TL;DR
Humidity faults abort the cycle because EtO sterilization requires a relative humidity above 30% to kill spores. Check the humidification system and chamber humidity sensor calibration.
What you might see
- cycle abort alarm at the humidity conditioning phase
- chamber relative humidity reading below the set-point minimum
- steam injection valve not opening during conditioning
- cycle abort repeating on consecutive runs
Likely causes
Steam supply pressure below the conditioning minimum
Steam injection valve seat fouled with mineral deposits, restricting flow
Chamber humidity sensor calibration drift or sensor failure
Chamber door seal leak allowing humidity to escape during conditioning
Required tools
- Reference hygrometer for sensor calibration
- Steam pressure gauge
- Valve descaling kit
- Replacement door seal
Safety first
- The sterilizer chamber is an oxygen-enriched or EtO-contaminated environment depending on cycle phase. Follow the gas-safe protocol before opening any chamber port for sensor access.
- Steam injection systems operate at elevated temperature and pressure. Isolate and bleed the steam supply before working on the injection valve.
Procedure
- 1
Review the cycle record to identify at which humidity level the fault occurred and how quickly the humidity dropped.
- 2
Check the steam supply pressure at the sterilizer steam inlet. Compare to the minimum conditioning pressure in the process specification.[1]
- 3
Test the steam injection valve by running the manual conditioning test from the controller diagnostics menu. Confirm the valve opens and steam enters the chamber.
- 4
Inspect the steam injection valve for mineral deposit buildup on the seat. Descale or replace the valve insert if flow is restricted.
- 5
Calibrate the chamber humidity sensor against a reference hygrometer at two humidity points. Replace the sensor if calibration fails.[1]
- 6
Inspect the chamber door seals for cracking or deformation. Replace the door seal if any section is damaged.
- 7
Run a cycle without product (an empty chamber test run) after repairs. Confirm the humidity conditioning phase reaches the validated minimum level.
Sources
Steris Steris EtO Sterilizer EtO Sterilizer general technical documentation, Steris
Steris EtO sterilizer general chamber conditioning and sensor calibration procedures per ISO 11135 (general)
More guides for Steris Steris EtO Sterilizer
How to fix chamber pressure leak during EtO dwell on a Steris EtO Sterilizer
Pressure drop during the EtO dwell phase usually means a door seal failure, a valve seat leak, or a chamber penetration fitting loose. Perform a nitrogen leak test before restarting with EtO.
How to fix EtO residual levels above specification on a Steris EtO Sterilizer
High EtO residuals on the product are usually insufficient aeration time, an aeration chamber temperature below set-point, or a product load configuration that blocks airflow. Extend aeration and verify chamber temperature first.
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