Hob U400 fault codewhat it means and how to fix it
The hob is wired to the wrong supply. It appears within days of installation, and the person to call is the electrician rather than the appliance manufacturer.
Take care
What U400 means
U400 is the code that costs people money for the wrong reason. It means the hob has been connected to a power supply it does not accept, and Lamona and Rangemaster publish the behaviour precisely: the hob has been incorrectly connected, the controls switch off after about one second, the code stays permanently displayed, and on the Lamona a continuous signal sounds. Neff’s wording for the same code is that the hob is not connected properly, disconnect it from the power supply and ensure it has been connected in accordance with the circuit diagram; Rangemaster’s service table calls it wrong connection or overvoltage, 400 V. That is exactly what owners describe — a brand new hob that beeps continuously and dies a second after being switched on.
Because it appears immediately after a kitchen fit rather than after years of use, and because it looks like a fault code on an appliance, the instinct is to ring the manufacturer or book an appliance repair. That is the wrong trade, and it is usually chargeable. The hob is fine. Induction hobs are frequently designed for a particular supply arrangement — a specific voltage, and often a specific configuration of live conductors with links fitted or removed on the terminal block — and getting that wrong is an installation error rather than a manufacturing one.
The person who needs to come back is whoever wired it, and Rangemaster answer the money question in their guides: if there is an installation problem and you do not get the original installer back to fix it, you pay, because service organisations charge for call-outs that correct another installer’s work. Two practical notes. If the hob worked and then started doing this, something has changed on the supply rather than in the hob, which is still an electrician. And this is fixed wiring on a high-current circuit, so it is not a DIY correction whatever a forum tells you.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Hob wired to the wrong supply configuration | The published meaning. Many induction hobs need particular links fitted or removed on the terminal block for a UK single-phase supply. | Common |
| Connected to the wrong voltage | Lamona’s instruction is simply to connect the appliance to the appropriate power supply. | Common |
| Supply changed after the hob was working | Rewiring, a consumer unit change or work on the cooker circuit. Still an electrician rather than an appliance engineer. | Occasional |
What to try yourself
Switch the hob off at the cooker switch on the wall. The continuous tone is the hob telling you not to leave it energised.
Establish when it started. Immediately after installation points squarely at the connection; after years of working points at something that changed on the supply.
Ring whoever wired it rather than the manufacturer. This is an installation fault and it is normally theirs to put right.
Have the model number and the manual to hand. The required connection arrangement is printed in the installation section and it is what the electrician needs.
Do not attempt the connection yourself.
This is fixed wiring on a high-current cooker circuit, live until it is isolated at the consumer unit, and the connection has to match the diagram in the installation instructions. Neff’s remedy is to disconnect the hob and have it connected in accordance with the circuit diagram; Rangemaster’s is to consult your installer or a qualified repair engineer. It is work for a qualified electrician.
Get a qualified appliance engineer to look at your hob
We do not pass enquiries to a repair firm, so there is no form here. When you book a qualified appliance engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0–£150
Time on site
15 minutes
Nothing if the installer comes back to correct their own work, which they normally should. An independent electrician to reconnect it correctly is typically £80 to £150.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related hob fault codes
- HUsually simple to fixThe zone is still hot. Hotpoint and Rangemaster publish the threshold — lit until the glass is below 60 degrees — and Lamona warn it can still burn you after it goes out.Related: same brand
- Pan not detectedUsually simple to fixA zone that flashes and will not heat usually cannot find your pan. Induction needs a ferrous base, big enough for the zone and flat against the glass.Related: same brand
- Zone cut outUsually simple to fixA zone that stops part way through cooking has usually protected itself from overheating. That includes the touch controls, which sit under the glass at the front.Related: same brand
- dEUsually simple to fixDemo mode. The hob lights up, responds to touch and never heats anything, because it is set up for a showroom floor.Related: same brand
Related guides
Common questions about hob U400
The hob is brand new. Is it faulty?
Almost certainly not. U400 reports how the hob has been connected rather than a fault inside it. Booking an appliance repair for this is the commonest expensive mistake in this category, because it is the wrong trade and the visit is usually chargeable.
Why does it beep continuously?
Because it is refusing to operate rather than failing quietly. Lamona publish the sequence: the controls switch off after one second and a continuous signal sounds. The hob is designed to be impossible to ignore in this state.
Can I just change the wiring myself?
No. It is a fixed high-current circuit behind the hob, live until isolated at the consumer unit, and the connection has to match what the manufacturer specifies for your particular model — the terminal links and the supply arrangement in the installation section of your manual. Every manufacturer who publishes this code routes it to the installer or an electrician, and none offers an owner step past switching off.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.