Smev oven - will replacing the thermocouple fix this?

[KompetentKrew]

Hello,

My oven, a 25-year-old Smev 300 series, has a peculiarity that it doesn't like to stay lit unless fed WD40 on a regular basis.

Like all modern gas stoves, the knob must be held down so that the flame can be lit, and then for a few further seconds until it is hot.

All the burners on the hob work fine, although it seems like one or two need holding down longer than others.

The oven will work fine for a few days at a time, and then one day the flame will go out as soon as the button is released. It doesn't matter how long it is held down, or seemingly how hot the oven's burner has got - as soon as the button is released the flame goes out. I've tried holding it for 30 or 60 seconds, I reckon, and when lubricated it works within 5.

I was instructed by the PO to remove the knob when this happens and to spray a little WD40 underneath - in the mechanics of the knob, as it were - and then press it up and down a few times. The oven holds immediately the next time it is lit.

I think I've read here that WD40 isn't a lubricant but, whatever it is, it is the only way to mollify this mood. My oven deems 3-in-1 oil and PlusGas unacceptable offerings.

I would like to make a permanent fix. Is it as easy as replacing the thermocouple? From previous threads this seems like quite a straightforward job.

As always, thanks in advance.

 

[greeny]

Maybe I'm missing something, but I don't understand how spraying wd in the assembly fixes a faulty thermocouple. Albeit temporarily. If it was me I'd strip the assembly down and look to see what's causing the problem which appears to be "stiction" inside maybe.

 

[Alex_Blackwood]

Any one who sprays WD 40 near an oven is a candidate for a Darwin award!

 

[Aardee]

I'd be tempted to replace the assembly and thermocouple (assuming they're still available). I doubt they'd be prohibitively expensive.

 

[pcatterall]

As described it seems that the problem is in the knob and not the thermocouple. Take it to bits or keep using the wd 40 ( but near a flame!

 

[KompetentKrew]

Maybe I'm missing something, but I don't understand how spraying wd in the assembly fixes a faulty thermocouple. Albeit temporarily. If it was me I'd strip the assembly down and look to see what's causing the problem which appears to be "stiction" inside maybe.

When I Google images of thermocouples, they look like an actuator which is enclosed in a flexible tube.

So I assume the oil flows down the tube to whichever part is sticking. But I don't know, which is why I hoped to get advice from someone with experience of replacing a thermocouple.

I'd also rather know more about how they work before I start, rather than risk an unfinished job and no supper.

 

[KompetentKrew]

Any one who sprays WD 40 near an oven is a candidate for a Darwin award!

?

Mate, it's the application of a tiniest amount of lubricant to a mechanical part, before relighting the oven.

If you don't understand how something works, or my poor descriptions, you could manage to reply without being disrespectful. You don't seem to be contributing anything helpful here.

 

[KompetentKrew]

As described it seems that the problem is in the knob and not the thermocouple. Take it to bits or keep using the wd 40

What is the knob actuating, when you press it down, if not the thermocouple?

When you push down the knob, aren't you operating something mechanical, a lever or an arm, which holds the gas valve open?

 

[VicS]

When I Google images of thermocouples, they look like an actuator which is enclosed in a flexible tube.



So I assume the oil flows down the tube to whichever part is sticking. But I don't know, which is why I hoped to get advice from someone with experience of replacing a thermocouple.

I'd also rather know more about how they work before I start, rather than risk an unfinished job and no supper.

They are thermocouples. >>>> Electrical devices which produce a very small electrical current at a low voltage (a few mV) which when passed through a coil is just enough to hold open the valve which you opened by pressing the knob.

 

[Alex_Blackwood]

?

Mate, it's the application of a tiniest amount of lubricant to a mechanical part, before relighting the oven.

If you don't understand how something works, or my poor descriptions, you could manage to reply without being disrespectful. You don't seem to be contributing anything helpful here.

There is nothing mechanical about the thermocouple, it is simply a junction of two different metals which will cause a current, or millivolts, to flow when heated this will hold open the gas valve. That is what you do when you depress the knob. I would suggest that the valve is at fault and requires replacing, wouldn't hurt to replace both valve and thermocouple at same time.
Hope that helps? Yes I was bit sharp with original and sorry if it upset you but I still stand by the original statement. WD 40 is highly inflammable.
PS Your Thermocouple may not look like the one you googled!

 

[anoccasionalyachtsman]

Surely this is a thermoSTAT, and is a purely mechanical device?

 

[VicS]

Hello,

My oven, a 25-year-old Smev 300 series, has a peculiarity that it doesn't like to stay lit unless fed WD40 on a regular basis.

Like all modern gas stoves, the knob must be held down so that the flame can be lit, and then for a few further seconds until it is hot.

All the burners on the hob work fine, although it seems like one or two need holding down longer than others.

The oven will work fine for a few days at a time, and then one day the flame will go out as soon as the button is released. It doesn't matter how long it is held down, or seemingly how hot the oven's burner has got - as soon as the button is released the flame goes out. I've tried holding it for 30 or 60 seconds, I reckon, and when lubricated it works within 5.

I was instructed by the PO to remove the knob when this happens and to spray a little WD40 underneath - in the mechanics of the knob, as it were - and then press it up and down a few times. The oven holds immediately the next time it is lit.

I think I've read here that WD40 isn't a lubricant but, whatever it is, it is the only way to mollify this mood. My oven deems 3-in-1 oil and PlusGas unacceptable offerings.

I would like to make a permanent fix. Is it as easy as replacing the thermocouple? From previous threads this seems like quite a straightforward job.

As always, thanks in advance.

​

It sounds like a mechanical problem with the control valve. If Plus gas and 3 in 1 are not acceptable its probably because they contain or are mineral oil based. The same objection would apply to WD40
I might be tempted to try a silicone spray

BUT Check the thermocouple is correctly sited in the flame

also check the fitting at the control valve end............ Check the electrical contact is clean and the retaining nut is screwed in fully

 

[Boathook]

I had the same problem with my heating quite a few years back in that sometimes it stayed lit and went out others. Thermocouple was at fault. Sometimes they last years and others a year. Normally they just work.

 

[Bilgediver]

Dometic SMEV use both electrical and a bulb type mechanical device so might help if you find out which you have. The mechanical one will have what looks like a tube connected to the gas valve and the electrical one has a crimp wire connector. Both are easily tested. The electrical one probably gives a voltage when heated and the mechanical one will give movement to a plunger.

One fault all these devices can suffer from is incorrect positioning of the sensor element in the flame of the burner pilot flame. The sensor can get shifted by enthusiastic cleaning.

WD 40 is not a lubricant so I can understand that it will only be a temporary fix. It might be worth trying something more suitable as Vic has suggested or a light oil. You might find spares in a Caravan shop as these ovens are used in caravans and mobile homes.

 

[Iliade]

[Posts crossed]
The thermocouple produces a current which energises an electromagnet to keep the valve open.

If wd40 is fixing the problem, albeit temporarily, I would hazard that the issue is a build up of some sort on the face of the magnet. As it is almost certainly soft iron it is probably corrosion products. Friction within the valve would only help it to stay on so it is not working by lubricating something.

If you are confident (& competent) you could strip and clean the valve (in particular the electromagnet) and perhaps add a very thin smear of petroleum jelly or silicon grease to the iron face. What you don't want to do is add so much grease that it overcomes the spring!

First however I would try a new thermocouple as they only cost a few quid and are relatively uncomplicated to fit; The current produced does tail off as they age.

 

[Iliade]

Mechanical sensors are more typically used to modulate the main flame of an oven, i.e. They are normally the thermostat rather than the flame failure device, but I would never discount a designer going against established wisdom and practice.

 

[Boater Sam]

I bet the knobs are hitting the facia before they fully depress the valve spindles. Common fault.

Try lighting without the knob.

If that is so you need a bit of packing inside the spindle hole in the knobs.

 

[vas]

I don't see how that would work, I understand that the OP problem is that oven fires up and then switches off, as in no current from the thermowhatever to keep the valve open and gas flowing through.
fwiw, I'd go at dismantling knob assembly and cleaning contacts first as others mentioned above.
If not, one would need to find a matching thermothing, which probably wont be extremely easy (and definitely not the k-type thermocouple with the M5/M6 bolt/nut around in post #6)

cheers

V.

 

[greeny]

Don't know if this manual is any use - its for the range 300 and 400 ovens for marine and RV installation. Page 9 mentions thermocouples. It may not be the correct manual but worth a look. It does describe how to dismantle the parts which may be useful if it's the right manual.
Duplicate Data Plate; Servicing - smev CU311 User Manual [Page 9] | ManualsLib

 

[PaulRainbow]

I bet the knobs are hitting the facia before they fully depress the valve spindles. Common fault.

Try lighting without the knob.

If that is so you need a bit of packing inside the spindle hole in the knobs.

I'll take that bet, put me down for £100, what odds are you giving ?

From post #1

the flame will go out as soon as the button is released. It doesn't matter how long it is held down, or seemingly how hot the oven's burner has got - as soon as the button is released the flame goes out