Gas Hob rings not staying lit.

[Harry Bloomfield]

Four ring stainless hob, 1x large; 2x medium; 1x small rings, bought 3 years ago, with a 5 year guarantee - except I couldn't find the receipt or remember where it was bought from, just an online source.

Soon after I installed it, the large ring, then the smallest ring, began giving problems getting them to stay lit, the valves were not reliably holding in once lit - a bit of a lottery.

Yesterday evening, I got a roundtuit. I wasted ages, struggling to get the entire hob out of the worktop, thinking access would be from below. I was WRONG, what wasn't obvious was that the entire top plate cover could be removed without disturbing the actual hob from the worktop. Remove cast iron pan supports, the control knobs, then two screws either side of each burner and off it came, giving full access to the entire gubbins - the work of minutes, not the hour I had spent so far getting the hob out.

There was nothing obviously amiss at all, so it was pointing towards the individual gas valves being a bit iffy, or the 'thermocouples'. Undetered, I disconnected the 'thermocouples' from the gas valves, cleaned up the contacts and reassembled and tested. Now they all work fine. There was some dirt from some where on the contacts, but no obvious way for it to get in there other than during manufacture. The base panel, pipework valves etc. were quite clean. I rested again this morning and all still working fine, the valves hold in a fraction of a second after lighting.

I called them 'thermocouples' because they are not like any thermocouple I have ever seen before, hence my posting this. The sensor ends looked like TC's, but they each had their own separate earth wire. The TC seemed to have a a tiny tube, then at the end they had a small plastic unit (A), with a pin which pushed into the tube end and a spring contact where it connected to the valve. A sleave nut fitted over the end of the tube flange, item A and tightened onto the valve. A seemed to have 'something' inside the clear plastic tube.

What sort of 'TC' is this, for holding the valves in please? I have heard of a system which uses a voltage generated by the gas itself burning. Might this be one of those?

[Andy Burns]

Usually called flame failure devices, but they are thermocouples.

[GB]

We converted my old office into two flats. The builder supplied what I presume were the cheapest hobs he could find. Both stopped working because of the flame failure devices within a couple of years. I'm sure this was a manufacturing fault similar to what you found.

We just replaced the pieces of junk.

[Alan Dawes]

You don't need the receipt just evidence of having purchased the item. Look at your old bank / credit card statements from around the time you bought it and this will give evidence of the purchase and also the account of the seller. Then look at your emails from that time as you should have an online email receipt from the seller. Use a search engine to find the contact details and invoke the 5 year guarantee. - sorted or perhaps not? :-)

Alan

[F Murtz]

Check that the pipe delivering gas is big enough to supply the flow needed for that particular hob, which may be more than the previous one.

[Weatherlawyer]

Why are you asking after you went to the bother you did? I think you will find that the thermocouples are designed so that your gas will NOT stay lit unless you reassure the stove that you mean business. It is a safety device that makes you keep your finger on the button long enoug h for it to believe you (seven seconds I was told.)

[Harry Bloomfield]

Alan Dawes a écrit :

It was a purchase made by my deceased partner, so impossible to trace now. I oft find it easier to at least attempt to fix things myself, than invoke warranties. In this case it was an easy fix.

[Harry Bloomfield]

F Murtz a écrit :

It is more than big enough, it feeds the double oven and boiler - the problem was evident with no other gas in use. It was simply the flame failure system at fault.

[Harry Bloomfield]

Weatherlawyer a écrit :

I am well aware of their purpose, I was just puzzled by the device used

- not a TC type I have seen before (see my quote below).

'I called them 'thermocouples' because they are not like any thermocouple I have ever seen before, hence my posting this. The sensor ends looked like TC's, but they each had their own separate earth wire. The TC seemed to have a a tiny tube, then at the end they had a small plastic unit (A), with a pin which pushed into the tube end and a spring contact where it connected to the valve. A sleave nut fitted over the end of the tube flange, item A and tightened onto the valve. A seemed to have 'something' inside the clear plastic tube.

What sort of 'TC' is this, for holding the valves in please? I have heard of a system which uses a voltage generated by the gas itself burning. Might this be one of those?'

[Harry Bloomfield]

Weatherlawyer a écrit :

They usually say hold it in for 10 seconds. The hob in my caravan only needs a fraction of a second, as does the now fixed kitchen hob.

[harry]

All thermocouples generate electricity by means of a joint of dissimilar metals being heated. Usually concentric. The tiny voltage holds a solenoid valve open. Takes a few seconds to heat up. Flame failure means the valve shuts.