Short answer: Most iPhone problems come down to five causes — a degraded battery, full storage, an outdated iOS version, a damaged or non-genuine part, or heat. Working through those in order resolves the majority of complaints without a service visit. The exceptions worth taking seriously are Face ID failure, liquid exposure and anything involving swelling.
The phone feels slow
The most common complaint, and usually not the processor.
Once battery capacity drops below roughly 80 per cent, iOS may limit peak performance to prevent unexpected shutdowns. That throttling is what people experience as an old phone getting slow. Check Settings → Battery → Battery Health & Charging first — see what the number means.
The second cause is storage. A phone running above roughly 90 per cent full slows measurably and cannot install updates. Check Settings → General → iPhone Storage. See the storage guide.
Restarting properly — a full power off, not just a lock — also clears a surprising amount.
The battery drains quickly
Check battery health first. If it reads well, look at Settings → Battery for which apps consumed power over the last day and ten days. A single misbehaving app is often the culprit.
Other usual suspects: 5G in a weak-signal area (try 5G Auto rather than 5G On), background app refresh, and location services set to Always rather than While Using.
Heat is the underrated one. A phone that gets hot regularly — on a dashboard, in direct sun, charging under a pillow — loses capacity faster and permanently.
It will not charge
Work through in this order.
Try a different cable and adapter. Cables fail internally far more often than ports do.
Look inside the port with a torch. Lint compacts at the bottom over years and prevents the connector seating fully. Clean gently with something non-metallic, with the phone powered off. Green or white residue means corrosion, which is liquid damage — see IP68 explained.
Check for a liquid warning. If iOS says liquid has been detected, do not override it and charge anyway. That causes more damage than the water did.
Force restart if the screen is unresponsive: volume up, volume down, then hold the side button until the Apple logo appears.
Face ID has stopped working
Take this one seriously, because it is rarely a software issue.
Try the obvious first — clean the notch or Dynamic Island area, remove any case obstructing it, and reset Face ID under Settings. Add an alternate appearance if you wear glasses.
If it cannot be set up at all, or the option is greyed out, the module has been damaged or replaced. Face ID components are cryptographically paired to the device and cannot be transplanted from another iPhone, which means a non-genuine repair permanently disables it. This is also why Face ID enrolment is a standard check when buying a used device — see the 9-step checklist.
The phone gets hot
Some warmth during charging, gaming, navigation or a long video call is normal. Concerning is heat while idle, or heat severe enough to trigger a temperature warning.
Remove the case while charging, avoid using it in direct sun, and close navigation when you are not driving. If a specific app causes it consistently, update or remove that app.
Persistent heat while idle after a restart is worth having inspected.
Wi-Fi or mobile data keeps dropping
Toggle airplane mode on and off first. Then Settings → General → Transfer or Reset iPhone → Reset → Reset Network Settings — this clears saved Wi-Fi passwords, so have them to hand.
On dual-SIM devices, check whether the problem affects both lines or one. A single failing line usually points to the SIM or the operator rather than the phone.
Stop using it immediately if
Three situations are not troubleshooting problems.
The screen or back is lifting, or the phone will not sit flat. That indicates a swelling battery. Stop charging, power it off, and take it to a service centre. A swollen lithium battery is a genuine safety risk, not an inconvenience.
It got wet and now behaves oddly. Corrosion continues invisibly.
It becomes too hot to hold comfortably. Power it off and let it cool before doing anything else.
When the fix is not worth it
If a repair quote approaches half of what the phone is currently worth, or the device is close to losing iOS support, the money is usually better spent elsewhere. The framework is in repair or replace.
If you do replace it, the renewed range starts well below new pricing, with 100% battery health, over 300 quality checks and an 18-month warranty on iPhones.
Frequently asked questions
Why is my iPhone slow?
Usually a degraded battery or full storage rather than the processor. Below roughly 80 per cent battery capacity, iOS may limit peak performance, and a phone above 90 per cent full slows measurably.
Why is my iPhone battery draining so fast?
Check battery health first, then the per-app breakdown in Settings, Battery. Weak-signal 5G, background app refresh and always-on location are common causes. Regular overheating permanently reduces capacity.
Why won't my iPhone charge?
Try another cable and adapter, then check the port for compacted lint with a torch. Corrosion in the port indicates liquid damage. Never override a liquid-detected warning to charge.
Why has Face ID stopped working?
Clean the sensor area and reset Face ID in Settings. If it cannot be enrolled at all, the module has likely been damaged or replaced, since Face ID components are paired to the device and cannot be transferred.
Is a swollen iPhone battery dangerous?
Yes. If the screen or back is lifting, stop charging, power the device off and take it to a service centre. A swollen lithium battery is a safety hazard.
Does putting a wet phone in rice work?
No. Apple advises against it. Rice pushes starch and dust into the ports without meaningfully speeding drying.
