Gas hob thermocouple

Gave the Nuevo a shake-down this morning. Discovered that one gas burner will not remain on, so I'd appreciate advice, please. Here are details: Thetford Caprice MkIII, front left gas hob ignites whilst holding in the knob but - even after holding it in for 20+ seconds - it goes out as soon as I stop pushing. Normal flame; other hobs are fine.

I unscrewed the cover plate and the gas diffuser and looked at the thermocouple, but that's all I dared to do. It looks the same as the other 2.

I've searched the Forum, but the only return for "thermocouple" is Libraryman2's thread about the grill.

I'm assuming that this is a thermocouple issue?  What should I do, please?

Cymro

Cymro wrote:Gave the Nuevo a shake-down this morning. Discovered that one gas burner will not remain on, so I'd appreciate advice, please. Here are details: Thetford Caprice MkIII, front left gas hob ignites whilst holding in the knob but - even after holding it in for 20+ seconds - it goes out as soon as I stop pushing. Normal flame; other hobs are fine.

I unscrewed the cover plate and the gas diffuser and looked at the thermocouple, but that's all I dared to do. It looks the same as the other 2.

I've searched the Forum, but the only return for "thermocouple" is Libraryman2's thread about the grill.

I'm assuming that this is a thermocouple issue?  What should I do, please?

Cymro

Make sure that the thermocouple is receiving the warm part of a flame. A bit of dirt on the burner can deflect or diffuse it.

We recently had a new home gas cooker the installer couldn't get one burner to remain on even with a pan on the ring, he recommended getting the manufacturer out and left me with it.

I took off the ring and could see a very small lip on the slot that sits in the thermocouple position, one stroke of a small file cured it.

Sounds like the thermocouple has failed

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To access the part you will need to 

Unplug the 3 pin mains power plug underneath the cooker and turn the gas isolator tap off

Remove all the black burner covers and diffusers (no need to remove the electric hotplate)
Pull all the control knobs off
Remove the front fascia panel, it’s held on with two screws and 2 brass nuts
Remove the 2 screws from the front trim that holds the large black enamel base tray in position
Remove the other 2 screws from the rear hinge trim above the enamel base (no need to remove the hinges)
Lift the enamel base up at the front and the base will lift out

The thermocouple is simple to replace

There’s no need to disturb any gas fittings

Last week I dismantled the top of our cooker to remove the metal trim that supports the full weight of the cooker, the rear supporting brackets were broken.
I welded and reinforced the brackets and had the 5 pieces of trim shot blasted and powder coated


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Spanner: that's wonderful!   So clear!

I'm most grateful. Now to pluck up courage... !

Thank you very much indeed.

Cymro

We had that problem on our Adria back in 2009.

We were down south and took it in to Southdown who sorted it in 10 minutes.

I don't think they could've replaced the thermocouple in that time. I suspect they just cleaned the gas 'holes' on the burner, ensuring that the flame covered the sensor and all seemed well afterwards.

Cymro wrote:Spanner: that's wonderful!   So clear!

I'm most grateful. Now to pluck up courage... !

Thank you very much indeed.

Cymro

You’re welcome, pm me if you need any help

If you proceed with the repair remember to check that the silver coloured frame is still fastened to the black side frames as the rear corner fixing brackets are pathetically weak, I often thought it sounded like the cooker was trying escape when I hit a big pothole in the road

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Chris

Do check the burner cap location carefully first. That used to happen a lot to one of the burners on the hob in our last house. It affected ignition or staying on.

I'm really most grateful to you all, especially Spanner, for your help.

Having again checked the burner groves etc were clear, I sought the part - only to find that delivery is at the end of April.  I had booked the van for its habitation service for the firsT week of April and the firm said they could source the part by then. So I'm afraid that I chickened out ( being very wary of gas ).  

I remain most grateful for your help. I'm sure others, bolder than me, will benefit from it.

Cymro

Don't apologise, Cymro, you're doing the right thing.

I'm fairly confident dealing with basic gas appliances, as I sold control and test instruments (including thermocouples) into the boiler manufacturing and service industries for decades.

However, I think of gas in the same way as I think of the sea when I go out on my small boat - treat it with respect and if in doubt when out of your depth, call in the experts.

Just an update: you may recall that I raised this thread because one of the hob burners wouldn't stay alight. I assumed that the thermocouple needed to be replaced. Although Spanner very kindly told me how to do the job (I repeat my thanks) I chickened out and left it to be done with the annual hab service.

I'm glad I did. It wasn't the thermocouple, but what was described to me as the gas valve. Anyway, all now sorted.

Thanks to you all.

Cymro

Thanks for coming back with the update.

Glad you had a safe and satisfactory outcome. 

Interesting, around the same date our new kitchen at home was being fitted. The following day 2 of the burners on the hob refused to stay alight. Checked the burners and gas flow and all seemed ok. Being brand new got onto to Hotpoint Service who very promptly arrived checked it and replaced the knobs on the two suspect controls.  When I queried this he said it was suspect knobs ??? anyway its worked since.
Low and behold went in the van to check a few things and one of the knobs on the hob wasnt operating. Our local Thetford Service guy didnt have stock and put me onto Leisurespares at Boroughbridge who supplies very quickly ( certainly matching Amazons deliveries!!!) so that hob also works now.

These things work for years but in the spacxe of a month you hear of 3 !!

Gosh, Roli, you make it sound easy! Was the faulty knob a simple detach /attach job? And if so, was that which my service chap calls the "gas valve" or is that different? I was charged £52 & vat for the valve and a further £50 plus vat to fit it. I hope that's different from the knob at the front!

Incidentally, I feel totally foolish: this morning went into the van and saw that the Truma control panel was blank. 12v circuits all OK; ditto 240v. My Truma panel has a rotary button which you use to select the function which you want to set e.g gas or elec; water heater temp / off; air heater temp / off etc. Totally blank. Gave the button a few stabs - nothing. Phoned dealer. Assured it was OK when I collected it yesterday pm.  

Drove 15 miles there this morning. Man came into van - pressed button .... and held it in for 2 seconds - panel came alive and all OK!

My face is tomato red with embarrassment!

Cymro

The gas valve is a bit more complicated than the knob!

It controls the flow from the gas supply to the burner. Inside it has a spring loaded electro-magnetic valve actuator. Depending on the type of hob you have, when you hold in the knob and light the gas, once the thermocouple tip heats up in the flame it generates a small (milli)voltage which is enough to overcome the spring tension when you release the knob, thus keeping the gas valve open. Should the flame fail (or the thermocouple become faulty) then this voltage ceases and the spring actuator snaps the valve shut, safely turning off the gas supply to the appliance.

Thanks, Roger - I didn't know any of that.

The story wasn't quite over: just been out to the van to put a few things back, and I heard a faint "click". I recognised it as the fridge thermostat switching on or off. After checking it, the service people had left the fridge on Auto and it's been running on gas for the last 20 hours..... !  

Cymro

marconi wrote:

Cymro wrote:Gave the Nuevo a shake-down this morning. Discovered that one gas burner will not remain on, so I'd appreciate advice, please. Here are details: Thetford Caprice MkIII, front left gas hob ignites whilst holding in the knob but - even after holding it in for 20+ seconds - it goes out as soon as I stop pushing. Normal flame; other hobs are fine.

I unscrewed the cover plate and the gas diffuser and looked at the thermocouple, but that's all I dared to do. It looks the same as the other 2.

I've searched the Forum, but the only return for "thermocouple" is Libraryman2's thread about the grill.

I'm assuming that this is a thermocouple issue?  What should I do, please?

Cymro

Make sure that the thermocouple is receiving the warm part of a flame. A bit of dirt on the burner can deflect or diffuse it.

We recently had a new home gas cooker the installer couldn't get one burner to remain on even with a pan on the ring, he recommended getting the manufacturer out and left me with it.

I took off the ring and could see a very small lip on the slot that sits in the thermocouple position, one stroke of a small file cured it.

Just back from a few days in Northumberland where one of our hob burners failed, still got a flame but very small. Found this thread after much searching, sometimes knowing the key words is tricky .

Have dismantled burner, cleaned all the rubbish out, and filed end of thermocouple. All working fine now and no need for trip to dealer.

Thanks guys.

Picked up van after Habitation service recently, to be told that I needed a new regulator for one of the gas hobs on my Thetford cooker. Gas lights, but won't stay alight when the knob is released after a short while.  "Funny" I thought - "it was working fine when last used - admittedly 5 months ago". Big delay on order, so the new one hasn't arrived.

First overnight stay yesterday at Malvern. Friend also there in his Clubman. I mentioned the hob problem, and he said he'd had exactly the same problem recently. So he pulled off the knob on the front of our Thetford, and brushed any debris around the spindle. Pushed the spindle in a few times to activate the spring. Put knob back. Working perfectly.

So I'm going to clean the other knobs / spindles to ensure that they aren't clogged. Maybe a little squirt of silicone lubricant might help.

Who'd have thought!

Cymro

marconi wrote:
Make sure that the thermocouple is receiving the warm part of a flame. A bit of dirt on the burner can deflect or diffuse it.

We recently had a new home gas cooker the installer couldn't get one burner to remain on even with a pan on the ring, he recommended getting the manufacturer out and left me with it.

I took off the ring and could see a very small lip on the slot that sits in the thermocouple position, one stroke of a small file cured it.

I've known gas men who would have charged £150 for doing that. well done Marconi, you are not only good at transAtlantic communications, you can fix a gas hob!

Cymro wrote:

I'm glad I did. It wasn't the thermocouple, but what was described to me as the gas valve. Anyway, all now sorted.

Thanks to you all.

Cymro

They must mean the valve behind the control knob, what would be called a tap if it was controlling water. Yes, they can get a little bit of dirt or grease in them that causes the fault you describe, but it's very rare. My first guess would certainly have been the thermocouple.