# Thetford N145 gas problem.



## hampsterracing (Jun 2, 2011)

My fridge lights ok but will not stay alight.

the jet burner and exhaust tube are clear and clean.

it appears not to know the burner is alight.

the sparker and flame probe are combined it sparks and lights fine.

the probe is high in the gas flame and glows.

Any bright ideas

thanks

roger


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## rosalan (Aug 24, 2009)

The question poses several possibilities which I am sure that you will have considered.
1. For some reason you have air in the gas feed: Not very likely as it does initially work.
2. A faulty sensor: Possible solution.
3. A poor alignment of the heat sensor to the main heat source: This is wild thinking on my part, in that the heat sensor works when prompted by the ignition but cannot remain hot enough under normal operation and cuts out.

Solution: Contact a Dometic/Electrolux/Thetford engineer, who may charge an arm and a leg but should solve the problem with a replacement part or know which bit to bend.

Sorry about the last solution, for I like to fix anything that does not work but having been down a similar pathway to yourself and finally resorting to a call-out (at a Motorhome Show), I now appreciate that even if I had fitted the new part I required, I doubt that it would have worked. He cut bits off, bent pieces, cleaned bits, replaced a jet all within his fixed charge. Worked perfectly ever after.

Alan


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## hampsterracing (Jun 2, 2011)

Thanks alan

i was hoping for someone with experience on this type of burner.

i have plenty of gas experience but on large industrial systems.

i am presuming the spark probe and detection are combined as there appear to be no other ones.

i will order a spark probe at some point to try as they are not a bad price.

it is not a supply problem as the burner is perfect until it cuts out as it has not detected the flame.


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## rayc (Jun 3, 2008)

I would be interested in the technicalities of how the spark electrode is also the flame failure device to cut off the gas valve.

There is a fault finding flow chart for Code 9 failure in the attached link.
http://www.swift-owners-club.com/support/oem-handbooks/thetford/troubleshooting-fridges.pdf


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## pippin (Nov 15, 2007)

I had this problem - and still occasionally intermittently do.

The sparks would light the gas.

The sparks continued for a few seconds - which is normal.

The sparks then stop and the electrode is then selected by the pcb to act as a flame sensor.

The pcb then seemed to think that the flame wasn't lit and the sparks would restart.

The flame was still well lit and blue.

After a few more seconds of sparking they would stop and the pcb would look at the sensor to check if the flame was there.

It would then shut down the gas on the basis of flame failure.

I tried a new electrode, which sort of helped but it was still intermittent.

I bent the electrode so that it really glowed hot in the flame.

That reduced the intermittancy but has not sorted the problem totally.

I do find that when it fails and switches off that repeated attempts will eventually get it to work.

Baulking at the probable cost of a gold-plated new pcb - I have learned to live with it.


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## hampsterracing (Jun 2, 2011)

It is a code 9 fault.

i have stripped and cleaned and re-setup the burner and probe.

still no joy :-(

it times out after 30 seconds

i have spoken to cak tanks and thetford both suggest it is a pcb fault.

i am struggling to bring my self to pay the £120 + for a new board on a maybe !

although i did have a fault where it would not work on 12v whilst driving and reset it by pulling the fuse on the permenant live fixed this may also point to a board fault.

*** pippin***

i have tried various heights/positions for the probe and it still wont stay alight :-(


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## rayc (Jun 3, 2008)

> hampsterracing said:
> 
> 
> > It is a code 9 fault.
> ...


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## hampsterracing (Jun 2, 2011)

rayc said:


> > have you checked the three fuses on the PCB? Have a good look at the rear of the PCB with a lamp and magnifying glass. Flex it and look for anything that could be a dry joint and re-solder anything suspicious. The circuits on these boards are fairly simple and the components cheap and their price no where near reflects their cost to manufacture.
> 
> 
> I have checked all 3 fuses all fine.
> ...


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## rayc (Jun 3, 2008)

Can anyone explain how the spark electrode becomes a flame failure device? I can see that it connects to the spark generator on the PCB and I am just trying to understand the technicalities.


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## hampsterracing (Jun 2, 2011)

That is what i would like to know as well !!

If i remember some old gas stuff it may become a flame rectification probe and pick up some dc through the earth (i checked/cleaned all of the earths just in case)


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## suedew (May 10, 2005)

Don't know if this helps but had a this fault on our fridge, might be a different model, manual ignition, problem was a loose spade connector, unfortunately fridge had to come out as they are handilly sited on top of the fridge :roll: 
unfortunately happened again this time out am fairly happy playing with most things, but not when i have to disconnect and reconnect gas pipes. works fine on mains and when engine is running.

sue


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## rayc (Jun 3, 2008)

> suedew said:
> 
> 
> > manual ignition, problem was a loose spade connector,
> ...


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## hampsterracing (Jun 2, 2011)

I have already removed/checked cleaned and refitted the connection.

keep them coming though 

thanks

Roger


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## pippin (Nov 15, 2007)

That does not apply in this case, only when there are separate spark and flame detection devices.

On these modern fridges the spark is not provided by a piezo-electric device (the push-button type).

It is provided by the secondary of a high voltage transformer.

The flame detection is measured by the pcb cctry via the (high resistance) secondary of that same transformer.

Quite how it does that, I'm not sure.

A microprocessor will almost certainly be involved.

Hence the gold-plated price of a new pcb!

Just to be clear - the ignition spark and flame detection are via the same probe and somehow pass through the same transformer.

I will research.


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## hampsterracing (Jun 2, 2011)

hoping to get the boards out for an inspection this afternoon if the weather plays ball !


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## Ian_n_Suzy (Feb 15, 2009)

> hoping to get the boards out for an inspection this afternoon if the weather plays ball !


Hi,

I had the identical issue on my own N145 till recently. I used the wife's nail files to clean up the end of the electrode and where the spark arrests to and also made sure it was in the hottest part of the flame.

As I no doubt you have tried the above, the real reason for my post is to say if you do need the PCB you will be VERY lucky if you can find anywhere with it in stock. I've decided to buy one to carry as a spare "just in case", but as of now have been unable to locate one at a fair price (if at all).

Also make sure you get the correct version as there are 2 for the N145, one for the Auto and one for the Manual (AES/SES I think).

GOOD LUCK


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## Ian_n_Suzy (Feb 15, 2009)

This Thetford Repair Instruction Manual (.PDF) may be of use to yourself and others, certainly worth grabbing for a "rainy day".

Pages 39 onwards detail pictorially the removal of the PCB.

http://ourimages.net84.net/wheel/refrigeration-repair-instructions.pdf


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## hampsterracing (Jun 2, 2011)

Ian_n_Suzy said:


> > Hi,
> >
> > I had the identical issue on my own N145 till recently. I used the wife's nail files to clean up the end of the electrode and where the spark arrests to and also made sure it was in the hottest part of the flame.
> >
> ...


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## hampsterracing (Jun 2, 2011)

Ian_n_Suzy said:


> This Thetford Repair Instruction Manual (.PDF) may be of use to yourself and others, certainly worth grabbing for a "rainy day".
> 
> Pages 39 onwards detail pictorially the removal of the PCB.
> 
> http://ourimages.net84.net/wheel/refrigeration-repair-instructions.pdf


Very usefull

saved for furure reference


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## hampsterracing (Jun 2, 2011)

new board info


Power Board Part Number for Fridge models: N145-N150-N175-N180

634422 SR Power Board Auto Old Part Numbers: 631219, 626970

634423 SR Power Board Manual Old Part Numbers: 631220, 626971


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## hampsterracing (Jun 2, 2011)

The board has been fully inspected and one suspect looking earth joint repaired.

still no go so i will have to order a board today :-(


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## rayc (Jun 3, 2008)

> hampsterracing said:
> 
> 
> > still no go so i will have to order a board today :-(
> ...


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## hampsterracing (Jun 2, 2011)

rayc said:


> > Good luck, hope it solves your problem.
> > Did you replace the spark ignitor/ flame sensing device?
> >
> > The system of having the same device provide ignition and sensing is apparently Direct Spark Ignition (DSI). "The heart of the system is the solid state ignition module that provides both the high voltage spark to ignite the burner, and then the means to monitor the flame. Once the
> ...


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## hampsterracing (Jun 2, 2011)

I cooled the fridge down on 240 as (i am away for a few days now) after i finished testing the gas this morning. And 240 is still working fine. 

After loading the van i changed over to gas again and the @$#&@$ thing worked !

I have been traveling this evening with a few stops so have changed between 12v and gas a few times and i am now parked up in a wildspot for the night and it is behaving perfectly !

The bloody thing knew i had ordered a new powerboard !!

But at least the beers will be cold for the carnival tomorrow night


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## hampsterracing (Jun 2, 2011)

Just got home after three nights away and it has run on gas or 12v the whole time with only one "moment" and that turned out to be the gas bottle was empty  .

seems as if it is ok for now.

i will update in the future if i have any more problems.

Thanks for all the links and suggestions.

Roger


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## hampsterracing (Jun 2, 2011)

i popped away for one night last weekend and the fridge refused to work on any power source :-(

so i bit the bullet and fitted the new power board yesterday.

it now works on all three sources. a full test will have to wait until after christmas .


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