Just fitted a new top element to a Bosch oven as the previous inner ring was not working. The new element shows same fault so I suspect the fault is elsewhere. Check wiring and connectors at back when doing fitting of new element and all seems well.
Your advice to find the fault or doing some testing greatly appreciated.
you would have to ask the shop directly
but a lot of suppliers will not give a warranty unless it is fitted by a manufacturers approved engineer. I have the same problem as any part i fit i have to guarentee and no recourse to the supplier
you will have rights under the sale of goods act to say it must be in good condtion and fit for purpose etc
have you looked at the old switch to make sure its the fault ?