3. Symptoms were similar to yours. Incidentally the meter thingy reads the voltage generated by the FFD thermocouple so how high it goes depends on how hot it gets.
 
Feb 21, 2016
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I'd agree. From your description it's a Thetford fridge. I had a lot of trouble with mine in my last van caused in the end by an incorrect burner being fitted prior to my ownership. There are 3- and 4- slot burners available. Mine was 4 and should have been 3. Symptoms were similar to yours. Incidentally the meter thingy reads the voltage generated by the FFD thermocouple so how high it goes depends on how hot it gets.
Dometic.
 
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Is this the part you want?

http://www.caravan-components.co.uk/Thetford-Fridge-Manual-Gas-Valve-Version-2-and-Thermostat

A bit cheaper at GBP 62

I had to search for a part for our fridge and did it thus...

On Google type in your product name (sometimes pays to keep it to as few relevant words as you can)

In your case I typed "Dometic RM3510 gas thermostat valve"
When the results come up, select "Images" see below...

Untitled.jpg


Scroll through the images until you find a match and then click on "Visit" which will take you to the site that included the image.

Untitled 2.png

Probably 8 in 10 will be a waste of time but you might strike lucky and find the part listed on a small time or even international website that doesn't load in the first few pages of Google if you simply search, for say, " Dometic RM3510 gas thermostat valve for sale"

Hope this helps

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DBK

DBK

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Is this the part you want?

http://www.caravan-components.co.uk/Thetford-Fridge-Manual-Gas-Valve-Version-2-and-Thermostat

A bit cheaper at GBP 62

I had to search for a part for our fridge and did it thus...

On Google type in your product name (sometimes pays to keep it to as few relevant words as you can)

In your case I typed "Dometic RM3510 gas thermostat valve"
When the results come up, select "Images" see below...

View attachment 237446

Scroll through the images until you find a match and then click on "Visit" which will take you to the site that included the image.

View attachment 237448
Probably 8 in 10 will be a waste of time but you might strike lucky and find the part listed on a small time or even international website that doesn't load in the first few pages of Google if you simply search, for say, " Dometic RM3510 gas thermostat valve for sale"

Hope this helps
Many thanks for that. It is a Dometic fridge but that much cheaper Thetford links looks exactly the same part. :) I got the £150 quote using an image link but I only looked at a couple. It may be safest to remove the thermostat and send a photo to the supplier and ask if what they have is identical.
 
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DBK

DBK

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Sorry,maybe I’m being thick,but earlier you said 4 degrees was about right,so just above freezing is ok isn’t it?
I may have misled you. :) When it isn't working properly on gas, despite being lit, the internal temperature was typically in the teens. It now seems to be running with a full flame but I'm not sure it is being regulated correctly. The photos below might help to explain this.

DSC_0342.JPG


In the above the thermostat is turned almost down to minimum but we have never had to turn it down this far before. Even so the internal temp in the fridge is now cooler than I would like.

DSC_0343.JPG


The upper temperature shown above is the ambient temperature.

I can live with the present situation for this trip. It is running on gas and if I don't turn it off we should be fine. :)

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DBK

DBK

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I'd agree. From your description it's the same as a Thetford fridge l had a lot of trouble with in my last van caused in the end by an incorrect burner being fitted prior to my ownership. There are 3- and 4- slot burners available. Mine was 4 and should have been 3. Symptoms were similar to yours. Incidentally the meter thingy reads the voltage generated by the FFD thermocouple so how high it goes depends on how hot it gets.
But it has worked fine in the past. The problem seems to be intermittent, working one day but not the next .
 
Aug 6, 2013
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But it has worked fine in the past. The problem seems to be intermittent, working one day but not the next .
I wasn't suggesting that the jet was the problem. I think you are correct to consider the gas valve.
 
Feb 21, 2016
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Got it!

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DBK

DBK

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Update on progress so far. :) After a lot of head scratching I have discovered the fault - or at least hope I have. There is an intermittent connection in the selector switch, the thing which manually selects gas or electric. I've stripped the switch down and thoroughly cleaned it internally but sadly this doesn't cure the fault. I know which contact set is the problem because if I remove the two wires from them and join them with a bit of wire the fridge works perfectly. I've even removed the contacts (fiddly) and cleaned them but this didn't help either. The problem may be either the body of the switch is distorted or there is wear in the armature thingy which operates the contacts. If I twiddle the wires or even just squeeze the body of the switch I can get it to work briefly.

So I've ordered a new switch which should arrive next week. Not too expensive (a lot less than a new fridge!) and hopefully this will sort the problem. :)
 
Aug 6, 2013
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Update on progress so far. :) After a lot of head scratching I have discovered the fault - or at least hope I have. There is an intermittent connection in the selector switch, the thing which manually selects gas or electric. I've stripped the switch down and thoroughly cleaned it internally but sadly this doesn't cure the fault. I know which contact set is the problem because if I remove the two wires from them and join them with a bit of wire the fridge works perfectly. I've even removed the contacts (fiddly) and cleaned them but this didn't help either. The problem may be either the body of the switch is distorted or there is wear in the armature thingy which operates the contacts. If I twiddle the wires or even just squeeze the body of the switch I can get it to work briefly.

So I've ordered a new switch which should arrive next week. Not too expensive (a lot less than a new fridge!) and hopefully this will sort the problem. :)
You have just triggered my memory. When l was researching how mine was wired l couldn't understand how the gas was turned off when switching to electric (my Thetford was identical to your Dometic). As the gas & electric temperature control is the same knob it cannot be used to shut off the gas. So a pair of contacts within the rotary control disconnects the flame failure device. The fridge thinks the flame has gone out so it turns off the gas. Probably the pair of contacts that are causing intermittent problems on yours.

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All fixed now. :) There was a delay getting the replacement switch, zero stock anywhere it seemed but www.leisureshopdirect.com sourced one directly from Dometic which arrived after a few weeks.
I was momentarily thrown when it arrived as it was a different colour and had two extra terminals but moulded into the body was a key to what each terminal did and this was the same as the original.
Changing over one wire at a time then wrestling with the wires to get them to fit in the space the fridge is now running perfectly on gas. :)

DSC_0473.JPG


I've learnt a bit how these fridges work in the process but hopefully I won't need any of this knowledge for a while. :)
 
Feb 21, 2016
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“De blue ones connected to the white one,
De white ones connected to the brown one
De brown ones connected to the green one
........Put your trust in de Lord!”

Sorry,maybe had too much sun already today.
:D:D:LOL::ROFLMAO::D:rolleyes:
 

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My fridge was not igniting or even sparking. I expected the burner control module (£120) was the problem. Luckily rather than fork out for one I took it to John's Cross where Ian found it was just a bad connection on the multiplug to the module so saved me quite a bit:)
Unless you're certain of your diagnosis I suggest going to an expert can sometimes be the cheapest way.
 
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