tcarragher80 Posted August 20, 2020 Share Posted August 20, 2020 i have thetford Cll.....N100EL L.......would not stay on on gas unless you held temp/gas switch in......recomended gas fitter changed thermocoupler...... no better ....said need gas switch...... gas switch fitted.......no better.....suggested he leaves it alone....now it will very rarely light and stay on but red line in gauge goes right to the top.....but will not light again for a long time or not atall.......strange thing is if connect mains it will light up right away .red line at top.. also switch engine on again fires up right away....any help...repair shops fully booked..... Link to comment Share on other sites More sharing options...
Keithl Posted August 20, 2020 Share Posted August 20, 2020 What is the voltage of your leisure battery when no load or charger is turned on? Keith. Link to comment Share on other sites More sharing options...
weldted Posted August 20, 2020 Share Posted August 20, 2020 Check the earth from the 12 volt side, see if it works on hook up but 240 volt off, may be using the earth feed to link it all together. The earth for the gas is separate to the earth when engine is running. Link to comment Share on other sites More sharing options...
tcarragher80 Posted August 20, 2020 Author Share Posted August 20, 2020 will check to morrow .van is 2005 hymer classic 664. panel above door shows both lesiure and engine batt fully charged....do you mean connect mains lead but turn off 240 volt at cut out in van.so i am using earth conn from home... Link to comment Share on other sites More sharing options...
Keithl Posted August 20, 2020 Share Posted August 20, 2020 Unplug the mains lead completely. Ted has (incorrectly) called a 12 volt negative connection a ground, confusing it with a mains earth connection. Keith. Link to comment Share on other sites More sharing options...
Paul- Posted August 21, 2020 Share Posted August 21, 2020 Is this gas fitter one thats on the Thetford list of recommended service agents? Usually the problem that you describe is due to low gas pressure and the usual problem is debris in the burner assembly, a service by an Thetford approved gasman/lady would be my first port of call and most make home calls. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 21, 2020 Share Posted August 21, 2020 I agree. Even if thee is an electrical issue, if the Thetford is originsl (hence 15 years old) and its gas side hasn’t been recently maintained/cleaned, that definitely won’t help. This 2002 manual probably applies https://www.manualslib.com/manual/717570/Thetford-N80.html#manual but I can’t see it helping much with the fault’s diagnosis. (I’m not sure what the “red line in gauge” relates to...) Link to comment Share on other sites More sharing options...
BruceM Posted August 21, 2020 Share Posted August 21, 2020 From the description of the fault it absolutely sounds like it is related to the electrics rather than strictly to the gas supply. I assume that when off EHU and with the engine not running that when attempting to light the fridge you can hear the continuous clicking sound from the ignition mechanism? My guess is that it’s not the thermocouple that was at fault but the flame sensor. The thermocouple creates a small electrical current by warming up in the flame and consequently energises an electro magnet that keeps the gas switch open. When the flame is extinguished the thermo couple cools and the electromagnet releases the gas switch. However it is slow to operate, ie takes a while to warm up and a while to cool down. The flame sensor is designed to immediately sense when the gas flame is extinguished, eg blown out by the wind, and immediately fire up the ignition mechanism again. It works by measuring electron flow through the area of air that the gas flame is situated. This is accomplished by a probe that sits close to the flame and measurers electron flow to –ve. I suspect that the electrode needs cleaning (been there done that). The higher voltage when on EHU/running the engine probably overcomes the resistance created by the dirt layer. Gentle cleaning with a bit of emery paper and contact cleaner or even WD40 may make a big difference. The alternative is that the leisure battery is shot and running at low voltage although I think that you’ve indicated that this is unlikely to be the case. Link to comment Share on other sites More sharing options...
weldted Posted August 21, 2020 Share Posted August 21, 2020 There should be a twelve volt negative terminal attached to the fridge to provide the return to complete the circuit on the 12 volt control side. Which I would describe as the ground in relation to the low volt supply. The reason for leaving the 240 volt hook up connected but not turned on is to ensure there is not a wiring fault as it works fine when on 240. Link to comment Share on other sites More sharing options...
tcarragher80 Posted August 21, 2020 Author Share Posted August 21, 2020 not clued up on electrics but as i said struggles to fire up ,then when it does struggles more to relight..turn on engine it fires up same when 240 connected...Bruce reply seems the most logical..... is flame sencore the little red hot thing behind gas flame ? and how do i clean it ..in situ ?...neeed to rmove ? disconnected liesure batt is fine... fridge was serviced 3 years ago with new gas jet fitted. when lit flame is good and strong blue.....red line is on gauge whitch shows fridge is on gas.. moves slowly up to top green half. normaly sits in midle or there abouts now sits at very top could be nothing it has sat just slightly over centre mark..before...As all motorhome sevice centres been closed bookings very hard to get..booking.....a while back got two thetford engineers for my area they replied they had retired and had long told thetford .nice guys though they answered ......sorry for delay ...shingles wont go away..........p.s got engineers from thetford website...... Link to comment Share on other sites More sharing options...
BruceM Posted August 21, 2020 Share Posted August 21, 2020 I had to work blind on my sensor because my lower fridge vent is on the side of my van. So I can’t be certain but I think that the ignition probe (the probe that produces the spark) doubles as the flame sensor probe. Cleaning can be done in situ. So if it were me, I’d ; Remove the external lower fridge vent to gain access to the burner assembly. Remove the burner assembly metal cover (a couple of screws I think). Wipe any debris/soot from around the burner – maybe with the help of some contact cleaner or WD40. Lay a bit of kitchen towel over the burner to avoid anything dropping into the burner jet. Clean both the ignition probe and the thermocouple probe (I think that they’d be the only two probes there) with emery paper and contact cleaner or WD40. Test it. Reassemble. Test it again. Note, both contact cleaner and WD40 are inflammable so if you douse things you’ll end up with a significant burn when you light up so I suggest that you avoid overspill by soaking up excess by laying down kitchen towel and also by applying the cleaning solution direct to the emery paper/cloth rather than just squirting it onto the probes. If in doubt keep a fire extinguisher or cup of water handy. I'd only add that if it was a Thetford engineer you originally used I'd have expected them to clean the burner assembly and flue first before replacing parts so maybe all this has been done already? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 22, 2020 Share Posted August 22, 2020 The Thetford manual for N100-model fridges indicates that the control-panel of some variants carried a ‘flame meter’ that confirms when the gas flame is lit The meter part is shown on the 1st image below and the manual refers to it within the operating-on-gas instructions as follows ...Release the thermostat when the indicator of the flame meter enters the green area. If it does not enter the green area, repeat the previous step. The fridge’s flame-sensing device is referred to by Thetford (and by advertisers) as a “thermocouple” (2nd image below). The burner unit has no secondary flame-related device. As the engineer who worked on tcarragher80’s motorhome replaced the ‘thermocouple’ (as Bruce has said) it’s to be hoped that the burner unit was cleaned as part of the exercise. It’s perhaps worth saying that, if one is accustomed to Dometic fridges, Thetford models are a bit different. For example, this advert shows a N100’s burner assembly. https://shop.caravanclub.co.uk/product/1020076/thetford-n100-fridge-burner-assembly In this 2017 MHFun forum thread https://www.motorhomefun.co.uk/forum/threads/thetford-fridge-not-working-on-gas.164873/ Dave Newell said Thetford fridges don't use a thermocouple, they use flame rectification to detect combustion. Once the flame is lit the ionized has in the flame conduct to earth from the electrode. The reason yours is still sparking once lit is that the flame failure circuit has failed. This might be due to a dirty electrode or the burner itself may be partially obstructed causing the flame to not hit the electrode, if none of the above them it's likely to be the main pcb which is about £150 or so. Link to comment Share on other sites More sharing options...
BruceM Posted August 22, 2020 Share Posted August 22, 2020 I suspect that Derek is correct and the burner components are different to my fridge although the operating method will be similar. So I’ve pulled out a Thetford burner diagram and ledged which might assist. It’s for a later model however it’s possible that the design has not changed much. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 22, 2020 Share Posted August 22, 2020 This link http://www.swift-owners-club.com/support/oem-handbooks/thetford/fridge-spares-2002-5.pdf suggests (Pages 26 & 27) that a N100's burner unit will have been much the same. Link to comment Share on other sites More sharing options...
tcarragher80 Posted August 25, 2020 Author Share Posted August 25, 2020 thanks all for your help .did all that bruce sugested, everything was there as he described .cleaned all with electrical connector spray .did start up first time but but when turned off took a long time to start up again. when working correctly it fired up quickly. the dreaded slight health problems keeping me away from working on van , will get in touch when all working again......again thanks to all........p.s electrical contact spray always carried in wifes mobility scooter ....when it starts slowing down suddenly ....found speed controle similar to guitar and amp volume controle a good spray whike turning it with power off works .....usually caused by damp..cheers Link to comment Share on other sites More sharing options...
snail Posted August 25, 2020 Share Posted August 25, 2020 Hi, been following this thread, we have identical van as you from new, over the years we have had some faults the fridge had a new gas valve, thermocouple and stat, I clean the flue every year, BUT the main thing that improved the fridge was changing the bulk head regulator in the gas locker even though every other appliance worked fine, we run on gas low bottles and fill from lpg pumps in garages, the regulator was 12 years old and replaced with another gaslow one Link to comment Share on other sites More sharing options...
tcarragher80 Posted September 5, 2020 Author Share Posted September 5, 2020 fridge working o.k. .....after engineer left turned fridge off..could not relight......managed ti light it left on.....3 hours later is off....the lower space whitch i cleaned was dirty.. and the red line moved to very top of green zone never before always half way.. so i assumed was flame to high..when we had service after buying van from new top vent panel had melted .no reple from hymer... I cleaned lower panel and did what bruce said cleaned all withcontact cleaner ....still same.....it was booked in to Stewart Longtons last thursday.... engineer says nothing wrong red line should be at top when flame is correct and does take while to relight.....so left it on he said go for walk couple of hours .Chorley is a nice place.. came back still on......engineers boss said we can,t do anything to it so no charge....nice people ..at Stewart Longtons Chorley.......... many thanks to all......... Link to comment Share on other sites More sharing options...
BruceM Posted September 6, 2020 Share Posted September 6, 2020 Getting (my own mind) back on diagnostic track, As I see it the current status is: 1/ The burner assembly has been cleaned 2/ The thermocouple and gas switch have been replaced 3/ The fridge lights just fine if the engine is running or whilst on EHU 4/ The fridge will not light when the engine is not running or off EHU I think this still seems to point to an electrical issue. The question in my mind is whether a spark is being generated to light the gas when not on EHU etc. Would it be possible to visually check for a spark whilst off EHU and engine turned off and then do the same with either the engine running or on EHU? If we could establish whether an ignition spark is being generated that would at least narrow down the potential issues. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted September 6, 2020 Share Posted September 6, 2020 The final posting (and the saga that preceded it) of this Wildcamping forum thread may be of interest - or create despair... https://wildcamping.co.uk/threads/thetford-n100e-fridge-problems.36539/ Link to comment Share on other sites More sharing options...
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