Induction hob not working

What it usually means

Induction works differently enough from every other kind of hob that the diagnosis has to start with the physics. Under each zone is a coil of wire carrying a rapidly alternating current, which creates an alternating magnetic field just above the glass. Put something magnetic in that field and currents are induced inside the metal itself, which heats up because of its own resistance. The hob is not a heater. It is a transmitter, and the pan is the element.

That single fact accounts for the most common complaint, which is a zone that beeps, flashes and refuses to heat. If the pan base is not sufficiently ferrous — aluminium, copper, most glass and much cheap stainless — the hob has nothing to couple to and reports that it cannot find a pan. The test costs nothing: a fridge magnet should stick firmly to the underside of the pan. Two related traps catch people with the right pans. A base much smaller than the zone may not be detected at all, because there is a minimum diameter for each zone, and a base that has warped so it touches the glass only at the rim couples badly and heats slowly or intermittently.

The next question is whether the hob has ever worked properly, because it separates two entirely different situations. Induction hobs are usually built to run on more than one supply arrangement, with links in the terminal block that are set for the installation, and a UK single-phase supply wired without those links in the right places leaves the appliance seeing a supply it will not accept. It then reports a supply or voltage fault, often within days of being fitted, sometimes with half the hob working and half not. Faults that appear at installation are installation faults, and a hob that ran perfectly for five years does not develop one.

Two behaviours look like faults and are documented features. Zones are grouped in pairs sharing an inverter and a share of the total power, so turning one up automatically pulls another down, and the display flashes between two numbers while the hob rebalances. And a zone that switches itself off part way through cooking has usually protected itself from heat — from a pan boiled dry, from the ventilation gap under the hob being blocked by a drawer or a solid batten, or from a self-cleaning oven directly beneath. The electronics live under the glass with the heat, so they have their own limits and their own way of saying so.

That leaves the two genuinely blank cases. A hob with nothing on the display at all is usually not being fed: induction hobs are wired to a cooker circuit rather than plugged in, so check the switch on the wall and the breaker. And a hob that lights up, responds to touch and never heats anything on any zone, with the right pans, is very often in demonstration mode.