Dometic fridge won't run on gas

[IanB1485]

I disagree with the thermocouple itself being faulty , IMO it's the selector switch.
One trick to try without pulling the fridge out is to , whilst holding the gas valve in and the flame is lit to gently turn the selector switch slightly back away from 'gas' and back to gas , if the indicator twitches slightly or starts to move to the green section , then it's definitely grease on the contacts of the switch contacts.

 

[ProfJohnL]

Yes, thermocouple, I suggested that in #4

John

I would clarify that to say the thermocouple circuit, as often the thermocouple itself is fine, it the electrical contacts, either in the switch that Ian B has written about, or in the valve where the thermocouple's connector is supposed to screw in and seat and make contact.

 

[Kevin M]

With this being a possible fault on a gas appliance, get a real professional to service and repair the fridge before something goes wrong and it all ends up in disaster .

 

[Jcloughie]

I would clarify that to say the thermocouple circuit, as often the thermocouple itself is fine, it the electrical contacts, either in the switch that Ian B has written about, or in the valve where the thermocouple's connector is supposed to screw in and seat and make contact.

Again. Much of that suggested in #4.

I take on board what Ian suggested. But a weakness in the control circuits is indicated. I would always start with the cheapest, so Ian’s switch, then the thermocouple, then the valve.

With this being a possible fault on a gas appliance, get a real professional to service and repair the fridge before something goes wrong and it all ends up in disaster .

The gas system is not touched unless it is the valve that is at fault.

John

 

[IanB1485]

Unfortunately under gas safety ( installation and use) regulations 1998 'work' on a gas appliance includes moving it or dismantling any part of ,so even if you don't touch the gas side it should only be undertaken by a qualified person. To illustrate this point I was , after servicing a caravan including a full gas integrity check and noted on it that one of the gas burners wouldn't stay lit , asked to repair it.On pulling the oven forward to get at the lid switches ( I have stand on which to rest the front of oven) and the side panel to get at the gas valve and thermocouple the inline gasoline union to oven developed a tiny leak as detected by as my gas sniffer and manometer. A person who has not attended an approved gas course, who might be a very competent engineer in other disciplines may not have the equipment to check that after the work is completed the gas system is completely leak free and safe to use. Only 3 weeks ago a Motorhome/campervan in Livingston suffered a gas explosion.After working or repairing the oven you should call out a gas engineer/mobile caravan engineer to just check it out, I call out a friendly gas safe engineer to check my work when having worked on my home condensing boiler.

 

[ProfJohnL]

I call out a friendly gas safe engineer to check my work when having worked on my home condensing boiler.

I think it needs to be made clear that in the instance you have given, you have only worked on your domestic gas installation becasue I presume you have the required gas fitting certification and registration that allows you to do so. Most caravanners will not have the certification and registration to work on domestic gas installations, and in fact would be committing a criminal offence if they were to do so.

I am aware of a case where a householder had built and new utility room and moved his gas boiler and some other gas pipe work by himself. After the move he did contacted a qualified gas fitter to come and certify the works. The fitter attended the site, he found several non conformaties , and he refused to certify the installation. In fact he issued an ID notice, on the whole house installation. The local council were involved, and I understand the housholder was fined with a suspended sentence for breaches of GS(I&U)R under Health and Safety law.

 

[Jcloughie]

Unfortunately under gas safety ( installation and use) regulations 1998 'work' on a gas appliance includes moving it or dismantling any part of ,so even if you don't touch the gas side it should only be undertaken by a qualified person. To illustrate this point I was , after servicing a caravan including a full gas integrity check and noted on it that one of the gas burners wouldn't stay lit , asked to repair it.On pulling the oven forward to get at the lid switches ( I have stand on which to rest the front of oven) and the side panel to get at the gas valve and thermocouple the inline gasoline union to oven developed a tiny leak as detected by as my gas sniffer and manometer. A person who has not attended an approved gas course, who might be a very competent engineer in other disciplines may not have the equipment to check that after the work is completed the gas system is completely leak free and safe to use. Only 3 weeks ago a Motorhome/campervan in Livingston suffered a gas explosion.After working or repairing the oven you should call out a gas engineer/mobile caravan engineer to just check it out, I call out a friendly gas safe engineer to check my work when having worked on my home condensing boiler.

It does not actually say that, you have used a bit of license there.

work” in relation to a gas fitting includes any of the following activities carried out by any person, whether an employee or not, that is to say—

(a)
installing or re-connecting the fitting;
(b)
maintaining, servicing, permanently adjusting, disconnecting, repairing, altering or renewing the fitting or purging it of air or gas;
(c)
where the fitting is not readily movable, changing its position; and
(d)
removing the fitting;
but the expression does not include the connection or disconnection of a bayonet fitting or other self-sealing connector.

You then need to look at the word ‘fitting;’ in the text of the regulations.

gas fittings” means gas pipework, valves (other than emergency controls), regulators and meters, and fittings, apparatus and appliances designed for use by consumers of gas for heating, lighting, cooking or other purposes for which gas can be used (other than the purpose of an industrial process carried out on industrial premises), but it does not mean—

(a)
any part of a service pipe;
(b)
any part of a distribution main or other pipe upstream of the service pipe;
(c)
a gas storage vessel; or
(d)
a gas cylinder or cartridge designed to be disposed of when empty;

Neither the thermocouple or the switch come in this category. Therefore, I stand by my comment in post #29


Alway wise to quote regs verbatim.

However. I fully agree that work should only be undertaken by a competent person. And, where it involves gas fittings as described above. A person with the relevant qualifications for that gas category.


John

 

[otherclive]

It does not actually say that, you have used a bit of license there.

work” in relation to a gas fitting includes any of the following activities carried out by any person, whether an employee or not, that is to say—

(a)
installing or re-connecting the fitting;
(b)
maintaining, servicing, permanently adjusting, disconnecting, repairing, altering or renewing the fitting or purging it of air or gas;
(c)
where the fitting is not readily movable, changing its position; and
(d)
removing the fitting;
but the expression does not include the connection or disconnection of a bayonet fitting or other self-sealing connector.

You then need to look at the word ‘fitting;’ in the text of the regulations.

gas fittings” means gas pipework, valves (other than emergency controls), regulators and meters, and fittings, apparatus and appliances designed for use by consumers of gas for heating, lighting, cooking or other purposes for which gas can be used (other than the purpose of an industrial process carried out on industrial premises), but it does not mean—

(a)
any part of a service pipe;
(b)
any part of a distribution main or other pipe upstream of the service pipe;
(c)
a gas storage vessel; or
(d)
a gas cylinder or cartridge designed to be disposed of when empty;

Neither the thermocouple or the switch come in this category. Therefore, I stand by my comment in post #29


Alway wise to quote regs verbatim.

However. I fully agree that work should only be undertaken by a competent person. And, where it involves gas fittings as described above. A person with the relevant qualifications for that gas category.


John

I think that you have used “fitting” with some degree of licence.

 

[Tel7]

Definitely the selector switch as if the flame lights and the needle does not move it shows the thermocouple circuit is open circuit. ...etc...

Awesome directions, thanks again Ian! Those photos are worth a few thousand pixels, too.
I'll see if I can find those four screws located on the inner side walls covered with white plastic caps, next time I visit the caravan, then give the fridge a pull and see if the gas pipe is long enough to allow it to move toward me enough to get the selector out.
Sorry for the delay in responding.

 

[Jcloughie]

I think that you have used “fitting” with some degree of licence.

Not me, it was a direct quote.

John

 

[trevormonty]

My fridge has faulty selector switch. Burner starts but goes out when I stop pushing gas control. Switching back and fore between 12V, 230V and gas fixed it . I now leave if permanently on gas.
Thought I had to remove fridge to access switch but may give it another look and see if accessible from front.

 

[Dustydog]

My fridge has faulty selector switch. Burner starts but goes out when I stop pushing gas control. Switching back and fore between 12V, 230V and gas fixed it . I now leave if permanently on gas.
Thought I had to remove fridge to access switch but may give it another look and see if accessible from front.

What year make and model is your fridge. As we all know there are numerous different makes and models.
So none of the last 35 posts have helped?

 

[IanB1485]

It will need pulling forward to access the switch and remove the top cover of the switch to access the thermocouple contacts to clean the grease off the contacts , which is stopping the thermocouple current flowing.

 

[Tel7]

Definitely the selector switch ...

Hi Ian,

I visited the caravan a few days ago, and removed the 4 screws which hold the fridge in place, and was able to pull it out a bit. Not far enough to fully remove the cover that covers the fuel selector switch, but enough to lift that cover enough to pull the fuel selector switch out. I didn't have time to short the thermocouple terminals you mentioned, with wire, and test it, but now I have the switch at home.

I've taken it apart, which looks like this, and removed the thermocouple contacts (6a & 6b) which look like this close up.
With a DMM set to ohms, I can't detect any resistance around any of the contacts yet, but could you please confirm the main area I should be testing - is it where I have the screwdriver pointing in that last photo?

I assume that yellowish grease is there for lubricating the part which is contacting (apart from the spring which also contacts). Do I just remove all that grease from the contacting area? If so, what is it meant to be greasing?

In my previous visit I was able to temporarily get some mains power to the caravan, and I tried running the fridge off mains. This worked in 2024 when we tried it, but it now fails. Does this give clues to a different source of the problem? I assume the thermocouple isn't involved with mains power, but the selector switch clearly still is.

Thanks again for your time and expertise.

 

[trevormonty]

If there is grease on terminal probably dielectric grease, helps protect against corrosion and lube mechanism. Worth applying some more sparely at assembly if you have some.
Removing reassembling maybe enough to make dodgy contact work. Give all the contact points a clean with isopropyl alcohol and gentle rub with pencil eraser. Reassemble test a few times by switching between positions..

Before reinstalling, short two wires from fridge going to switch's gas contactor terminals. If switch was problem fridge should run on gas.