Smeg E5 fault codewhat it means and how to fix it
The hob has judged the mains voltage signal invalid. Smeg say to check the supply voltage, which on a hardwired cooker is an electrician’s job rather than yours.
Take care
When does the code appear?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
When does the code appear?
A transient. The electronics saw a supply they could not lock on to for a moment and stopped rather than running on it, which is the protection behaving correctly.
Restart it once and note the date. If months pass without a repeat, nothing further is needed.
When does the code appear?
That timing points at voltage drop rather than at the appliance. The hob is accurately reporting a supply that sags when the house asks a lot of it.
This is an electrician’s question about the circuit and the cable feeding the cooker, not an appliance repair.
When does the code appear?
A consistent invalid signal with no load to explain it is the branch where Smeg’s own escalation applies, and the fault may be in the hob’s own supply detection rather than in the supply.
Have the supply confirmed as sound first, then book a service visit. Doing it in that order avoids paying for a diagnosis of the wrong appliance.
What E5 means
Smeg publish E5 as an invalid main voltage signal, with the instruction to check the supply voltage and the note that an engineer will be needed if the error persists. The word doing the work in that sentence is "signal". The hob is not reporting that your house has no electricity, which would be obvious without a code. It is reporting that the mains waveform arriving at its electronics is not one it can work with, which is a narrower and more interesting claim.
Induction electronics synchronise their switching to the incoming supply, so they need voltage within a defined band and a clean, regular waveform to lock on to. Anything that distorts that reads as an invalid signal. It is worth separating this from U400, which sits in the same cluster and is often confused with it. U400 says the appliance has been connected wrongly, and it turns up on new installations. E5 says the appliance is connected in a way it accepts but the electricity coming down that connection is not what it expects, and it can turn up at any point in a cooker’s life. One is about the wiring at the terminal block, the other about what is travelling through it. That distinction is what decides whether you ring the installer or an electrician. The practical difficulty with "check the supply voltage" is that Smeg do not say who checks it, and measuring the voltage at a cooker connection means opening a live high current connection, which is not householder work. What you can gather without touching anything is evidence, and it is genuinely useful evidence.
Note whether the code coincides with something else in the house starting, such as a shower or an immersion heater, which points at voltage drop on a shared or undersized circuit. Note whether lights dim or other appliances misbehave at the same time, which widens the problem beyond the cooker. Check the isolator, and specifically the omnipolar switch upstream of the appliance that Smeg mention in their own troubleshooting for a dead display, because a switch that is partly made can produce a supply the hob will not accept. A single E5 after a power cut or a flicker is a transient worth one restart. A recurring one is the hob telling you something accurate about its circuit, and resetting past that is arguing with the messenger.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Voltage drop when another heavy load starts | A shower, immersion heater or kiln pulling hard on the same supply drags the voltage down briefly, and the hob refuses the moment it falls outside its band. | Common |
| A partly made connection or isolator | Smeg point at the omnipolar switch upstream of the appliance in their own troubleshooting. A switch or terminal that is not fully made distorts what reaches the electronics. | Common |
| A transient after a power cut or flicker | The benign case. The electronics saw one bad cycle, declined to run on it and reported the fact, and a single restart is the whole of the answer. | Common |
| An undersized or very long supply cable | The voltage measured at the cooker falls as it draws current, so the code appears when the appliance is working hardest rather than at random. | Occasional |
| A supply problem outside the property | Rarer, and it usually shows itself elsewhere in the house first. Worth mentioning to an electrician rather than assuming, since they can raise it with the network operator. | Rare |
What to try yourself
Switch the cooker off at its wall switch, wait a moment and switch it back on once, to clear a transient.
Check the omnipolar switch or isolator upstream of the cooker is fully in the on position, which Smeg raise themselves for supply symptoms.
Watch for what else is running when the code appears. A shower or immersion heater starting at the same moment is a strong clue.
Note whether the code favours heavy use of the hob rather than appearing from cold, since that separates voltage drop from a supply fault.
Note whether lights dim or other appliances stumble at the same time, because that takes the problem beyond the cooker.
If it recurs, book an electrician rather than an appliance engineer, and hand over what you have noticed about the timing.
Do not attempt to measure the voltage at the cooker connection or the terminal block. That is a live high current connection and testing it is work for someone qualified with the right instrument.
Get a qualified appliance engineer to look at your Smeg E5
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–£250
Time on site
1 hour
Nothing for a transient after a power cut. An electrician’s visit to trace and remake a poor connection, and more if the cooker circuit or cable needs upgrading.
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 Smeg fault codes
- U400Get it checkedSmeg publish six words for this: wrong connection, connect the equipment properly. On a hardwired range cooker that means an electrician rather than anything you can do.Related: supply and connection
- SHOUsually simple to fixNot a fault at all. The oven is in showroom mode, so the control panel works and no heating is possible. Smeg publish how to switch it off.Related: same brand
- E2Get it checkedOverheating of the inductor on the hob, but E2 is also in Smeg’s pyrolytic oven list. Which display it is on changes the answer completely.Related: same brand
- Er03Usually simple to fixA knob or button is being read as held on. On these knob-operated range cookers that usually means a knob kept turned to A too long. Release it, then clean the hob as Smeg say.Related: same brand
- E6Get it checkedPower failure to the power board. Smeg publish a timed remedy rather than a flick of the switch: turn the appliance off for a full five minutes.Related: same brand
- EAGet it checkedA power circuit board error on the induction hob. Rangemaster publish an EA too, describing something different, so check which brand’s table you are reading.Related: same brand
Own a Smeg range cooker? Save it and its codes come first next time.
Related guides
Common questions about Smeg E5
What is the difference between this and U400?
U400 is Smeg saying the appliance has been connected wrongly, and it almost always shows up on a new or recently reconnected cooker. E5 is the appliance saying the connection is acceptable but the electricity arriving through it is not a signal it can use. The first is a question for whoever wired it; the second is a question about the circuit and the supply.
Should I call an electrician or an appliance engineer?
For a recurring E5, an electrician first. The hob is reporting on the supply feeding it, and the likely causes are a partly made connection, an undersized cable or a circuit that sags under load, all of which sit outside the appliance. Smeg do say an engineer is needed if the error persists, and that is the right next step once the supply has been shown to be sound.
The display went completely blank instead of showing a code.
That is a different symptom with its own published answer. Smeg’s troubleshooting for a completely dead display is to check the mains power supply and to check that the omnipolar switch upstream of the appliance supply line is in the on position. A blank display means nothing is arriving; E5 means something is arriving and the hob does not like it.
Can an invalid supply damage the cooker?
The code exists so that it does not. The hob stopping is it declining to switch its power electronics against a waveform it cannot synchronise with. The risk lies in overriding that repeatedly to keep cooking, and in the underlying cause: a connection that is only partly made carries the full cooker current through a poor joint, and poor joints get hot.
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 support portal
- 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.