Smev oven - will replacing the thermocouple fix this?

[anoccasionalyachtsman]

I'd like to thank @KompetentKrew for starting the thread. I'd never heard of a thermopile before. (I couldn't accept that a thermocouple could produce enough Watts to hold a valve open - led to reading further and lighting upon the thermopile - a stack of thermocouples).

 

[VicS]

I'd like to thank @KompetentKrew for starting the thread. I'd never heard of a thermopile before. (I couldn't accept that a thermocouple could produce enough Watts to hold a valve open - led to reading further and lighting upon the thermopile - a stack of thermocouples).

If you cast your mind back to your schoolboy physics.

Watts = power and power = the rate of doing work

Work is done when a force moves through a distance.
In just holding the valve open the force doing so is not moving through any distance so, in theory , no work is being done therefore the power required is zero. You do the work when you push the knob in to open the valve

What you do need is a force great enough to hold the valve open. This is achieved by passing the tiny current though a coil. The strength of the magnetic field produced by the coil being a function of the the current and the turns density.

Tiny current x many turns = a magnetic field strong enough to hold the valve open

The tiny amount of power involved, mV x mA is only µW and will be lost as heat.

 

[Alfie168]

If the pilot stay lit after you have sprayed WD40 into the gas tap then I'd beta penny to a pound its the gas tap lacking lubrication and not the thermocouple that is less likely to be faulty...though it may be getting that way if old. You need gas tap grease such as molycote. Then watch this.....

On the other hand it could be the WD40 temporarily making a good electrical contact from the thermocouple to the gas valve...so tighten the thermocouple retaining nut at the gas valve end or alternatively take it off and clean up the contacts with fine emery then reassemble nice and snugly.

 

[KompetentKrew]

Thanks very much for all the replies in this thread - they've really helped me visualise the problem.

I hadn't understood exactly what a thermocouple was or how it worked, only seen them mentioned when searching threads of this type.

For reasons I can't quite articulate, I think @anoccasionalyachtsman and @Iliade are correct, and that the oven safety must be operated by a thermostat and not a thermocouple.

A replacement thermostat is much more expensive than a thermocouple (at least £100 - more than the oven itself is worth), but hopefully it can be repaired.

I'll investigate further in due course, but probably not immediately.

 

[anoccasionalyachtsman]

Thanks very much for all the replies in this thread - they've really helped me visualise the problem.

I hadn't understood exactly what a thermocouple was or how it worked, only seen them mentioned when searching threads of this type.

For reasons I can't quite articulate, I think @anoccasionalyachtsman and @Iliade are correct, and that the oven safety must be operated by a thermostat and not a thermocouple.

A replacement thermostat is much more expensive than a thermocouple (at least £100 - more than the oven itself is worth), but hopefully it can be repaired.

I'll investigate further in due course, but probably not immediately.

No, somewhere down the thread I edumicated myself and am now in the thermocouple camp - although I'm also with those that think you have a mechanical problem that a good clean might fix.

 

[RupertW]

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

From post #1

I think you are saying that you don’t think it’s the knob?

Packing the knob is actually the standard fix for an Eno stove where the ring or oven goes out as soon as the button is released - as happened to mine on one ring and the oven. I was advised to put a bit of sticky tape round the metal bit then put the knob back on over it. It worked immediately on both.

Edit: I am slightly embarrassed to say that as I had a dozen other waiting jobs I didn’t check the logic behind the fix, just accepted that it worked and moved on.

 

[KompetentKrew]

No, somewhere down the thread I edumicated myself and am now in the thermocouple camp - although I'm also with those that think you have a mechanical problem that a good clean might fix.

See this comment though.

 

[KompetentKrew]

I think you are saying that you don’t think it’s the knob?

Packing the knob is actually the standard fix for an Eno stove where the ring or oven goes out as soon as the button is released - as happened to mine on one ring and the oven. I was advised to put a bit of sticky tape round the metal bit then put the knob back on over it. It worked immediately on both.

Edit: I am slightly embarrassed to say that as I had a dozen other waiting jobs I didn’t check the logic behind the fix, just accepted that it worked and moved on.

I don't see how it can be just the knob either, but I will test that next time it happens. I would be delighted if the fix were so easy!

 

[DownWest]

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.

If the knob is not going in fully enough to get the valve seat in contact with the electromagnet, the flame will light, but go out when the knob is released. As above, the electomagnet is a holding unit, not enough power to pull the valve in.

 

[Boater Sam]

The thermocouple generates a tiny current only enough to hold the magnet in, not pull it in. So if the magnet is not fully pushed onto the solenoid armature because the knob hit the facia, then it will not stay attracted when you let go.
Believe, this is the main cause of this problem, take the knobs off and try it.

 

[VicS]

Thanks very much for all the replies in this thread - they've really helped me visualise the problem.

I hadn't understood exactly what a thermocouple was or how it worked, only seen them mentioned when searching threads of this type.

For reasons I can't quite articulate, I think @anoccasionalyachtsman and @Iliade are correct, and that the oven safety must be operated by a thermostat and not a thermocouple.

A replacement thermostat is much more expensive than a thermocouple (at least £100 - more than the oven itself is worth), but hopefully it can be repaired.

I'll investigate further in due course, but probably not immediately.

The thermocouple is the "safety" device. It senses whether or not there is a flame. If the flame goes out ( gets blown out for example) the lack of electrical output from it results in the gas supply to the burner being shut off.
When there is a pilot light the thermocouple sesnses the pilot light flame.

The thermostat controls the oven temperature by regulating the gas flow. As the set oven temperature is reached the thermostat will reduce the gas flow to the burner.

 

[KompetentKrew]

take the knobs off and try it.

I promise you I will

 

[Boater Sam]

Thermostat has nothing to do with the pilot flame, only controls the main burner. If the end of the thermocouple looks eroded and not nice and round, it may be faulty but unlikely.

 

[Alfie168]

Thanks very much for all the replies in this thread - they've really helped me visualise the problem.

I hadn't understood exactly what a thermocouple was or how it worked, only seen them mentioned when searching threads of this type.

For reasons I can't quite articulate, I think @anoccasionalyachtsman and @Iliade are correct, and that the oven safety must be operated by a thermostat and not a thermocouple.

A replacement thermostat is much more expensive than a thermocouple (at least £100 - more than the oven itself is worth), but hopefully it can be repaired.

I'll investigate further in due course, but probably not immediately.

Ovens normally have a thermocouple as a flame failure device and a thermostat as a heat control device. Yes the thermostat is usually far more expensive as it does more.

 

[HunterWanderer]

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

From post #1

I replaced the thermocouple on mine and it made no difference. The fault was the spindle wasnt being deprest sufficently for the valve to latch. Added a spacer to the spindle as suggested and now perfect.
Worth a try!

 

[PaulRainbow]

I replaced the thermocouple on mine and it made no difference. The fault was the spindle wasnt being deprest sufficently for the valve to latch. Added a spacer to the spindle as suggested and now perfect.
Worth a try!

I shall await the results from the OP testing this with eager anticipation

 

[KompetentKrew]

The thermocouple generates a tiny current only enough to hold the magnet in, not pull it in. So if the magnet is not fully pushed onto the solenoid armature because the knob hit the facia, then it will not stay attracted when you let go.
Believe, this is the main cause of this problem, take the knobs off and try it.

I replaced the thermocouple on mine and it made no difference. The fault was the spindle wasnt being deprest sufficently for the valve to latch. Added a spacer to the spindle as suggested and now perfect.
Worth a try!

This makes no sense to me, because this evening this fix worked.

The oven failed to stay on two or three times, so I left the dial at max, removed the knob and pressed it all the way down as I lit it. It did feel like it can go down further with the knob off, and this time it stayed lit.

A couple of hours later, I thought I'd check it again before making this post and it continued to work with the knob still on. ?

 

[Daverw]

Is it possible that the last time the knob was refitted it was slightly higher than the previous time, it could be even a fraction of mm is stopping the gas valve opening.. on hours some knobs are very slightly proud of others when all the valves are exactly the same height

 

[VicS]

This makes no sense to me, because this evening this fix worked.
The oven failed to stay on two or three times, so I left the dial at max, removed the knob and pressed it all the way down as I lit it. It did feel like it can go down further with the knob off, and this time it stayed lit.
A couple of hours later, I thought I'd check it again before making this post and it continued to work with the knob still on. ?

Time to try what Boater Sam suggested back in #17
and Hunter Wanderer said in #35

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 replaced the thermocouple on mine and it made no difference. The fault was the spindle wasnt being deprest sufficently for the valve to latch. Added a spacer to the spindle as suggested and now perfect.
Worth a try!

 

[VicS]

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