Thretford n112

[Davep]

Hi all the fridge in my van is playing up. It used to work fine on all settings but has gradually got worse on gas. From time to time I would notice the the light was blinking on the Thetford sign. Tuning it off and back on would sort it but not now. I have removed the fridge expecting it to be the thermocouple but I can’t see one on the back of the fridge. When you turn on the fridge you can here the ticking

 

[ProfJohnL]

The symptom you describe suggests the gas is not burning correctly, or the gas supply is restricted.

Unless you are competent in gas fitting , safety and are trained to work on this fridge I strongly reccomend you use the services of a qualified LPG gas fitter to resolve problem and to ensure it fridge is install correctly and safely.

 

[Dustydog]

You describe the classic symptom of a blocked gas jet or even the flue.
During winter storage spiders and other critters make nests causing issues. The flue and jet assembly are easily removed and cleaned. DO NOT try and poke anything through the jet hole. Washing and blowing through is sufficient.

You didn't need to remove the fridge to do this!Access via the exterior vents.

Not sure how you reached your initial diagnosis??

I can only echo the Prof's advice. Incorrect reassembly may lead to the silent killer CO!

Best get a qualified AWS engineer to sort it.

 

[IanB1485]

The thetford gas nozzles tend to close up and the flame becomes higher and the flame detect detect electrode can't see it . The other problem is that the regulator output pressure may be fluctuating causing the flame to jump about. As the others have said it needs checking out by a competent gas engineer, even putting it back in can leave it in a dangerous condition , allowing CO2 and CO into the habitation area.

 

[Martin_E]

It can also be the pcb

 

[birdman101]

If it is sparking but not lighting,most probably a blockage problem. On of my neighbours has the same problem a few years back on his first trip of the year, after standing unused over winter. I took the fridge out so I could give it a thorough check,and found inside the burner a massive spiders nest where it had made its home over winter. Cleaned all out, made sure the gas jet was not blocked and then all worked as it should.

 

[IanB1485]

As Martin -E said if the ignitor is active its not sensing the flame so could be the pcb ( and then after a set time it will give up and declare a fault) whether the flame is present or not has not been observed by the OP ( Or if it has then he has not reported it) the PCB may be faulty in that the flame detection circuit which is connected to the spark circuit is faulty . The high voltage of the spark can damage the flame rectification circuit. I have changed several Thetford and dometic control pcbs with this problem also changed several faulty jets/burners. Once the blocked/ damaged burner/jet assembly has been inspected and cleaned to eliminate that, then, if the fault persists its the pcb , Apuljack and A & R do offer an inspection /repair service , a bit pricey, but cheaper than a new control 'brick'

 

[Davep]

I have sorted it. The thermocouple/ igniter was faulty. New one in place spade connector on and fired straight up. It’s the newer n112 So the thermocouple and igniter is one unit not separate

 

[Hutch]

Well done DaveP, good to hear someone sorting out the problems, that's what PC should be about.
Not taken it to a tech, and pay over the odds.

 

[IanB1485]

Well done, glad to know you have sorted it.
Just one point to note:- its not a thermocouple , which consists of two dissimilar metals usually a type S ,which is Platinum/Rhodium alloy and pure platinum welded together at the 'hot' end. A thermocouple connects directly into the gas valve and holds it open by generating a small electrical current/voltage when hot to a small solenoid coil built into the gas valve. The ignitor electrode is a single rod of tungsten in a ceramic holder (don't ever ever try and bend one ) and when a flame is present this will rectify an A.C current to a D.C one ( thermionic emission like in those old valves) which effectively shorts out the high voltage drive circuit used to create the spark and this 'loading' of the drive circuit is monitored and whilst it is 'loaded' the circuit knows the flame is present and the electronics then keeps the gas valve open. The annoying thing is that manufacturers usually embed this part of the control circuitry in resin making it really difficult and uneconomical to repair the circuit which can just be simple component failure.

 

[Hutch]

Well done, glad to know you have sorted it.
Just one point to note:- its not a thermocouple , which consists of two dissimilar metals usually a type S ,which is Platinum/Rhodium alloy and pure platinum welded together at the 'hot' end. A thermocouple connects directly into the gas valve and holds it open by generating a small electrical current/voltage when hot to a small solenoid coil built into the gas valve. The ignitor electrode is a single rod of tungsten in a ceramic holder (don't ever ever try and bend one ) and when a flame is present this will rectify an A.C current to a D.C one ( thermionic emission like in those old valves) which effectively shorts out the high voltage drive circuit used to create the spark and this 'loading' of the drive circuit is monitored and whilst it is 'loaded' the circuit knows the flame is present and the electronics then keeps the gas valve open. The annoying thing is that manufacturers usually embed this part of the control circuitry in resin making it really difficult and uneconomical to repair the circuit which can just be simple component failure.

I love the reality of a basic explanation of what goes on, being a retired Aviation Engineer.