Bosch Induction Hob E4 — Supply Voltage Too Low Fix

What it means

Bosch induction hob E4 means the mains supply voltage has dropped below the safe operating range — typically below 195 V on a 230 V circuit.
The hob disables zones to protect its power electronics from undervoltage damage.
E4 is almost never a hob fault — it's a wiring, breaker, or utility supply issue.

Affected Models

Bosch Series 4/6/8 induction hobs hard-wired to 230 V (EU)
Bosch induction hobs on 208-240 V split-phase (North America)
Bosch combi induction hobs sharing a circuit with other heavy appliances

Common Causes

Another high-draw appliance is on the same circuit (electric oven, kettle, washing machine spinning)
Loose connection at the hob terminal block — most common after a recent installation
Undersized cable run for the distance from the consumer unit
Utility brownout or low supply voltage at the street
Worn breaker or contactor not making solid contact

How to Fix It

Power off and check what else was running.

Switch the hob off at the wall.
Think about what else was on at the moment E4 appeared: oven preheating, dishwasher heating water, electric kettle, tumble dryer.
If two big-draw appliances were both heating, that's enough to pull voltage under the threshold on a marginal circuit.
Measure the voltage at the hob.

If you're comfortable with a multimeter and the hob terminal block is accessible, measure live-to-neutral with the hob switched on but no zones active.
You should see 220-240 V (EU) or 220-240 V across the two hot legs (NA).
Anything under 200 V is the cause and needs an electrician.
Inspect the terminal block.

Most E4 cases trace to a single loose terminal screw at the back of the hob — usually one that worked itself loose during installation or after the first thermal cycles.
Switch off the breaker, open the terminal cover, and check each screw is firmly torqued.
Discolouration around a terminal means it was arcing — that needs full replacement of the block, not just retightening.
Try a single-zone test.

After confirming the wiring is solid, switch the hob back on and run one zone at low power only.
If E4 stays away on a single low-power zone but returns at high power or with multiple zones, the supply circuit can't carry the hob's full load — an electrician needs to either dedicate the circuit or upgrade the cable.

When to Call a Professional

If E4 returns repeatedly and a voltmeter shows the supply is genuinely under 200 V at the hob's terminal block, stop using the hob and call an electrician.
The fix is wiring, not the appliance — and chasing it with the hob still drawing load risks burning the terminal block.

Frequently Asked Questions

Can a low supply voltage damage the hob?

It can, which is exactly why Bosch programs E4 to shut zones off before damage occurs.
Undervoltage forces the hob's switch-mode supplies to draw more current to deliver the same power, which heats components beyond their rated limits.
The shutdown is doing its job — don't bypass it by hammering on the reset and ignoring repeats.