Synology NAS Error Code 35: How to Fix It

Medium 30-60 minutes High Severity Verified June 2026
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Error Code
35
Brand
Synology
Product Type
nas
Severity
High
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Synology DSM Error Code 35 indicates that one or more cooling fans inside your NAS have failed or are not spinning at the expected speed. This is a high-severity alert because without proper airflow, your NAS can overheat quickly, potentially damaging hard drives, the CPU, and other internal components. You should address this error immediately to protect your data and hardware.
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Tools You'll Need

How to Fix Error Code 35

  1. Check DSM Notifications and System Logs

  2. Check Real-Time Fan Status in DSM

  3. Power Down the NAS Safely

    Always unplug the NAS from the power outlet before opening the chassis or touching internal components. Failure to do so can result in electric shock or damage to internal hardware.

  4. Open the NAS Chassis and Locate the Fan

    Ground yourself with an anti-static wrist strap or touch a grounded metal surface before handling internal components to prevent electrostatic discharge (ESD) damage.

  5. Clean the Fan and Vents

    Do not use a vacuum cleaner directly on internal components, as static discharge can damage sensitive electronics.

  6. Inspect Fan Connector and Cable

  7. Reassemble and Test

  8. Replace the Cooling Fan if Still Faulty

    Ensure the replacement fan is installed with the correct airflow direction. Installing it backwards will push hot air into the unit instead of exhausting it, worsening overheating.

  9. Monitor Temperature After the Fix

Parts You May Need

Cooling fan (80mm DC)
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Cooling fan (92mm DC)
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Thermal paste
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Cooling fan (80mm DC)
Check Price on Amazon
Cooling fan (92mm DC)
Check Price on Amazon
Thermal paste
Check Price on Amazon
Cooling fan (80mm DC)
Check Price on Amazon
Cooling fan (92mm DC)
Check Price on Amazon
Thermal paste
Check Price on Amazon
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When to Call a Professional

Contact Synology technical support or a certified NAS technician if: (1) the fan replacement does not resolve Error Code 35 and the error persists after confirming the new fan spins correctly; (2) you suspect the motherboard fan header is damaged or not delivering power to the fan; (3) your NAS is still under warranty — opening the chassis yourself may void the warranty, so check with Synology support first before performing DIY repairs. If your NAS has already overheated and drives are showing SMART errors or DSM is reporting drive warnings, consult a data recovery specialist before further troubleshooting.

Frequently Asked Questions

What does Synology Error Code 35 mean?
Synology DSM Error Code 35 means the system has detected a fan failure. One or more of the cooling fans inside your NAS is either not spinning or spinning below the minimum threshold RPM required for safe operation. This is a high-severity alert because overheating can damage your hard drives and shorten the lifespan of internal components.
Can I keep using my Synology NAS with Error Code 35?
It is strongly recommended that you do not continue using the NAS normally with Error Code 35 active. Without adequate cooling, internal temperatures can rise rapidly, increasing the risk of hard drive failure and data loss. Shut down the NAS and resolve the fan issue before resuming normal use. If you absolutely must keep it running briefly, ensure it is in a cool, well-ventilated area and monitor temperatures constantly.
How do I check my Synology fan speed in DSM?
Log into DSM and go to Control Panel > Hardware & Power. Click on the 'General' or 'Thermal' tab (the exact location varies slightly by DSM version). You will see real-time fan speed readings in RPM for each fan in the system. A reading of 0 RPM indicates a failed fan, while very low RPM may indicate a struggling or partially failed fan.
What size fan does my Synology NAS use?
Most desktop Synology NAS models use either 80mm or 92mm DC fans with a 3-pin or 4-pin header connector. The exact fan size depends on your specific model. Check the Synology hardware installation guide for your model on Synology's official support website, or physically measure the existing fan after opening the chassis. The fan size (e.g., 80x80x25mm) is usually printed on the fan's label.
Will Synology replace my NAS fan under warranty?
Synology offers a limited hardware warranty (typically 2–5 years depending on the product line) that may cover fan failure if the unit is within the warranty period and the failure is due to a manufacturing defect. Contact Synology support with your device serial number and the Error Code 35 details. Be aware that physical damage or modifications to the unit can void the warranty, so check with Synology before opening the chassis if your device is still under warranty.

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