Gas hob (1 Viewer)

[Pw9crab9]

Hi can any one help smev gas hob 2 burners work ok the other will light but when you release the button the gas goes out

 

[Diabalo]

I have a Thetford and had the same problem with my grill mine doesn't have a conventional Thermocouple it's done via magnets in the knob, so I had to have a new one. Yours may be the same if you cant see a thermocouple by the flame.

 

[DP+JAY]

Usually a bad connection on the wire underneath, if you can access the underside give the terminal on the offending burner a wiggle. Works for us.
DP

 

[Odd job]

It sounds like the thermocouple but it could be the knob, although not likely, try taking the knob off and pushing the shaft in as you light it, if it still goes out it's the thermocouple. Check the tip of the thermocouple is in the flame, if so it wil need replacing

 

[RustyRuss]

Also check that the tip of the thermocouple isn’t damaged/burnt through.

^{_{Subscribers  do not see these advertisements}}

 

[Fragle]

It sounds like the thermocouple but it could be the knob, although not likely, try taking the knob off and pushing the shaft in as you light it, if it still goes out it's the thermocouple. Check the tip of the thermocouple is in the flame, if so it wil need replacing

That’s right.
Sometimes we used to roll a small amount of paper and put it into the knob. When pressed it would make a better contact the hole may be too deep in the knob. Best check is using the knob off another burner. If ok with that then put something in to allow it to press the shaft making it contact with the thermocouple.
Also at burner make sure thermocouple is in the flame.

 

[Pausim]

I have a Thetford and had the same problem with my grill mine doesn't have a conventional Thermocouple it's done via magnets in the knob, so I had to have a new one. Yours may be the same if you cant see a thermocouple by the flame.

How do magnets in the knob sense the flame?

 

[Diabalo]

How do magnets in the knob sense the flame?

No idea how idea how it works but I do not have the normal thermocouple just the Pizzo spark probe by each gas ring, maybe uses that somehow. When the engineer fixed it under warranty I'm sure I remember him saying the cut off was part of the control valve and worked by magnets or it may have been electro magnetic.

 

[Diabalo]

Pausim You got me wondering so did a bit of digging and got the below of internet. I'm confused as I'm sure my cooker hob rings don't have traditional thermocouples, well none I can see when I lift the lid. Anyway I was correct about magnets albeit electro magnet.

How the system works,:

There is a valve within the tap assembly that contains a coil, this coil becomes a magnet when current from a heated thermocouple is passed through it, this is why when you light the burner and release the tap immediately it will go out.

Holding down the tap for 30 secs or so has to be done to hold the valve open until the magnetic field is sufficient to hold it open, the thermocouple produces around 25mv to 35mv DC ( millivolts ) open circuit and about 15mv to 20mv closed circuit.

Presuming your thermocouples are single wire, current flow when the thermocouple is heated is through the wire to coil in the tap assembly, the return, earth is through the tap body, hob and to the thermocouple body.

 

[Odd job]

Pausim You got me wondering so did a bit of digging and got the below of internet. I'm confused as I'm sure my cooker hob rings don't have traditional thermocouples, well none I can see when I lift the lid. Anyway I was correct about magnets albeit electro magnet.

How the system works,:

There is a valve within the tap assembly that contains a coil, this coil becomes a magnet when current from a heated thermocouple is passed through it, this is why when you light the burner and release the tap immediately it will go out.

Holding down the tap for 30 secs or so has to be done to hold the valve open until the magnetic field is sufficient to hold it open, the thermocouple produces around 25mv to 35mv DC ( millivolts ) open circuit and about 15mv to 20mv closed circuit.

Presuming your thermocouples are single wire, current flow when the thermocouple is heated is through the wire to coil in the tap assembly, the return, earth is through the tap body, hob and to the thermocouple body.

That is how a thermocouple works, if your hob doesn't have a thermocouple then it will have a flame sensing ingnition electrode, do you have to hold the knob in when you light the burner?

^{_{Subscribers  do not see these advertisements}}

 

[Diabalo]

That is how a thermocouple works, if your hob doesn't have a thermocouple then it will have a flame sensing ingnition electrode, do you have to hold the knob in when you light the burner?

Yes I have to push it in turn it then press the spark button don't think I have to hold it in once alight.

 

[Odd job]

Yes

Then it's a thermocouple. A thermocouple has to heat up on order to generate the electricity to energise the electro magnet, an electronic system is instant,also I have not seen that type of control on a hob.
Your hob will have a thermocouple, it may just be hidden under the burner cap.

 

[Winger]

Usually a bad connection on the wire underneath, if you can access the underside give the terminal on the offending burner a wiggle. Works for us.
DP

Likewise result for me and it was easy access after I removed the cutlery drawer.
I had no idea what I was looking for but just disconnected and reconnected the spade terminals and it worked ever since

 

[Pw9crab9]

Ok thanks for all replies just back from Germany so will look at it next week watch this space I think it’s a thermocouple

 

[tinkertaylor]

It sounds like the thermocouple but it could be the knob, although not likely, try taking the knob off and pushing the shaft in as you light it, if it still goes out it's the thermocouple. Check the tip of the thermocouple is in the flame, if so it wil need replacing

Our oven did exactly this, removed the knob and pushed the shaft in using then lit the flame, held the shaft in for 5 seconds then bingo the flame stayed on.

That’s right.
Sometimes we used to roll a small amount of paper and put it into the knob. When pressed it would make a better contact the hole may be too deep in the knob. Best check is using the knob off another burner. If ok with that then put something in to allow it to press the shaft making it contact with the thermocouple.
Also at burner make sure thermocouple is in the flame.

Yep, Packed the back of the knob and ours now works

^{_{Subscribers  do not see these advertisements}}

 

[scotzsue]

Resurrecting this thread, 2 of our dometic burners work fine but on the third we cant hear or smell any gas coming through, it's the big main burner, we can manage with 2 but this was quicker for boiling a kettle and more suitable for larger pans.
any idea of the cure assuming it is a blocked jet which we are having difficulty accessing.

 

[scotzsue]

Can't see this on the forum had to search.