A Windows 11 PC running hot — fans constantly at full speed, the chassis warm to the touch, performance throttling during normal tasks — usually traces back to one of three things: a stuck background process pegging the CPU, accumulated dust restricting airflow, or thermal paste that’s degraded after years of use. Most cases are software-fixable in under 20 minutes. We go deeper on the whole subject in our Complete Guide to Fixing Windows, Browser, and Software Errors.
The single fastest diagnostic: Ctrl+Shift+Esc → Task Manager → Performance tab → CPU. If it’s sitting at 60-100% with nothing visibly running, you have a runaway process. If it’s at 10-20% but temps are still high, the issue is cooling, not load. This one observation tells you which half of this guide to focus on.
Identify what’s actually using the CPU
In most cases this is the answer. Open Task Manager → Processes tab → click “CPU” column to sort by usage. The top entry is your culprit. Common surprises:
- Microsoft Compatibility Telemetry (CompatTelRunner.exe) — pegs CPU for hours after major updates while it inventories your system
- Windows Search Indexer (SearchIndexer.exe) — rebuilds the search index periodically, especially after adding lots of files
- Antivirus full scan — sometimes runs in the background unannounced
- Service Host: Local System — vague label hiding things like Windows Update Service
- Cryptocurrency miners — uncommon but real; check for processes you don’t recognise running consistently at high CPU
Right-click the offending process → End task. If it’s a legitimate Windows process that comes back: it’s doing necessary work. Let it finish. CompatTelRunner especially can take 2-4 hours after an update; it’s not stuck, it’s working.
Check actual temperatures, not just symptoms
“PC running hot” is subjective. Get real numbers. Download HWMonitor or Core Temp (both free) → run for 5 minutes → check the max temperatures recorded:
| CPU temp | What it means |
| 40-60°C idle / 60-75°C load | Normal — no issue |
| 70-85°C under sustained load | Warm but acceptable for most chips |
| 85-95°C sustained | Too hot — thermal throttling likely |
| 95°C+ or thermal shutdown | Critical — fix immediately |
Below 80°C under load = software fix. Consistently above 85°C = cooling problem regardless of what software does.
Quick power and performance adjustments
Settings → System → Power & battery → Power mode → switch to “Balanced” (not “Best performance”). High-performance mode keeps the CPU at max clock even when idle, generating unnecessary heat. The performance difference for everyday tasks is barely noticeable.
If you’re on a laptop, there’s another setting worth checking: Control Panel → Power Options → active plan → “Change advanced power settings” → Processor power management → “Maximum processor state” → set to 99% (not 100%). This single percentage point disables Intel Turbo Boost / AMD Boost, which dramatically reduces peak temps with minimal real-world performance loss. Old trick, still works.
Clean the dust — yes, really
If the machine is more than a year old and you’ve never opened it: this is probably the issue. Dust accumulates inside the heatsink fins and chokes airflow. The fan spins faster to compensate, you hear it, the temps stay high anyway.
For desktops: shut down, unplug, open the side panel, use compressed air (held upright, never inverted) to blow out the CPU heatsink, GPU heatsink, case fans, and PSU vents. Hold fan blades still while spraying so you don’t over-spin them. Takes 15 minutes.
For laptops: this is harder. Bottom panel removal varies by model. If you’re not comfortable opening it, compressed air through the existing exhaust vents helps somewhat but won’t reach the heatsink. A proper cleaning at a repair shop runs £30-£60 and is worth it on a laptop more than 2-3 years old.
Background apps and startup overhead
Settings → Apps → Startup → disable everything except antivirus and essential drivers. Especially: Discord, Steam, Epic, Spotify, OneDrive, Adobe Creative Cloud, gaming launchers, and overlay apps (NVIDIA GeForce Experience, Razer Cortex). These all run continuously when you log in, idle-consuming CPU cycles.
Also disable Settings → Privacy and security → General → “Let apps show me personalized ads” and related telemetry. They run background processes that add small but constant CPU load.
Our guide on high CPU usage diagnosis goes deeper on identifying specific runaway processes, and our Windows freezing guide covers the related symptoms when overheating reaches thermal throttling. For deep cooling solutions including thermal paste replacement and aftermarket cooler installation, Intel’s processor documentation covers operating temperature ranges and cooling requirements for specific CPU families.
Thermal paste — the unsung hero
This is the one most people miss. The thermal paste between your CPU and its heatsink dries out over 3-5 years. When it does, heat transfer efficiency drops dramatically — even a perfectly clean machine will run hot. Symptoms: temperatures gradually creep higher over months without any obvious cause; fans run louder than they used to; sustained load triggers throttling.
Replacing thermal paste is a 20-minute job for someone comfortable with PCs. For laptops it’s significantly more involved — often requiring complete disassembly. If your machine is 3+ years old and runs hot despite a clean heatsink: this is almost certainly your fix. A tube of decent paste (Arctic MX-4, Noctua NT-H1, Thermal Grizzly Kryonaut) costs £5-£10 and lasts dozens of applications.
Quick reminder: Don’t go overboard with the amount. A pea-sized blob in the centre of the CPU IHS is enough. Spreading it manually causes air bubbles; the heatsink pressure spreads it correctly.
GPU contribution to overall heat
Sometimes the CPU isn’t the problem at all — the GPU is. A hot GPU dumps heat into the case, which the CPU cooler then has to deal with. Check GPU temps in HWMonitor too. If GPU is sitting at 80-90°C while gaming or doing GPU-accelerated work: the GPU needs cleaning, repasting, or its fans may be failing.
Browser GPU acceleration is also worth checking. Chrome and Firefox both have hardware acceleration enabled by default, which is normally good, but with some buggy GPU drivers it can cause the GPU to run at high clocks even on simple websites. Chrome Settings → System → “Use hardware acceleration when available” → toggle off as a quick test → see if temps drop. If yes, update the GPU driver and turn acceleration back on.
Fan curves and BIOS settings
Most motherboards default to conservative fan curves — fans don’t ramp up until the CPU is already at 70°C or higher. The CPU spends time at uncomfortable temperatures while the fans are still spinning slowly.
Reboot → enter BIOS (F2 or Delete during POST) → look for “Fan Control” or “Q-Fan Control” or “Smart Fan Mode” → adjust the curve so fans start ramping at 50-55°C instead of 70°C. Trade-off: slightly louder under load, but the CPU stays measurably cooler. Most users gladly accept this. Save changes, reboot, test under load.
Same idea applies in laptops with manufacturer utility software (Dell Power Manager, Lenovo Vantage, ASUS Armoury Crate). Switch to “Performance” or “Cool” fan profile during heavy work; switch back to “Quiet” for normal use.
Surface and environment
This sounds obvious but I see it constantly: laptops on beds, sofas, carpets, or thick fabric block intake vents underneath. The fan spins but pulls almost no air. Within 10 minutes you’re throttling. Use a laptop on hard surfaces only, or invest in a cheap laptop stand with airflow gaps. Even an upturned plastic kitchen rack works.
For desktops: check that the PSU and case fans actually have clearance behind the tower. PCs tucked tight against a wall or inside a closed desk compartment have nowhere to exhaust hot air. The case interior temp climbs steadily until everything thermal throttles. 4-6 inches of space behind the case is the bare minimum.
When to suspect malware
A CPU pegged at high usage by an unknown process — especially one with a random alphanumeric name in Task Manager — can be a cryptocurrency miner. These are sneaky; they sometimes throttle themselves down when Task Manager opens. Signs: high CPU when idle, fans never settling down even when not using the PC, slight performance drops that didn’t exist before.
Run a full Windows Security scan → Defender Offline Scan (Settings → Privacy and security → Windows Security → Virus & threat protection → Scan options → Microsoft Defender Antivirus (offline scan)). This boots into a clean environment to scan, catching things that hide while Windows is running normally.
| Symptom pattern | Likely cause | First fix to try |
| Sudden high temp after Windows update | Telemetry / indexer running | Let it finish (2-4 hours), then check again |
| Gradual increase over months | Dust accumulation or paste degradation | Clean heatsink; consider repaste if old |
| Hot from cold start, no load | Background process consuming CPU | Task Manager → end the top CPU process |
| Only hot during games | GPU dumping heat; weak case airflow | Improve case ventilation; check GPU temps |
| Hot even at 10% CPU usage | Cooling problem, not software | Dust cleaning + paste replacement |
The combination of Task Manager (immediate diagnostic), HWMonitor (real temperatures), and a 15-minute dust blowout resolves the vast majority of overheating cases. Repaste only enters the conversation when those don’t help and the machine is more than three years old.
Undervolting — controversial but effective
This one’s optional and not for everyone, but worth knowing. Most CPUs ship with slightly higher voltage than they actually need to maintain stability. Lowering the voltage by 50-150mV reduces heat output noticeably without affecting performance — same clock speeds, less heat, less power draw.
Tools: Intel XTU (Intel CPUs), Ryzen Master (AMD), or ThrottleStop (Intel laptops). Drop the voltage offset by -50mV → run a stress test (Cinebench R23 multi-core, 10 minutes) → if stable, drop another -50mV → repeat until you crash or freeze, then back off 50mV from the last stable value.
Some recent Intel CPUs (12th gen onwards) have undervolting locked at the BIOS level for security reasons. If the option is greyed out or doesn’t apply: it’s been disabled, no workaround. AMD Ryzen and older Intel chips work fine.
Caveat: an unstable undervolt produces random crashes that look like other problems entirely. If you undervolt and start seeing blue screens or freezes weeks later, set everything back to default first before debugging anything else.
Laptops with chronic overheating
Some laptop models are genuinely undercooled from the factory — common in thin-and-light designs where the chassis can’t dissipate enough heat for sustained CPU loads. If your machine has always run hot since new, no software trick changes that physics. Practical workarounds:
- Use the laptop on a metal stand with proper airflow underneath
- Set the power profile to “Best power efficiency” when on battery
- Cap the CPU at 80% max state (advanced power settings)
- Avoid running demanding apps with the lid resting closed against a docking station setup — heat builds up faster
- Take occasional 5-minute breaks during heavy work to let the system cool
None of this is glamorous, but it’s the realistic option when you can’t replace the hardware. A cooler with active suction (laptop cooling pad) can drop temps 5-8°C — modest but meaningful for a borderline-throttling system.
When new hardware is the right answer
If a desktop is 6-8 years old, the CPU cooler is generic stock, and you regularly do demanding work — software fixes have their limits. A £30 aftermarket air cooler (Cooler Master Hyper 212, DeepCool AK400) drops temps 10-15°C compared to stock coolers. AIO liquid coolers (NZXT Kraken, Corsair iCUE) drop another 5°C and are quieter under load.
For laptops, “new hardware” usually means a new laptop. There’s no realistic CPU cooling upgrade path in most thin laptops. If the machine is throttling constantly despite all software optimisations and a professional cleaning, it’s reached the end of its useful life for sustained CPU work — though it may still be fine for light browsing and document editing.
One pattern worth flagging because it confuses people: Windows 11’s resource monitor sometimes shows CPU usage in “Logical Processors” view that differs from the simple Task Manager percentage. A process showing 25% usage on a 4-core/8-thread system is fully maxing two logical processors but appears low in the overview. The temps don’t lie though — if HWMonitor shows 90°C, something is genuinely working the CPU hard regardless of what the percentage says. When in doubt, trust the thermometer over the percentage.
The realistic order of operations for any overheating PC: identify what’s using the CPU (Task Manager), measure actual temps (HWMonitor), reduce software load (kill startup apps, fix runaway processes), then address cooling (clean dust, check fan curves, repaste if old). Skipping straight to cooling work without identifying software causes wastes time on machines where a single rogue process is the real problem. Our guide on Windows 11 Action Center Not Working covers an adjacent issue.
