CPU Fan Not Spinning: Check the Header Connection
A technician is assembling a new desktop computer. After installing the CPU, heat sink, and RAM, the technician powers on the system. The fans spin for a moment, then the system shuts down. The CPU fan does not spin at all. Which of the following is the MOST likely cause?
Quick Answer
Motherboards include a built-in safety feature specifically to protect the CPU from overheating due to a failed or disconnected cooling fan, and that protection is exactly what is triggering the shutdown described here. The CPU_FAN header is monitored by the motherboard, which expects to see a tachometer signal confirming the fan is actually spinning; if no such signal is detected, most motherboards will shut the system down within seconds of powering on rather than allow the CPU to run without active cooling, since even a brief period without cooling could damage the processor under load. In this scenario, the fans spin briefly and the system shuts down almost immediately, but the important detail is that the CPU fan specifically does not spin at all, distinguishing this from a general power or short-circuit problem, since other fans clearly do receive power and begin operating. If the CPU fan's connector was plugged into a different header, such as a case or system fan header, rather than the specific CPU_FAN header the motherboard monitors for this safety check, the motherboard would have no way to confirm CPU cooling is present and would shut the system down as a protective measure. Whenever a new build shuts down almost immediately after power-on and the CPU fan specifically is the one that fails to spin while other fans work, check that its connector is seated in the correct CPU_FAN header rather than assuming a fan or PSU failure.
⚠ Common exam trap
The 220-1101 exam often tests the distinction between a component being faulty versus simply not connected; the trap here is that candidates may assume the CPU is dead or incompatible when the real issue is a missing or loose fan header connection.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CPU fan connector is not plugged into the CPU_FAN header.
The CPU fan connector must be plugged into the motherboard's CPU_FAN header for the fan to receive power and for the system to detect fan operation. Many motherboards have a safety feature that shuts down the system within seconds if no fan signal is detected on the CPU_FAN header, preventing CPU overheating. Since the CPU fan does not spin at all, the most likely cause is that the connector is not attached to the correct header.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The CPU is not compatible with the motherboard.
Why it's wrong here
An incompatible CPU usually prevents POST entirely, often with no fan activity or a persistent error, rather than fans spinning briefly then stopping with only the CPU fan dead. It is tempting because socket mismatch is a real assembly risk, and it would be correct if the board refused to start at all.
When this WOULD be correct
This would be correct in a scenario where the system fails to POST with no display output and the motherboard emits beep codes indicating a CPU issue, or if the CPU is physically incompatible (e.g., wrong socket) and the system immediately shuts down without any fan activity.
- ✓
The CPU fan connector is not plugged into the CPU_FAN header.
Why this is correct
Many motherboards halt POST immediately when no tachometer signal arrives on the CPU_FAN header, cutting power after a brief spin. Connecting the fan to that header restores the RPM reading and allows the system to complete boot.
- ✗
The RAM is not seated properly.
Why it's wrong here
Improperly seated RAM typically triggers a boot failure with beep codes or no POST display, yet the CPU fan header would still receive power and spin. It is tempting because RAM seating is a frequent assembly fault, and it would be the likely cause if the system failed POST without the fan symptom.
When this WOULD be correct
If the question described a system that powers on but displays no video output and emits a series of beeps (e.g., continuous long beeps), then improperly seated RAM would be the most likely cause.
- ✗
The power supply is insufficient.
Why it's wrong here
An undersized power supply usually causes shutdowns under heavy load or during POST, not an immediately dead CPU fan while other fans briefly spin. It is tempting because insufficient wattage is a classic build error, and it would be correct if the system failed only once components drew full power.
When this WOULD be correct
A technician installs a high-end GPU and multiple drives in a system. Upon power-on, the system fails to boot or randomly shuts down under load. The power supply wattage is below the recommended minimum for the components, making it the most likely cause.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The CPU fan connector is not plugged into the CPU_FAN header.Correct answer▾
Why this is correct
Many motherboards halt POST immediately when no tachometer signal arrives on the CPU_FAN header, cutting power after a brief spin. Connecting the fan to that header restores the RPM reading and allows the system to complete boot.
✗The CPU is not compatible with the motherboard.Wrong answer — click to see why▾
Why this is wrong here
The system powers on briefly and then shuts down, with the CPU fan not spinning at all. An incompatible CPU typically prevents POST entirely or causes continuous beeping, not a momentary power-on with a non-spinning fan.
★ When this WOULD be the correct answer
This would be correct in a scenario where the system fails to POST with no display output and the motherboard emits beep codes indicating a CPU issue, or if the CPU is physically incompatible (e.g., wrong socket) and the system immediately shuts down without any fan activity.
Why candidates choose this
Candidates may confuse symptoms of CPU incompatibility (no POST, beep codes) with the described behavior, or they might assume that a non-spinning CPU fan is due to the CPU not being recognized.
✗The RAM is not seated properly.Wrong answer — click to see why▾
Why this is wrong here
Improperly seated RAM typically causes beep codes or a blank screen, not a system that powers on briefly then shuts down with a non-spinning CPU fan. The fan behavior points to a power or connection issue specific to the CPU fan.
★ When this WOULD be the correct answer
If the question described a system that powers on but displays no video output and emits a series of beeps (e.g., continuous long beeps), then improperly seated RAM would be the most likely cause.
Why candidates choose this
Candidates may associate any failure to boot with RAM issues, as RAM is a common culprit for POST failures, and they overlook the specific symptom of the CPU fan not spinning.
✗The power supply is insufficient.Wrong answer — click to see why▾
Why this is wrong here
In this scenario, the system powers on briefly and then shuts down, with the CPU fan not spinning at all. An insufficient power supply would typically cause instability or failure to boot, but it would not specifically prevent the CPU fan from spinning while other fans work.
★ When this WOULD be the correct answer
A technician installs a high-end GPU and multiple drives in a system. Upon power-on, the system fails to boot or randomly shuts down under load. The power supply wattage is below the recommended minimum for the components, making it the most likely cause.
Why candidates choose this
Candidates may attribute any power-related symptom to an insufficient power supply, overlooking that the specific symptom (CPU fan not spinning) points to a connection issue rather than a power capacity problem.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Power Supply Units and Connectors
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is assembling a new desktop computer. After installing the CPU, thermal paste, and heatsink, the technician connects all power cables and turns on the system. The fans spin, but the system shuts down after about 10 seconds. Which of the following is the MOST likely cause?
easy- A.The CPU is not compatible with the motherboard.
- ✓ B.The heatsink fan is not connected to the CPU fan header.
- C.The power supply is insufficient wattage.
- D.The RAM is not seated properly.
Why B: The correct answer is B: the heatsink fan is not connected to the CPU fan header. Many motherboards perform a POST check that detects no tachometer/RPM signal on the CPU_FAN header and will halt the boot or power off within seconds to prevent the CPU from overheating, which matches the symptom of fans spinning briefly then shutting down after about 10 seconds. An incompatible CPU (A) typically prevents the system from starting at all or produces a beep code rather than a delayed shutdown, and it would not be affected by the fan header. Insufficient PSU wattage (C) usually causes shutdowns under load or instability rather than a consistent 10-second cutoff at idle, and improperly seated RAM (D) normally results in no POST, beep codes, or a blank screen rather than a timed power-off.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.