Ian Posted February 21, 2015 Share Posted February 21, 2015 This one has me confused...The ones on my hob operate the same as most others, I think. Turn to adjust the flame, push down (against a spring) to ignite.I bought a replacement set of universal knobs. They fit, and most of the time work properly. Occasionally, the gas refuses to stay lit, for no apparent reason - it was working 5 minutes ago, now it isn't.Some form of safety cut out perhaps? But why sometimes and not others?Any ideas welcome, otherwise I'll have to buy proper replacementsCheers Link to comment Share on other sites More sharing options...
Quillan Posted February 21, 2015 Share Posted February 21, 2015 Firstly all modern gas hobs must shut off automatically if the flame goes out, been that way for a few years now. It is always better to get the proper knobs and they are easy, if not expensive, to find. If the hole in the knob is too deep it might be that the shaft only goes in enough to allow you to turn the knob but not enough to activate the interlock on the flameout detector. You could try putting something in the whole so the shaft does not go in so deep. Of course it might just be coincidence and that the flameout device has also failed. Hope that helps, other than that I don't have a clue. Link to comment Share on other sites More sharing options...
Chancer Posted February 21, 2015 Share Posted February 21, 2015 It is something along the lines of what Quillan says, the thermocouple if working holds open the gas valve but there is also some interlock on the knob mechanism who's function I dont understand (and that bugs me!).I had a similar intermittent problem with one burner on the new gas hob that I used initially, turned out not to be the thermocouple at all but something on the knob mechanism as when I tightened further the backnut and realigned the body a couple of degrees it functioned perfectly thereafter.Wish I could tell you what the problem is exactly but you are on the right track, try swopping the knobs around and see if the problem follows them, compare all the shafts, the mechanisms, their alignment and protrusion carefully and make sure they are all tightened properly. Link to comment Share on other sites More sharing options...
Ian Posted February 21, 2015 Author Share Posted February 21, 2015 Mr Quillan, sir, it looks like you were right.I've just re-seated the knobs, this time with a little piece of 2.5mm cable down the hole, and they seem to be working properly. If they're still working after a few days, I'll make the adjustment permanent.(One of the reasons I choose these, rather than exact replacements, is that the original knobs are round, with printed markings. The markings have worn off, so they are hard to use. These, on the other hand, are rectangular.)Cheers Link to comment Share on other sites More sharing options...
Chancer Posted February 21, 2015 Share Posted February 21, 2015 Great result, strange that it could push down far enough to pass the gas to initially light, but it sounds so so similar to the problem that I had, and there is nothing I hate worse than fixing a problem without understanding what it was and how I have resolved it.Mine was a new hob with the makers knobs.The people that I bought mine from was a déstockage place not 500m up the road from me, the manager is a neighbour, lives not more than 50 metres from me and he passes my place 4 times a day going to and from work.He refused point blank to come and look at it, I didnt even want him to fix it, just give me an idea of what I could do, it was by then encastré in the old bar counter and silicone sealed, no he refused point blank, insisted that I returned it to them in its original packaging with the original reciept and leave it with them for up to a month, at the time I was living in a tent indoors and being able to cook using the old bar was the only home comfort that I had, I wasnt going to give that up for a problem with one burner.It was my second week here and a short sharp lesson in what I could (not) expect in regards to Customer service. Link to comment Share on other sites More sharing options...
Ian Posted February 21, 2015 Author Share Posted February 21, 2015 I think the knob extends a (very) small amount too far downwards - sometimes it fouled the valve body (and didn't work), sometimes it didn't. We shall see.Yeah, I know what you mean about SAV. It's improving, but very slowly, which is a pity. I'd like to buy everything I need in France, but with some things I can't take the risk - I buy from the UK. My french isn't good enough to argue the toss with some bolshie shop assistant.On the other hand, there are LOTS of good things about living in France, which is why I'm here. The rough with the smooth.Cheers Link to comment Share on other sites More sharing options...
lindal1000 Posted February 21, 2015 Share Posted February 21, 2015 I never knew you could get gas ones. I thought they only made chocolate and plain? Link to comment Share on other sites More sharing options...
dave21478 Posted February 23, 2015 Share Posted February 23, 2015 The thermocouple is basically an electro magnet that holds a plunger inside the gas valve open. Pressing the knob down physically pushes a plunger that stops the gas flow against the body of the electro magnet, allowing the gas to pass. The flame heats the end of the thermocouple, generating a small current which energises the electro magnet so the plunger stays held open. Problems arise when you fiddle with your knob! if the knob hole is too deep or the knob skirt is too long, the plunger doesnt get pushed fully in. This is enough to let gas flow and the ring to light, but the electro magnet is not powerful enough to hold the plunger unless it is in direct contact. Something wedged in the bottom of the knob hole usually does the trick.Another problem is when the nut where the thermocouple joins the valve block becomes loose, this introduces enough of a gap for the electro magnet to not hold properly again. It usually needs a 7 or 8mm spanner, just make sure its nice and tight. On older cookers, the wiring coil in the electro magnet fails - generally speaking these are a fairly standard size so if your valve block comes apart, the coil can be removed, its a wee cylindrical cartridge with the plunger and an o-ring sticking out of the end.electro magnet...[img]http://i00.i.aliimg.com/img/pb/658/884/422/422884658_904.jpg[/img]thermocouple. One end in the flame, the other end screwed into the valve block making good contact with the end of the electro magnet.[img]http://i00.i.aliimg.com/img/pb/225/664/425/425664225_994.jpg[/img] Link to comment Share on other sites More sharing options...
Ian Posted February 24, 2015 Author Share Posted February 24, 2015 dave21478,A very clear explanation. I understand much better now how the valves work (and why mine didn't sporadically).Thanks for that Link to comment Share on other sites More sharing options...
Dave sting Posted February 25, 2015 Share Posted February 25, 2015 Apart from the mechanical problems there is also the possibility of the flame not heating the end of the probe and generating the small current needed to operate the electro magnet to allow the gas through, this can be caused by a poor flame towards the probe due to blockage in the burner of the main flame, normally stopping initial operation, or blockage of the secondary flame, this part of the flame if blocked can cause the problem of flame lift and make the probe drop out after a pan is put on the seemingly good flame, both of these probs can be cured by careful cleaning of the burner. Link to comment Share on other sites More sharing options...
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