What does the U400 error mean on an induction cooktop?#
U400 means the cooktop has detected that it is connected to the wrong mains supply — a wiring or connection error made when the unit was installed or reconnected. It is an installation code, not a cookware or heat message, so it points squarely at how the appliance is wired. Because it almost always appears right after installation or a supply change, the first thing to notice is timing: if U400 showed up the moment the cooktop was first powered on, the connection is the prime suspect. U400 is documented on Bosch, Siemens and Neff (BSH) induction cooktops. As the causes below make clear, this is an electrical-connection problem, so the safe path leads to whoever wired it — a qualified installer or a licensed electrician — rather than to a homeowner reset.
U400 on an induction cooktop: what it means and what to check#
An induction cooktop shows U400 when the appliance is connected to the wrong mains supply — a wiring or connection error at install.
| Likely cause | What's happening | How likely | First thing to check | Fix it yourself? |
|---|---|---|---|---|
| Two-phase supply wired as a single bridged phase | the supply is bridged wrongly, so the board sees the wrong configuration | Most likely | have an electrician re-check against the wiring diagram | Pro repair |
| Bridging clips left in place on a split supply | clips for one supply type present the wrong wiring to the terminal | Possible | confirm the bridge clips match the supply type | Pro repair |
| Incorrect voltage supply at the terminal | the terminal voltage does not match the required connection | Less likely | book an electrician to verify the supply configuration | Pro repair |
| Fastest thing to try first: Have an electrician re-check against the wiring diagram. | ||||
| If U400 keeps returning: Clips for one supply type present the wrong wiring to the terminal — confirm the bridge clips match the supply type. |
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How to clear the U400 error yourself#
The safe home role with U400 is to observe and then hand it to a qualified person, because every cause involves the fixed wiring at the terminal block — and that is not homeowner territory. Do not open the terminal block or attempt to rewire anything. What you can safely note is the context that tells the electrician where to look. Many induction cooktops can be wired for different supply arrangements, and U400 typically means the phases have been connected the wrong way: a supply that should be split across separate legs wired as a single bridged phase, or the small bridging clips that configure the terminal block left in place (or removed) incorrectly for your supply. An incorrect voltage presented at the terminal because of that mis-configuration is what the cooktop is objecting to. Pass those observations — recent install, wrong-looking connection, code from first power-up — to a qualified installer or licensed electrician, who will compare the wiring to the appliance’s connection diagram and correct it. U400 clears once the supply is wired as the cooktop expects.
When the U400 error needs a technician#
U400 leaves very little for the owner to do beyond recognising that it is a wiring fault and calling the right person. The causes — phases bridged instead of split, bridging clips wrong for the supply, or an incorrect voltage at the terminal from a mis-configuration — are all in the fixed electrical connection, and correcting them means working at the terminal block against the appliance’s wiring diagram. That is qualified-installer or licensed-electrician work; it must be done safely and to code. An appliance technician is only relevant afterwards, in the rare case that the wiring is confirmed correct to the diagram and U400 still appears, which would then point at the cooktop’s own supply-sensing.
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Induction cooktop U400 error: frequently asked questions#
What does the U400 error mean on an induction cooktop?#
U400 means the cooktop is connected to the wrong mains supply — a wiring or connection error at installation. It is an install-time fault rather than a cookware or heat message, and it typically appears the first time the unit is powered up after being wired or reconnected.
Can two-phase supply wired as a single bridged phase trigger the U400 error?#
Yes, that is the classic cause. If a supply that should be split across separate legs is wired as a single bridged phase, the cooktop sees the wrong supply arrangement and reports U400. Correcting the connection to match the appliance’s wiring diagram is a job for a qualified installer or electrician.
Does bridging clips left in place on a split supply cause the U400 code on an induction cooktop?#
It can. The small bridging clips in the terminal block configure the cooktop for a particular supply, and if they are left in place — or removed — incorrectly for your wiring, the unit sees the wrong voltage arrangement and shows U400. Setting the clips correctly is electrical work for a qualified person.
Should I check for incorrect voltage supply at the terminal first?#
Check it as a cause, but do not open the terminal yourself. An incorrect voltage presented at the terminal because of a mis-configured connection is exactly what U400 reports. A licensed electrician should measure the supply at the terminal and correct the wiring against the connection diagram.
Can I clear the U400 error myself?#
No — U400 is not a homeowner reset. Because it reports a wiring error in the fixed supply, it clears only once the connection is corrected to the appliance’s diagram. Attempting to run the cooktop without fixing the wiring is unsafe; call a qualified installer or electrician.
Is it safe to keep cooking when U400 shows?#
The cooktop has refused to operate, which is its way of protecting itself and you from a wrong supply, so it is not running in a hazardous state. But it should not be used until the connection is corrected — leaving a mis-wired supply in place is the real risk, so have it put right before cooking.
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