One element not heating. Where do I find a serviceman in Sutherland shire.

YOU HAVE THE RIGHT IDEA A PROFESSIONAL REPAIR SERVICEMAN

If it is similar to the VE260 model, this induction type of cook top is very old. 22 - 23 years if it came with the home when it was built.
I can only offer basic suggestions of which you already probably know.
These induction type cook tops rely on the pan or skillet to be magnetic like stainless steel. If the bottom of the pan has any buildup of residue, this will dramatically reduce the efficiency of the unit.
If the pans are immaculate, then the electronic elements that produce the magnetic induction to heat the coils must be weak. As old as the unit is, it is probably not feasible to have 3 of the elements repaired....
A new top can be purchased much cheaper. Consult Consumers Reports for unbiased product reviews for your best reviews. As a final suggestion, find someone who is qualified to use an electrical multimeter to read the current on both sides of the power receptacle to ensure that your voltage is 230V. A loose connection on the receptacle can cause the elements to have the same result.
Although I can imagine you have already done everything above, I just wanted to send you what I can offer.

The problem is most likely in the element in one of the coils, if they are the tube type and look like pencil thick heating elements, they can develope a short circuit inside them. The actual heating wire is encased with ceramic filler and then put in that tube. The heating wire moves when it gets hot and can work its way to the case and cause a short. Unhook the power from the whole unit and use the meter to check the rersistance of the coils between the heating element and the case

I have the same issue.

Go back and recheck your wiring. It sounds like you have the burners wired in series together.

age is factor see if you can get replacement part for it call used appliance store

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Either the elements are going out or the controlls for the burners are getting croded contacts. Best bet would be to replace both and go for another 7 years :-)