What This Error Means
The “Fan Speed Error” — also displayed as “Fan Lost,” “Fan speed too low,” “Fan X error,” or “Fan RPM below threshold” — means your Antminer has detected that one or more cooling fans are not spinning at the minimum required RPM. The miner firmware continuously monitors fan speed through tachometer signals built into each fan. When a fan drops below the configured threshold (typically 2,000-3,000 RPM depending on model), the miner triggers this error and may shut down to prevent overheating.
This is a critical safety error. ASIC miners generate enormous amounts of heat — a full-size Antminer can produce 3,000+ watts of thermal energy. Without adequate fan cooling, chip temperatures can reach damaging levels within minutes. The firmware takes fan failures seriously and will halt mining rather than risk permanent hardware damage.
Common Causes
- Failed fan motor — The fan motor has burned out or seized. Fan motors in ASIC miners run 24/7 at high RPM and have a typical lifespan of 2-4 years. Motor bearing wear is the most common fan failure mode.
- Loose fan cable connection — The 4-pin fan connector has vibrated loose from the control board. ASIC miners generate significant vibration, and over months of operation, connectors can work their way out.
- Dust and debris in fan bearings — Dust ingestion has clogged the fan bearings, increasing friction until the motor can no longer maintain minimum RPM. The fan may spin slowly or intermittently.
- Damaged fan cable or connector — The fan cable has been pinched, cut, or the connector pins are bent or corroded, disrupting the tachometer signal or power delivery to the fan.
- Control board fan header fault — The fan connector port on the control board has failed, preventing it from reading the fan tachometer signal even though the fan is working properly.
- Incorrect fan type — A replacement fan was installed that does not have the correct pin configuration, tachometer output, or voltage rating for the miner model.
Step-by-Step Fix
Safety first: ASIC miner fans spin at high RPM and can cause injury. Always power off the miner before inspecting or replacing fans. Never stick fingers or tools into a spinning fan.
Step 1: Identify the Failing Fan
Check the miner web interface under the dashboard or system status. Fan speeds are typically displayed as Fan 1 (intake) and Fan 2 (exhaust). Note which fan is reading 0 RPM or abnormally low. If both fans show errors, the issue is more likely a control board or power problem than two simultaneous fan failures.
Step 2: Visual and Physical Inspection
Power off the miner. Look at both fans — can you spin each one freely by hand? A healthy fan should spin smoothly with minimal resistance. A seized fan will feel stiff or gritty. Check that no cables or debris are contacting the fan blades. Look for visible damage to the fan housing or blades.
Step 3: Check Fan Cable Connections
Trace the fan cable from each fan to the control board. Disconnect and firmly reseat the 4-pin connector. Inspect the pins for corrosion or damage. On many Antminer models, the fan connectors are on the edge of the control board — make sure they are fully inserted and that the plastic clip (if present) is engaged.
Step 4: Swap Fan Positions
Swap the intake and exhaust fans (or swap their connectors on the control board). If the error follows a specific fan to its new position, that fan is faulty and needs replacement. If the error stays on the same control board header regardless of which fan is plugged in, the control board header is the problem.
Step 5: Clean the Fans
Remove the fans from the miner. Use compressed air to blow dust out of the fan housing, blades, and bearing area. If the fan has a removable sticker on the hub, peel it back and apply a small drop of machine oil (sewing machine oil or similar light oil) to the bearing. Spin the fan by hand several times to distribute the oil, then reinstall.
Step 6: Replace the Fan
If the fan is confirmed dead, replace it. Antminer models use specific fan sizes and connectors — make sure you get a compatible replacement. Common Antminer fan sizes: S9/S17/T17 use 120mm fans, S19 series use 120mm or 140mm depending on variant. The replacement must have a 4-pin connector with tachometer output compatible with your model. D-Central carries replacement fans for all major Antminer models.
Step 7: Check Fan Speed Threshold Settings
Some custom or third-party firmware allows adjusting the minimum fan speed threshold. If you have modified this setting, ensure it is set appropriately. Setting it too high will trigger false fan errors even with healthy fans. Revert to default settings if unsure.
Advanced Diagnosis
Via SSH, check fan-related kernel messages:
ssh root@[miner-ip]
cat /var/log/messages | grep -i "fan"
# Look for specific fan error codes and RPM readings
# Messages like "fan lost" or "fan speed low" with specific RPM valuesMultimeter testing: You can test fan power with a multimeter. With the miner powered on (carefully), measure voltage at the fan connector. Pins 1 and 2 are typically power (12V) and ground. You should read approximately 12V DC. If voltage is present but the fan does not spin, the fan motor is dead. If no voltage is present, the control board is not supplying power to that header.
Tachometer signal testing: Pin 3 on the fan connector is typically the tachometer output. With the fan spinning, this pin should produce a pulsed signal. If the fan spins but the miner reports 0 RPM, the tachometer wire in the fan may be broken — the fan cools but cannot report its speed to the control board.
When to Get Professional Help
Seek professional ASIC repair if:
- The control board fan header is damaged — this requires board-level repair or control board replacement
- Multiple fans fail simultaneously — this may indicate a power delivery issue on the control board
- You cannot source the correct replacement fan for your model
- The fan error persists after replacing with a known-good fan, indicating a deeper electrical issue
D-Central Technologies stocks replacement fans for all major Antminer models and performs control board repairs including fan header replacement. Submit a repair request here
Affected Models
Fan speed errors affect all Antminer models. The S9 series is particularly prone to fan failures after 3+ years of continuous operation. S17 and T17 models use fans that are known for shorter lifespans. S19 and S21 series fans are generally more reliable but still wear out under continuous 24/7 operation. Models with shroud-mounted fans (like the S19 series) may also see fan errors if the shroud is misaligned or missing.
Related Error Codes
- Temp Too High / Over Temperature — Fan failure leads directly to overheating
- Chain X Only / Missing Hashboard — Thermal shutdown from fan failure can cause chain detection issues on reboot
- Low Hashrate — Thermal throttling from inadequate cooling reduces hashrate
- PSU Failure — Power supply issues can manifest as insufficient fan voltage
Frequently Asked Questions
Can I run my miner with one fan while I wait for a replacement?
Strongly discouraged. Running with one fan provides roughly half the cooling capacity, which is insufficient for most models at full power. The miner will likely overheat and trigger temperature protection within minutes. If you must run while waiting for a replacement, significantly underclock the miner to reduce heat generation — but even this is risky and not recommended.
Can I use a third-party fan instead of the original?
Yes, as long as the replacement fan matches the required specifications: same size, compatible voltage (usually 12V), compatible connector (4-pin with tachometer), and sufficient static pressure and airflow rating. ASIC miners require high-static-pressure fans due to the dense heatsink arrays. Standard PC case fans typically do not have enough pressure to push air through ASIC heatsinks effectively.
Why do both fans show errors at the same time?
Simultaneous failure of both fans is rare and usually indicates a control board issue rather than two dead fans. The control board may not be supplying power to the fan headers, or a firmware issue is preventing it from reading tachometer signals. Try reflashing firmware first. If the issue persists with the fans confirmed working by testing on another device, the control board likely needs repair.
How often should I replace ASIC miner fans?
Under continuous 24/7 operation, plan to replace fans every 2-3 years as preventive maintenance. Monitor fan RPM monthly — a gradual decrease in RPM over time indicates bearing wear. Replacing fans before they fail completely prevents unexpected downtime and protects your hashboards from thermal damage.