The electronic ignition spark stays on constantly — why?

There could be water near the ignition knob, perhaps from cleaning with an overly wet sponge, causing a false contact.

Our advice is to remove the knobs (they are press-fitted) and blow warm air over the area (a hairdryer works well), then wait for it to dry completely.

If the problem persists after this, unplug the hob and leave the appliance off for at least a day.

However, if even that does not resolve the issue, the problem could be a switch that is mechanically stuck (which means the hob needs dismantling) or the control unit.