Woson Tanco: false vacuum at rest and vacuum error in cycle
What happened
As reported in the case: before start, with the door open, the display showed a vacuum of -3.3 instead of the normal 0–0.3; after a cycle was started, pressure climbed to about +0.9, and after 5–7 minutes, around 50°C, a vacuum-building error (E12) appeared.
What was checked
- The vacuum pump was checked first — in this model it is mounted on the hose at the lower right of the unit.
- The vacuum line and the chamber seal area were inspected for a foreign object, since a large negative reading with the door open pointed to something holding vacuum in the circuit rather than a weak pump.
- The cycle behaviour (pressure rising to +0.9 before the fault) helped rule the pump out.
Cause
A small metal tooth from the gear of a dental contra-angle handpiece had entered the vacuum circuit and lodged under a rubber seal, partially restricting the line and creating the false vacuum reading.
What was done
The engineers removed the debris from under the seal and reassembled the circuit; a trial cycle with an empty chamber then ran without the vacuum error, and the unit went back into use after passing that test.
Safety
Chamber water, condensate and residues in a sterilizer count as potentially contaminated biohazard — wear gloves and eye protection when draining and cleaning, and confirm the repair with a full empty-chamber test cycle before the unit handles clinical loads again.
Lesson: Before condemning a vacuum pump, inspect the whole vacuum path for debris — instruments shed small parts that can lodge anywhere in the line and mimic a pump or sensor failure.
Covered in the course: Steriliser Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.