RE: Thetford Caprice Mk 3 Stove/Oven combination ..

Jonathan · Senior Member

RE: Thetford Caprice Mk 3 Stove/Oven combination ..

Dougwe · Chief one feather

Do you have "Wit's" Jon biggrin Sorry mate, couldn't resist that, you know what I'm like. Craaaaaaaazzzzzzyyyyyy.

I have the very same stove but all four gas jets, so far so good. I will check mine later cos it's not GN working hours yet but can they come loose in travel and you might not have fitted them back properly confuse Just ask'n mate.

Just thinking on it though, they might even have a screw (oh no) that holds the jets in place and not tight, just another thought.

-- Edited by Dougwe on Thursday 27th of November 2014 07:05:58 AM

Jonathan · Senior Member

.. mornin' Doug ..

stop waking up with your wits about you .. Makes me wonder wits been goin on? .. hehe

.. would you know Doug .. used one of the big burners this morning .. worked just fine ..

bit liked a car indicator .. sometimes it's on .. sometimes it's off !

dorian · Guru

I can't help, but FWIW I found the following documents while searching for an answer.

Parts Lists and Exploded Drawings:
www.campshop.nl/dbdocs/attachment_19.pdf

Service Procedures:
caravanchronicles.files.wordpress.com/2013/03/cooking-appliance-service-procedures.pdf

User and Installation Instructions:
www.rvworldstore.co.nz/media/wysiwyg/Manuals/MK3_CAPRICE___MINIGRILL_ISSUE_1.pdf

Jonathan · Senior Member

Thank you Dorian ..

I do appreciate your support mate ! .. while I have looked at many postings and manuals, I will still definitely peruse these url's ..

Should I find detail that eliminates the problem, I will posyt any findings here ..

cheers !

dorian · Guru

I know essentially nothing about gas appliances, except for the reading that I've done in the last day, so my thoughts on the subject may be way off the mark.

AIUI the stove has a "flame failure device" (FFD) in each burner which shuts off the gas supply to the burner in the event that the flame is extinguished. The way it works is by sensing the temperature of the flame using a thermocouple. The thermocouple voltage (approximately 5mV) drives a safety valve in the tap. As long as this voltage is of sufficient magnitude (greater than 2mV or so), the safety valve remains open.

The way that the burner is lit is by depressing the tap's control knob, thereby opening the valve. As long as the knob is kept depressed, the valve remains open, irrespective of the thermocouple voltage. Once the flame is lit, the knob can be released and the thermocouple voltage then keeps the safety valve open.

ISTM that one could eliminate the safety valve and thermocouple as possible culprits simply by holding down the knob for a minute or so. This keeps the safety valve open irrespective of any problems in the thermocouple system. If the flame remains lit, then this would suggest that there is no problem with the gas flow.

To troubleshoot the thermocouple system, one could try interchanging the FFD solenoids between the good and bad burners, assuming they are identical. The following LG service manual has pictorial guides that show how to do this in a domestic gas oven.

http://www.jordansmanuals.com/Default.aspx?Brand=LG&Product=Ovens&Model=HG6412A

Jonathan · Senior Member

dorian wrote:
.. .. .. If the flame remains lit, then this would suggest that there is no problem with the gas flow .. .. ..

Thanks dorian ..

The flame will always stay lit as long as the button control is held in ..

This tells me then to concentrate around the thermocouples. Whilst in Orange NSW, 2 x thermocouples were replaced by a gas fitter and it seemingly worked well for a short time ..

I will now look further around that zone .. or again, get a qualified fitter to look into it .. My skills in this area lack diversity, so some professionalism might again be the call ..

thanks mate ..will advise when I've progressed further ..

Heading back up to Tamworth shortly, so will follow up then ..

cheers !

dorian · Guru

I was hoping that an experienced gas fitter would chime in and give us the benefit of his knowledge. In the meantime I've been trying to get to grips with the subject using Google.

ISTM that the logical way to troubleshoot this problem would be to compare the voltages at the safety valves of the good and bad burners. That should tell us whether the thermocouple is providing insufficient output, or whether the safety valve is not responding correctly. You would do this while holding down the gas knob to maintain the gas flow.

Unfortunately I've been unable to find this voltage spec in Thetford's documents. However, I've found some conflicting information in other service manuals. For example, an Arlec gass appliance manual talks about thermopiles rather than thermocouples and suggests that these terms are sometimes used interchangeably. In fact a thermocouple is comprised of a single bimetallic junction, whereas a thermopile consists of numerous thermocouple junctions wired in series. The output voltage for a thermocouple is of the order of tens of millivolts while the output voltage for a thermopile appears to be typically around 1V or more. Moreover, Arlec state that their safety valve can be tested with a 1.5V alkaline battery. I've also found datasheets for "millivolt gas valves" which talk about operating voltages of the order of 750mV.

I'm also having a hard time trying to understand how a voltage of 5mV is able to drive a relatively massive electromagnet. Such a voltage wouldn't have the power of a flea's fart and would normally need to be amplified. However, LG's manual does not make reference to any additional electronics, either in the text or in the photos. Therefore I'm wondering whether this voltage operates some kind of trigger mechanism which then enables the gas pressure to amplify the mechanical action in some way.

Jonathan · Senior Member

.. hehe .. lucky I'm immune to a fleas back-pressure ..

Your electrical knowledge is a benefit and appreciated .. I'd like 10% of it ! .. I personally won't start delving into the electronics as I'd be well out of my league.

One never knows where support comes from Dorian, and as I wished to know more about this issue, I put it out on here .. I also thought there may have been others that had personally done a "walk-through" on this problem whereby I might have gained some insight.

That's all good .. not rushing it at all .. and thankful for whatever info is gained ..

.. and FYI as it would happen, over the last 2 days I have been able to use both of the large burners, separately and together. One however, has actually run for over 2 minutes when it simply stopped burning .. I listened for the sound of "flowing" gas but it was not evident .. when this has happened in the past, usually within the first minute, I've never been able to get a re-ignition at all when the burner was still hot .. and this again was the case !

cheers !