On this page
- What is a granny charger and how should it behave?
- What do the control box lights and reset button mean?
- Has the RCD in the plug tripped?
- Is it plugged into the right kind of socket?
- Is the socket worn or hot? When to stop
- Could the granny charger itself be faulty?
- Symptom, likely cause and what to do
- What else could be stopping it?
- Frequently asked questions
If your granny charger has stopped working, start with the simplest causes before you assume the lead is faulty: check the status lights and reset button on the in-cable control box, make sure it is plugged into a sound, dedicated 13A socket, and see whether the small RCD in the plug has tripped. A portable charger that will not come back to life, or a socket that feels hot, may need replacing, so it is worth knowing what to look for before you buy a new portable EV charger. Work through the checks below in order, and stop at once if anything is hot, discoloured, or smells of burning.
What is a granny charger and how should it behave?
A granny charger is the portable lead that plugs into a normal 3-pin domestic socket at one end and your car at the other. The chunky box part way along the cable is the in-cable control box, often shortened to ICCB. It manages the charge and carries the safety electronics.
Granny charging is slow by design, usually around 2.3kW, so a full charge can take a long time. If your only complaint is that it feels slow, that is probably normal rather than a fault. We cover this in more detail in why is my EV charging slowly.
When it is working correctly you should see steady status lights and the car should report that it is charging. If nothing lights up, or the lights show a fault pattern, run through the checks below.
What do the control box lights and reset button mean?
Most in-cable control boxes have a row of status lights and, on many units, a reset button. Broadly speaking, a steady light usually means power and a normal state, while a flashing or coloured warning light usually points to a fault the box has detected and paused for.
Light patterns vary between brands, so check the little guide printed on the box or in the instructions that came with it rather than guessing. We are not going to invent specific codes here, because the wrong interpretation could send you down the wrong path.
If the box has a reset button, you can press it once to clear a one-off glitch. If the same fault returns straight away, treat that as the charger telling you something is genuinely wrong, and move on to the socket and RCD checks rather than resetting over and over.
Has the RCD in the plug tripped?
Many granny chargers have a small RCD or test and reset function built into the plug or control box. If it has tripped, the charger will not deliver power until it is reset.
It is fine to reset it once. If it trips again as soon as you start charging, stop. A repeated trip is a sign of a real fault in the cable, the socket, or the wiring, and that is a job for a qualified electrician or the charger manufacturer, not something to keep resetting.
Do not defeat, bypass, or tape over any safety device. It is there to protect you.
Is it plugged into the right kind of socket?
A granny charger draws a steady, heavy current for hours, so it needs a sound, dedicated 13A socket on its own. The socket should be in good condition and not shared at the same time with anything else that pulls a big load.
- No extension leads: plug the charger straight into the wall socket, not into an extension or reel.
- No multi-way adaptors: do not run it through a four-way block or a double adaptor.
- No sharing with big appliances: avoid a socket on the same spur as a kettle, washing machine, tumble dryer, or heater running at the same time.
Using the wrong kind of socket can cause the charger to stop, trip, or run hot. If you are unsure whether a socket is suitable for repeated long charges, ask an electrician to check it.
Is the socket worn or hot? When to stop
A granny charger lead that runs mildly warm under load is normal. A socket or plug that is hot to the touch, discoloured, scorched, or smells of burning is not. That is a warning sign.
If you notice any of this, stop charging immediately, switch off and unplug at the source, and stop using that socket and cable until they have been checked. Do not try to repair a damaged plug, socket, or cable. We go into the warmth question in more depth in EV charging cable getting hot.
A tired socket that gets hot often means a loose or worn connection, which an electrician should look at. If the fault is in the cable itself and the lead is damaged, replace it rather than risk it.
Could the granny charger itself be faulty?
If the socket is sound, the RCD holds, and the control box still will not work, the charger may have failed. Portable chargers take a lot of heat cycles and knocks over their life, and the control box electronics can give up.
A faulty granny charger is not something to bodge back together. If it is out of warranty and clearly not working, the safe answer is to replace it with a new portable EV charger. If it is under warranty, contact the manufacturer first.
If you are weighing up whether a portable charger is still the right long-term option for you, it is worth reading granny charger vs wallbox before you spend.
Symptom, likely cause and what to do
| Symptom | Likely cause | What to do |
|---|---|---|
| No lights on the control box at all | No power at the socket, or the charger has failed | Check the socket works, check the consumer unit, then suspect the charger if the socket is fine |
| Warning or flashing light on the box | The box has detected a fault and paused | Check the box's own light guide, press reset once, stop if the fault returns |
| RCD in the plug has tripped | A one-off glitch, or a real fault in cable, socket or wiring | Reset once; if it re-trips, stop and call an electrician or the manufacturer |
| Charging but very slow | Granny charging is around 2.3kW by design | This is usually normal; see the slow charging guide |
| Socket or plug hot, discoloured or smells of burning | Worn socket, loose connection or damaged cable | Stop now, unplug at the source, stop using it, get it checked |
| Nothing works on an extension or multi-way | Wrong kind of socket for a long, heavy load | Move to a dedicated 13A wall socket in good condition |
What else could be stopping it?
Not every charging problem is the granny charger. If power at the socket looks fine and the car still will not take a charge, the cause may be at the car end, such as a charge flap not released, a schedule holding it, or a fault on the car. Our guide on when the EV wont charge at home walks through those causes.
If any of the terms here are unfamiliar, the EV charging glossary explains ICCB, RCD, 13A sockets and the rest in plain English. You can also browse all our help in the EV charging guides.
Quick tool: a granny charger is slow by design. Our EV charging time calculator shows how long a top-up takes on a 3-pin plug versus a wallbox.
Frequently asked questions
Why has my granny charger stopped working?
The common causes are a tripped RCD in the plug, a worn or shared socket, a fault the control box has paused for, or the charger itself failing. Work through the socket and RCD checks first, and stop if anything is hot or smells of burning.
Can I reset my granny charger?
Yes, if the control box has a reset button you can press it once to clear a one-off glitch, and you can reset a tripped RCD in the plug once. If the fault or trip returns straight away, stop and treat it as a real fault for an electrician or the manufacturer.
Can I use my granny charger with an extension lead?
No. A granny charger draws a heavy current for hours and should go straight into a sound, dedicated 13A wall socket. Extension leads, reels, and multi-way adaptors can overheat and are not suitable.
Why is my granny charger so slow?
Granny chargers run at around 2.3kW by design, which is much slower than a wallbox, so a slow charge is usually normal rather than a fault. If you need faster home charging, a wallbox is the usual step up.
The socket feels hot when I charge, is that a problem?
A cable running mildly warm is normal, but a socket or plug that is hot, discoloured, or smells of burning is a warning sign. Stop charging, unplug at the source, stop using that socket, and have it checked by an electrician.
Do I need to replace my granny charger or can it be repaired?
If the socket is sound and the RCD holds but the charger still will not work, it has likely failed. Do not try to repair a damaged charger or cable; contact the manufacturer if it is under warranty, or replace it with a new portable EV charger.
Written by
Gavin RogersCo-founder · drives a BMW iX2
Gavin runs a BMW iX2 and spends a lot of his time on the gap between a car's headline charging figure and what you actually get at home. A car quoting 11kW three-phase still charges at 7.4kW on a normal single-phase UK house, and that is exactly the kind of thing the site exists to make clear.
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