Smeg ERR4 fault codewhat it means and how to fix it
The pyrolytic door lock has not attached to the door, often because the door was opened while it was locking. Smeg publish a real owner remedy.
Take care
What is the oven doing now?
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.
What is the oven doing now?
This is the case Smeg describe. The lock did not confirm, so the oven abandoned the cycle before heating rather than running one behind an unlocked door.
Switch off and on, wait a few minutes, check the door closes cleanly, then start again and leave the door alone.
What is the oven doing now?
That is not a fault at all. Smeg publish that a safety device prevents functions being selected while the door lock is still active, because the cavity remains too hot for cooking.
Leave it to cool and try again later. Nothing needs resetting and nothing needs booking.
What is the oven doing now?
Smeg’s published cause does not fit, so the mechanism or the switch that confirms it is the likelier explanation and the published remedy has been exhausted.
Note the error message, the function and the set temperature, and contact technical support, which is Smeg’s own instruction for oven error messages.
What ERR4 means
ERR4 is the most useful code Smeg publish for the oven side of a range cooker, and it comes from the troubleshooting table in the manual rather than from either of their help portal articles. Their text is worth having in full: the door lock has not properly attached to the door, this might be because the door was accidentally opened during the door lock activation, and the remedy is to switch the appliance off and on again, waiting a few minutes before selecting a new cleaning cycle. A cause and a cure, in a category where most manufacturers publish neither. The mechanism behind it explains why the timing matters. A pyrolytic cleaning cycle takes the cavity to a temperature far above any cooking setting in order to burn residue to ash, and the door has to be locked shut before that starts.
There is a short window at the beginning of the cycle when the lock is driving across, and if the door moves during that window the mechanism does not engage as it should. The oven detects that it cannot confirm a locked door, abandons the sequence and reports ERR4, which is the appliance refusing to heat a cavity to several hundred degrees behind a door it is not certain about. Smeg’s two instructions, switching off and on and then waiting a few minutes, both make sense in that light. Powering down lets the control clear its state and re-run the lock sequence from the beginning, and the wait gives the mechanism time to return to a defined position rather than being commanded again mid-travel. It is also worth knowing the related behaviour on the same page, because owners often mistake it for a fault.
After a pyrolytic cycle, Smeg publish that you may find no function can be selected until the door lock has deactivated, and they explain it plainly: the appliance has a safety device that prevents functions being selected while the door lock is active, because the cavity is still too hot for any kind of cooking. That is a locked, hot oven behaving exactly as designed. If ERR4 comes back on a door that has not been touched during the cycle, the mechanism or its switch is the more likely explanation, and Smeg’s closing instruction for oven error messages applies: note down the error message, the function and the set temperature, and contact technical support.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| The door was moved as the lock engaged | Smeg’s own stated cause. The lock drives across during a short window at the start of the cycle, and a nudge in that window stops it seating. | Common |
| The door is not quite closed | A shelf, a tray or a roasting dish left proud of the runners holds the door a few millimetres open, which is enough to stop the lock confirming. | Common |
| A cycle started again too soon | Smeg specify waiting a few minutes before selecting a new cleaning cycle, and commanding the lock again while it is still mid-travel repeats the failure. | Occasional |
| A worn lock mechanism or its switch | Where a repeating ERR4 on an undisturbed door points. The mechanism has to work at pyrolytic temperatures, and its confirming switch is part of the assembly. | Occasional |
| Hinges or a seal that have moved | A door sitting a little differently after years of use, or a displaced seal, changes where the lock has to reach to engage properly. | Rare |
What to try yourself
Do not try to force the door. If the cycle has already been running, the cavity may still be extremely hot behind a lock that has not released.
Switch the appliance off and on again, which is the first half of Smeg’s published remedy for this code.
Wait a few minutes before selecting a new cleaning cycle. Smeg specify the wait, and starting straight away tends to repeat the failure.
Check the door closes fully and squarely, and that nothing inside the cavity is holding it proud of the seal.
Start the cycle and then leave the door alone. The lock engages in the first moments, which is the window Smeg identify.
If it returns on a door you have not touched, note the message, the function and the set temperature, and contact technical support as Smeg instruct.
Never attempt to release a pyrolytic door lock by hand or with a tool. The lock is holding a cavity that reaches several hundred degrees, and defeating it while it is hot is how people get burned.
Get a qualified appliance engineer to look at your Smeg ERR4
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–£240
Time on site
20 minutes
Nothing when the published remedy works, which is the common case. A service visit and a door lock assembly if the code returns on a door that was never disturbed.
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
- 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: controls and lockouts
- 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
- 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: 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
- 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
- E5Get it checkedThe 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.Related: same brand
Own a Smeg range cooker? Save it and its codes come first next time.
Related guides
Common questions about Smeg ERR4
Can I still use the oven for ordinary cooking?
Usually yes, once the code has cleared and the lock has released, because the fault is in confirming the lock for a cleaning cycle rather than in the oven heating. Do not use it while the door is still locked from an abandoned cycle, and do not attempt another pyrolytic clean until the code stops appearing.
Why does opening the door matter so much?
Because the lock engages in a short window at the very start of the cycle. Smeg say the code may be caused by the door being accidentally opened during door lock activation, and if the mechanism is interrupted mid-travel it cannot seat. The oven then has no confirmation that the door is locked, and it will not take the cavity to pyrolytic temperature on an assumption.
The oven will not let me select anything after a clean. Is that ERR4 as well?
No, and Smeg publish it separately as normal behaviour. A safety device prevents any function being selected while the door lock is active, because the cavity is still too hot to cook in. Wait for it to cool and the controls come back. There is no code and nothing to fix.
Why is ERR4 not on Smeg’s help portal code lists?
It is in the manual instead, in the troubleshooting table, which is why it is easy to miss. Their portal carries an induction list and a pyrolytic oven list, and ERR4 is on neither. It is still Smeg’s own published text, and it is better documented than most of what they publish: it has a stated cause and a stated remedy, which the pyrolytic codes do not.
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.