Winterising is the single most important maintenance step many Melbourne evaporative cooler owners skip — and the one that most reliably leads to expensive start-up problems the following September. The reasons come down to what happens inside a sump left with water over winter: mineral scale hardens to a cement-like deposit, and biological contamination — including conditions that favour Legionella bacterial growth — can establish in the stagnant warm water.
This guide covers when and how to winterise a Melbourne evaporative cooler, what happens if you skip it, and how to get the system properly ready for the following cooling season.
Why Winterising Matters in Melbourne
Melbourne’s winter is mild compared to inland Victoria, but daytime temperatures still reach the 12 to 18°C range — warm enough for biological growth in stagnant water. An un-drained sump sitting with water from April through to September provides conditions for Legionella bacteria to establish and multiply, particularly if the sump has any accumulated scale or biofilm from the previous season.
The secondary issue is mineral scale. Melbourne’s mains water contains dissolved calcium carbonate. When evaporation concentrates this mineral and then the water sits stagnant over winter without being cycled through the system, the calcium deposits harden into a cement-like scale on the sump walls, pad frames, and distribution troughs that is significantly harder to remove than fresh scale from active use.
When to Winterise — Melbourne Timing
The practical window for Melbourne evaporative cooler winterising is April to May. The benchmark is when the Bureau of Meteorology’s 14-day forecast shows no days above 28°C coming — at that point the cooling season is effectively over for the year.
In Melbourne’s typical climate, this occurs in the first two weeks of April following an El Niño summer, or may extend into late April or early May in La Niña summers when Melbourne experiences later warm periods. The Melbourne Easter long weekend is a convenient annual reminder for many households.
Spring start-up should be booked for late September — approximately 12 weeks before the winterising date. Melbourne’s first hot days (35°C+) can arrive as early as late October, so having the system serviced and ready by 1 October is a sensible target. Melbourne HVAC technicians fill up quickly in September — book in August to secure a slot.
Step-by-Step Winterising Procedure
The following procedure covers a standard Melbourne rooftop evaporative cooler. Always work safely on roofs — use a properly secured ladder and do not work alone.
- Turn the system off at the wall controller and confirm no cooling demand is needed.
- Switch off the circuit breaker for the evaporative cooler at the main switchboard.
- Turn off the water supply tap at the roof unit — typically a ball valve adjacent to the unit on the roof or in the ceiling space near the roof penetration.
- Drain the sump: open the drain plug at the base of the sump. Allow the sump to drain fully. On units without a drain plug, the pump can be used to pump the sump dry.
- Wipe the sump interior with a damp cloth to remove any loose scale or sediment. Assess scale buildup — if scale is heavy, book a professional descale for the spring start-up.
- Check pad condition and note whether replacement is needed before next season.
- Refit the drain plug firmly after the sump is fully dry.
- Fit the winter cover over the entire roof cabinet. Check that the cover fits securely and will not be dislodged by Melbourne’s winter winds.
- Inside the home: confirm the wall controller is switched off. If the ceiling outlets do not have automatic dampers, fit blanking plates to reduce cold draught entry.
Consequences of Not Winterising
A Melbourne evaporative cooler that is not winterised will typically present these issues at the following spring start-up:
- Heavy mineral scale in the sump requiring chemical descaling and mechanical removal (significant additional time and cost at the spring service)
- Biological contamination of the sump, pads, and distribution system requiring professional sanitisation before the system is safe to run
- Pump or float valve stuck by scale buildup
- Distributor nozzles and drippers blocked by concentrated scale deposits
- In steel-sump units: accelerated corrosion from the combination of moisture, scale, and biological acids over winter
The cumulative cost of these spring remediation tasks adds considerably to what would otherwise be a standard annual service — far outweighing the $250 to $380 cost of a proper winterising service done in April or May. See our water quality and Legionella guide for more detail on the health risks of biological contamination in neglected systems.
Spring Start-Up — Reopening the Season
In September, the spring start-up service reverses the winterising process: remove the winter cover; restore water supply; inspect pads and replace if needed; flush the sump with fresh water; check pump and motor operation; run the system on full cooling mode for five to ten minutes and confirm even water distribution across all pads. Book the spring service in August to secure a September slot.
See our annual maintenance checklist for the complete task-by-task breakdown of both the spring start-up and end-of-season winterising procedures.