Wolf Legacy Induction Code U400: Over voltage

What U400 means

On Wolf legacy induction ranges built before 2018, such as the IR304TE/S/TH and IR365TE/S/TH, code U400 means over voltage. The cooktop is seeing more voltage than it is designed to handle, so it shuts the zones down to protect its electronics. Owners see U400 after a surge, during utility problems, or when the supply to the range is unstable. The display holds U400 until the voltage settles.

Common causes of U400

Supply voltage at the range above the acceptable level
Loose or high-resistance connection that causes voltage swings
Utility or house wiring condition
Power input electronics reporting the reading incorrectly

✓ One safe check you can try

1. Turn all zones off. 2. Check the breaker and reset it fully if it has tripped. 3. Wait several minutes, then try a low heat. 4. If U400 comes back, stop using the range, and do not open it or probe the power connection. Call us so we can measure the supply safely.

! Why to stop there

Over voltage can damage the cooktop electronics
The cause may be outside the range, in the house supply
We check the supply and the cooktop before suggesting a fix
Our price is written before work starts, with a 30-day warranty

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Range codes

0121Wolf Dual Fuel DFxx50 Code 0121: Right convection drive shorted in the right oven E01Wolf IR30450 and IR36550 Induction Range Code E01: Left Key Error 0122Wolf Dual Fuel DFxx50 Code 0122: Right convection drive shorted in the left oven ErrWolf Legacy Dual Fuel Range Code Err: How the Error Display Works 0221Wolf Dual Fuel DFxx50 Code 0221: Bake element DLB relay shorted, right or single oven Ignition LockoutWolf Gas Burner Code Ignition Lockout: Slow-Blinking Call-for-Heat Light 0222Wolf Dual Fuel DFxx50 Code 0222: Bake element DLB relay shorted, left oven LOWER RELAYWolf Legacy Dual Fuel Range Message LOWER RELAY: Shift Register Feedback Failure

U400U400 questions

Can a power surge cause U400?

Yes. A surge or a spike from the utility can push the supply above what the cooktop accepts. The range shuts down on purpose to protect itself.

Do I need an electrician or a Wolf technician?

Start with us. We measure the supply at the range and tell you whether the problem is in the cooktop or in the house wiring, so you only call an electrician if needed.

Is it safe to retry cooking after U400?

One careful retry after a breaker reset is fine. If U400 repeats, stop, because running on high voltage can harm the electronics and the problem needs measuring.