SOT: Cooker question

I've seen this too. It may be that if the burner is hot, it generates convection air currents which prevent the gas/air mixture around the spark from being within the explosive range, which is actually quite narrow.

Needs clarification - does the gas flow but the spark fails - or does the gas not flow?

Whilst you're at it, how about some clarification on _which_ word your spill chucker objected to?

there's definitely gas coming out

and I can hear the igniters, but can't be sure if all of them are firing

igniter though it's happy with igniters

weird

tim

Good - that should have ruled out flame failure and general gas valve problems.

If you take the ring caps off (usually loose, for cleaning) you should be able to see the spark electrode.

It may be that if it is hot either the insulation on the supply wire is getting leaky or the ceramic of the electrode might have a crack which expands.

It's fairly new, and all of the rings do the same, so I don't think that this is an individual component failure. It's a design failure (or feature)

tim

You can hear the igniters, but none of them work?

What are you hearing - a spark?

Wild guess time:

The igniter is much like a spark plug, so it's operation depends on the gap between the terminal & the body of the burner.

When things are hot, expansion increases that gap.

Meanwhile all the igniters on the other burners, wired in parallel, are cool & thus their gaps are small.

Sparks happen on all the other burners & not on the only one you're interested in.

I missed this question

You hear it "click", yes it's a spark, but I have to put all the lights off to see it :-(

The gap is of the order of 2 mm - between two things which are not connected to each other

If either or both expands the gap will get smaller, not larger.

possibly

tim

have encountered electrodes fitted slightly too low before - they looked ok but the spark didnt light the gas in most cases

NT

I'd be surprised if the sparg gaps are all in parallel, connected to a common eht source. It's next to impossible to persuade a high voltage discharge to split itself across even 2, let alone 4, nominally identical gapped electrodes.

A more usual way to feed two spark gaps from a single eht coil is to use a double ended floating coil winding so that the two spark gaps are effective in series. This can be doubled up by using a pair of such ignition coils with their low voltage primaries connected in series to the common low voltage pulse source.

Alternatively, I think piezo transformers might offer a way of generating 4 independent spark voltage sources but I'm only hazarding a guess here. I'll leave the googling on this subject to you (the methodology will certainly have some bearing on the failure mechanism you're experiencing).

That's usually the case. A single ignitor button, ergo sparks at all burners.

The one I repaired on my parents Smeg hob is an EHT transformer which has a secondary winding per sparc gap.

(The circuit board got wet when a carpender put a screw through one of the heating pipes upstairs. Fortunately, the EHT transformer was fully potted and not damaged by immersion, but several of the components on the circuit board had to be replaced, and copper tracks cleaned and repaired.)

The Smeg one wasn't piezo. It just leaks charge into capacitor from mains through a rectifier and resistor, and has a gas discharge spark gap to discharge that capacitor across the transformer primary when the capacitor voltage reaches the breakdown voltage of the gas discharge spark gap. The charge/discharge cycle repeats if you keep the button pressed.