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Fridge Gas Ignition issue.

3K views 34 replies 6 participants last post by  Pudsey_Bear 
#1 ·
Hi,
I am not new to 3 way fridge on gas problems but this one different for me.
Brief introduction, RM6401L (old!).
Burner assembly changed 2 years ago and chimney swept! All well.
Recently would not light on gas, burner removed and blockage of jet remove with compressed air.
Now lights on gas and stays lit after release of knob.
So far so good.
However the ignition continues without ceasing. Now I believe the thermocouple current holds the gas valve open, which it does, BUT why does the ignition continue? The thermocouple is obviously giving an output to the gas valve.

Does anyone know how the igniter is designed to know that the burner is lit and therefore cease?
Attached is a diagram that I worked on the last time I was wrestling with the fridge. At that time I commented that I could not see how the ignition ceased.
Any advice gratefully received.
 

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#3 ·
I cannot answer your question but:-

I did have this issue in our last Bessie "However the ignition continues without ceasing" I'm not sure of the cause, but after the fridge was lit I took the outside vent cover off and removed the black wire from the ignitor, this stopped it from clicking, and I had to put it back and repeat each time I went from 12v, not a proper fix but it worked while we were away, I never got around to fixing it as I sold the van.
 
#4 ·
Thanks for the response,

I'll ease out the fridge and take another look at the gas valve connections. I'll also change the thermocouple for an old one that I have.

The fridge is 19 years old so not a bad innings but the cost of a new one is substantial!
Is it likely that a new model is available to fit exactly the space occupied at present?
 
#5 ·
Google fridges at O,Brians
 
#7 ·
#8 ·
A renewed look at the gas control valve.
There are 4 connections.
1. Gas in
2. Gas out.
3. Thermocouple.
4. 2 terminals, connected to energy type selector switch.


These terminals at present (fridge out, and disconnected) are internally shorted together, I assume because the gas valve is closed.
The selector switch provides an external short to these terminals except when gas is selected.


There is an attachment (thermostat) to the gas valve assembly which I think is connected to the temperature control which has no function when the fridge is on gas.


In other words, I fail to see how the ignited knows when to stop.
 
#10 ·
A renewed look at the gas control valve.
There are 4 connections.
1. Gas in
2. Gas out.
3. Thermocouple.
4. 2 terminals, connected to energy type selector switch.

These terminals at present (fridge out, and disconnected) are internally shorted together, I assume because the gas valve is closed.
The selector switch provides an external short to these terminals except when gas is selected.

There is an attachment (thermostat) to the gas valve assembly which I think is connected to the temperature control which has no function when the fridge is on gas.

In other words, I fail to see how the ignited knows when to stop.
I would presume that normally the thermocouple is at room temperature on firing up, once the pilot lights it heats up and disconnects the ignition sequence. I am not a gas engineer but would think it is a thermocouple failure - not generating the required voltage.
 
#11 ·
Thanks for the additional replies.


Sadly by physical examination of the wiring and components AND inspection of the wiring diagram (previously posted), I cannot see any connection to the ignition generator from anything else. Previously, when functioning normally, the spark would cease when the burner lit, on release of the push button if the flame failed the ignition would restart. Logic would suggest that somehow the igniter is acting on thermocouple output. At present only gas valve is reacting to the thermocouple by being held in after button release.

Under normal conditions the ignition process would occur when switched to gas and the burner unlit; even with gas valve pushed in it would continue until a flame was established. One could imagine an optical flame detector controlling the process, but that does not exist.



A thermocouple change is on the cards. Owing to cost of a new fridge, approx £1100! , plus installation!! I'll spend some effort in trying to resolve it. In addition a new fridge is scare at the moment for reasons we all know why.
 
#15 · (Edited)
Domage…. Or Merde but that’s less acceptable…

My only other suggestion would be to “ask an expert” as clearly there is something that we do not know.

I know that Dometic/Thetford have servicing agents throughout Europe, our local one is a wizard and is happy to talk through problems with people. The only problem with giving you his number is that he speaks no English so unless your French is above most bilingual people including my daughter who happily gets accused of “being French, not English “ even though she is actually British and German but also is fluent in Italian as well. She struggles with the technical topics though (as do we).

Have you an agent near you that you could contact ?

Sorry, I know that’s an admission of failure, but even if you use such an agent it will still be much cheaper than a replacement.

Just a thought though before you take that route…..

The ignition is started by pushing the knob in to override the gas block.

It’s not by any chance sticking in is it ? I know it’s a pull off knob but if pushed in TOO hard it is possible to wedge it in so it would continue to spark…..

That would be the cheapest problem of any, try pulling it straight off and push it back more gently. You can initiate the sparking procedure by gripping the shaft with a pair of mole grips and pushing it in, I have done that in the past.
 
#16 ·
Many thanks for all response to this problem.


Yesterday I managed to get the name of a local Domeic engineer and I 'll give him a ring shortly.


I am also considering putting a swich in an adjacent cupboard that interupts the -12v to the igniter generator. One needs to know that the flame is lit before using it, that means a visual sighting or perhap feeling the heat from the vent. This idea came from Pudsey_Bear. Looking at the diagram, the removal of 12v to the fridge after ignition would not cause a promlem, so pulling a fuse would stop the sparking.



As indicated before the spark generator is started by the permanent application of 12v directly from gas selector switch.
I'm at a loss to know the mechanism on stopping the spark once lit. I just wonder if the generator (via the electrode) has a method of sensing the impedance of the air gap in the burner. Can it detect cold gas versus hot gases? Seem very unlikely.


I'll report on the final outcome but it maybe a while.
 
#18 ·
#21 ·
I KNOW the answer to that is yes, it happened to us.

The knob fits onto a shaft with a flat, that goes through a panel and the mechanism behind it CAN stick, hence my suggestion to grip the shaft with a Mole wrench and make sure it has come out. Sounds simple, but it’s often the simplest things that are overlooked.

In our case it only needed freeing up and has worked perfectly ever since, I am not sure exactly what lays behind the panel I do not know, but presumably that mechanism can seize up, or the spring get blocked from full travel.

Worth looking at anyway.
 
#22 ·
Thanks Penquin, I'll look into that.

I should be cutting the lawn but I can't let this go!.
I came across this subject on another caravan website, "Spark Rectification".
See https://www.igniters.co.uk/principle.htm
I have a feeling that this will be the issue.

Also confirmed, with a lit burner, switching of the 12v has no effect, turning selector switch away from gas, as expected cause gas cut off.

Bit depressing, when looking at fridge spares, "No Longer Available" applies to lots of items.
 
#23 ·
#25 ·
You have my sympathy, mine was pretty much condemned yesterday.
 
#26 ·
Hallelujah, the end of the saga.
Success it works! You never stop learning, all down to spark rectification. Before ordering a new igniter generator I did a few checks.
Supplementary earth appied to burner, 3 pin socket on igniter reseated several times, all to no effect.
Re-inserted, several times, the electrode wire into the igniter, Bingo ignition, light operates as it should.
Conclusion. Poor igniter lead connection to spark generator.



Many thanks to all.
 
#27 ·
Thanks for letting us all know, I am really pleased that you have managed to sort it, now if you can just help Pudsey who’s fridge seems to have died totally. It sounds like you solve problems using research and trial as well as error, but logic has prevailed.

I am sure Pudsey would welcome any input you can offer. 🙂
 
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