First, check these common issues:

Problem: Temperature above -190°C

Common causes:

  1. Vacuum seal failure – Most common
    • Symptom: Rapid temperature rise
    • Fix: Recertification/replacement needed
    • Cost: £50-150 for testing
  2. High evaporation rate – Partial vacuum loss
    • Symptom: Increased refill frequency
    • Fix: Vacuum re-certification
    • Cost: £100-200
  3. Refill interval exceeded – Normal operation
    • Symptom: Temperature drops as LN₂ evaporates
    • Fix: Schedule refill sooner
    • Cost: £20-35 per refill

What to do:

  1. Check when last refilled (if >8 weeks, refill immediately)
  2. Verify refill port is functioning (try adding small amount)
  3. Contact supplier for professional inspection
  4. Use dry shipper as emergency backup if available

Sample safety:

  • Samples remain viable down to approximately -150°C
  • Even failed dewars maintain samples for 30+ days
  • You have time to arrange repairs/replacement