Thetford fridge not working on gas

Feb 13, 2022
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Arrived on site today and attempted to start on gas to cool quicker. It's the first time I have tried it on gas since buying the van. I should have tested it before as it's now out of warranty. When when I hold the dial in you hear the gas flowing, you press the igniter a few times and you hear it light. Gas indicator changes to "on" position. As soon as you let go of the dial it all shuts off. I suspect thermocoupler. I don't know exactly what version my fridge is but it's in a 2009 Lunar Zenith if that gives a clue? It's all completely manual. Has anyone ever changed the thermocoupler on this or similar? Could the issue be something else?

It's not an issue at the moment as I'm on a Club site with EHU, but I'm planning on a trip to a CL with no EHU end of the month so need to get it sorted by then!
 
Mar 14, 2005
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I can't tell you what model you have just based on the model of caravan. The symptoms you describe certainly point to a problem with the thermocouple, but it could also be a blocked burner which is deflecting the flame away from the tip of the thermocouple.

Being now 14 years old its probably time teh fridge was properly serviced. For safety I suggest you arrange to have it checked out by and AWS mobile technician.
 
Feb 13, 2022
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I can't tell you what model you have just based on the model of caravan. The symptoms you describe certainly point to a problem with the thermocouple, but it could also be a blocked burner which is deflecting the flame away from the tip of the thermocouple.

Being now 14 years old its probably time teh fridge was properly serviced. For safety I suggest you arrange to have it checked out by and AWS mobile technician.
I think you're right. I'm quite confident I could replace a thermocoupler or clean up a burner, but it would be reassuring to have it fully serviced by a pro.
 
Jul 18, 2017
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If you hob ligts I would nto be very concerned at the moment. After all thsi time more than likely you have air in the system and it will take a bit to rid the air in the system. We had this issue yesterday.
 
Nov 12, 2021
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If you hob ligts I would nto be very concerned at the moment. After all thsi time more than likely you have air in the system and it will take a bit to rid the air in the system. We had this issue yesterday.
The Thetford fridge in my caravan rarely works on gas on first attempt. It often takes three or four restarts before it settles down. I'm used to it now but I used to worry that it was faulty.
As per Buckman's reply, air in the system has to be purged completely before the pilot light will stay lit. The system fails safe very quickly to prevent a build up of unburnt gas and the risk of explosion.
I always get the gas hob lit first and then persevere with the fridge.
Of course on the other hand your fridge may indeed have a fault.
I hope it's an easy solution.
 
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My thetford has a manufacturer label with barcode and serial number on the inside of the door identifying it as model N112, and if you google 'Thetford N112' there are a number of outlets supplying spares, also a number of 'exploded' spares and installation diagrams if that helps.
 
Mar 14, 2005
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Your trouble certainly seems to be thermocouple related. As others have said, make sure the air is purged from the pipework first. Light the hob or oven to help speed up the process. When you've done that, if it still doesn't stay alight, make sure the thermocouple bulb is close enough to the pilot flame to stay hot. If that's ok, test the thermocouple with a volt meter. Heat up the bulb with a lighter or candle flame, then take a reading from the core of the thermocouple - you'll need to undo it from the gas valve. I've had readings of 17mV before - and yet the thermocouple hasn't operated as it should. You need a reading of around 25mV.
If you need to change the thermocouple, there's no need to pay silly prices. Buy a universal thermocouple from the likes of ebay - it'll come with a variety of unions to match your gas valve. Just make sure the one you buy is long enough. Too long, and you can wind a neat coil. Too short, and you're stumped.
 
Jun 6, 2006
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It could also be down to an Earth fault, from switch, sometimes excising the switch can fix this
 
Mar 14, 2005
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The OP has reported he can both hear the gas flow and the flame ignite, so it seems unlikely to be air in the pipes.

So there is some reason why the FFD in the gas valve is not holding open.

  • It could be the thermocouple is not firmly screwed into the gas valve causing a poor electrical connection.
  • It could be something is preventing the stem of the valve its full push travel to open the FFD enough for the thermocouple to hold it. (Something fowling the gas control knob.)
  • It could be the thermocouple is is not producing its hold current when hot. (Could be its tip is not properly immersed in the flame, or it could be the flame is too small, or its not burning correctly and its missing the the tip of the thermocouple). (Does the exhaust smell of, or is it producing soot?)
  • It could be the thermocouple is damaged or worn out and it's just not working.
  • It could be the FFD coil in the valve is not working (it is not recommended to try and open gas valves replacement is the prefered option for a number of safety reasons)
Unless you have access to all the necessary equipment to complete a gas repair and to test it in accordance with the standards, you should refer the installation, service or repair and removal of gas appliances to a trained professional.
 
Jun 20, 2005
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We don’t know what make and model fridge you have. However if it is a Dometic this video will give you some idea of problems. However be warned messing with gas appliances with no knowledge could be fatal. If the problem isn’t a straight forward issue best get the experts in.
View: https://youtu.be/equtZo5EQG8
 
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The fridge in the video is a fully automatic one, and whilst the OP does not tell us the make or model, his description of what he's doing tells me he has a manual ignitor fridge, and the way the gas is controlled and the flame is detected is entirely differnt to the fridge in the video.

There are other video's that cover manual fridges, and there are a host of unsafe if not illegal practices being demonstrated, which I why I won't recommend any of them.

Its pertinent to point out the legal situation. The Gas Safety (installation and Use) Regulations (GSIUR) only allow gas work to be carried out by a fully qualified competent person. However the GSIUR recognise specifically touring caravans and self propelled motor caravans as a special case, and they allow only the owner of said trailer or vehicle to undertake work on the gas system and appliance's, provided the said vehicle is not used by anyone else other than the owner.

However whilst this is a specific exemption for needing to be registering as a gas fitter, it does not absolve the owner from needing to follow all the correct safe working practices and for the health and safety of others who might use the touring caravan or motorhome.

In practice no amature DIYer will have the necessary knowledge or access to the required test equipment to complete gasworks to the required standards, so apart from normal cleaning maintenance as defined in the owners handbook, installing repairing or removing a gas appliance should only be carried out by a fully certified fitter.
 
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Feb 13, 2022
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I’m a bit of a maverick generally, but besides any safety issues, it makes more sense to have a professional diagnose and fix. Perhaps I will do some basic checks though like burner cleanliness and thermocouple position. Other than that, I could end up spending more through DIY trial and error. Just hope I can get it sorted by the end of the month as I have a trip coming up at CL site with no ehu. If I can’t then I’ll have to cancel and go somewhere else.
 
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Nov 16, 2015
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The Thetford fridge in my caravan rarely works on gas on first attempt. It often takes three or four restarts before it settles down. I'm used to it now but I used to worry that it was faulty.
As per Buckman's reply, air in the system has to be purged completely before the pilot light will stay lit. The system fails safe very quickly to prevent a build up of unburnt gas and the risk of explosion.
I always get the gas hob lit first and then persevere with the fridge.
Of course on the other hand your fridge may indeed have a fault.
I hope it's an easy solution.
My fridge is the same, every time out, the fridge needs a few try to ignite before succesfull ignition. I had a new circuit board fitted a couple of years ago. But still take two or three attempts.
 
Feb 13, 2022
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Interesting…. I’m back at the storage yard having a cup of tea and decided to give the fridge another go. Held down button for a long time after igniting then released very gently…. It’s kept going. Leaving it on whilst I sit here drinking my tea and reflecting on my trip. So not sure what it was, air or dirt? All down to technique? I’ll get into the habit of firing it up regularly when I visit the van to burn away any muck which might have got round the burner.
 
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Jul 18, 2017
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Interesting…. I’m back at the storage yard having a cup of tea and decided to give the fridge another go. Held down button for a long time after igniting then released very gently…. It’s kept going. Leaving it on whilst I sit here drinking my tea and reflecting on my trip. So not sure what it was, air or dirt? All down to technique? I’ll get into the habit of firing it up regularly when I visit the van to burn away any muck which might have got round the burner.
More than likely air which makes you wonder how well did the dealer check the caravan before handing it over?
 
Jun 20, 2005
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My fridge is now 15 years old. The gas takes a while to flow through. We then have the ignition delay, then we we need to wait for the thermocouple to heat up. All in all at least 30 seconds holding the button in.
 
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Mar 14, 2005
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It's good you have found a solution.

Air in the pipe can arise when the gas bottle is changed. It is therefore not a reliable indicator of dealers failure to complete a service, or any other work.
 
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It's good you have found a solution.

Air in the pipe can arise when the gas bottle is changed. It is therefore not a reliable indicator of dealers failure to complete a service, or any other work.
I think you are correct there Prof. Every time out my first thing to do is light the hobs then the fridge, and finally after filling the water heater with water light that. Works for me now.
 
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Nov 11, 2009
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I think you are correct there Prof. Every time out my first thing to do is light the hobs then the fridge, and finally after filling the water heater with water light that. Works for me now.
Same here as tge van was on the drive being made ready all gas appliance except water heater were operated, and the fridge was last to be lit. We rarely used it on gas when on site but prior to departure it was given around 10-15 minutes run time.
 
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I think you are correct there Prof. Every time out my first thing to do is light the hobs then the fridge, and finally after filling the water heater with water light that. Works for me now.
You raise a very important point Hutch.

Most reports of failed gas equipment tend to come from people who rarely use them.
Even an annual service does not “ service” but merely tests the function of the gas stuff. If anything is untoward it should be listed as a fault requiring further investigation.
My Thetford Spinflo grill has been a source of the same problem every two or three years. The gas pipe internally rusts which in turn blocks the jet causing failure. Even a new pipe and jet hasn’t resulted in a long term solution. Just poor materials I suspect. But using it and all the other gas equipment as you do seems to keep things clear and maybe stop insects and corrosion blocking things.
 
Mar 14, 2005
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My Thetford Spinflo grill has been a source of the same problem every two or three years. The gas pipe internally rusts which in turn blocks the jet causing failure. Even a new pipe and jet hasn’t resulted in a long term solution. Just poor materials I suspect. But using it and all the other gas equipment as you do seems to keep things clear and maybe stop insects and corrosion blocking things.
Unless you are in the industry of designing and manufacturing gas appliances you may not appreciate the limits and restrictions on the materials you are allowed to use in certain circumstances. For example where an LPG gas carrying pipe passes through a sheet of steel and the working temperature or that sheet can exceed 100C you cannot use copper or other soft metal pipes. Most manufacturers use a treated pipe like a bundy . Bundy is great as it resists corrosion until either ists internal or external surface is scratched or damaged which exposes the steel substrate material which of course can corrode.

The other thing that can damage this type of pipe are sharp bends which can crack the surface finish.

Some manufacturers try to reduce this problem by using coated bundy, which helps but is not a perfect solution.

Whilst the materials used may seem poor, there are regulations that force some decisions about what to use.

This is one of the main reasons why its important for gas appliance's to be periodically checked for safety. A classic example of this was the the Carver/Truma SB1800 model of heater where the heaters gas supply and burner feed pipes should be checked annually and changed when bended sections begin to corrode.
 
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How long it takes to purge any air in a section of pipe work depends on the volume of the pipework and the size of the ignition burner the pipe supplies. Fridges tend to have the smallest burners compared to other caravan appliances, and consequently would take the longest to purge a given length of pipe.

To purge a system its best to purge and ignite all the larger appliances which will remove air from the bulk of the pipe work, Once an appliance has lit and produces a clean regular flame it can be turned off. The last appliance to try should be the smallest gas rate (usually the fridge) , and despite the rest of teh system having been purged, the fridge may take take about 60 seconds of purging per meter of pipe work from the isolator valve before it ignites.
 
Jun 20, 2005
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I should also add Prof the four hob burners after their first journey after resting for three months leave a little pile of rust behind. It means removing the top of the burner, vacuum cleaning the orifice and hob. Not great quality imo but as you say it must be “compliant”.
 
Feb 13, 2022
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Tried the fridge again today, alas it won't stay lit again. I see that the thermocouplers are inexpensive but it's completely unclear which model my fridge is. At the back of it, one of the labels reads N97 followed by a serial number. Yet I'm looking at a manual for a similar van to mine and it lists a two Thetford fridges. The one which looks like mine is the N80, eg. mine is completely analogue and manual. When I look up the N97 all I see is digital ones. So how do I reliably find out what model my fridge is. Will the existing thermocoupler have a part number on it?
 

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