The short answer
On an older Cosmo dishwasher, a leak ranks differently: the door gasket has taken a permanent set, the hose clamps and fittings have relaxed over years of heat cycling, and the sump seals have aged. Check the gasket for hardness rather than for debris, and expect a fitting that has slowly relaxed rather than one that was never tightened.
What you are actually seeing
- A small leak that has grown gradually over months — Means: on-page
- The door gasket feels hard and no longer springs back when pressed — Means: on-page
- A damp patch under the machine that dries between cycles — Means: on-page
- Rust or a water mark on the floor under the machine — Means: on-page
- Leaking only on the longest and hottest cycles — Means: on-page
- Water standing inside the tub with a dry floor — Means: different-fault — Go to: cosmo-dishwasher-drainage-failure
- Condensation on the worktop above the door at the end of a cycle — Means: different-fault — Go to: cosmo-dishwasher-door-seal
- Body: Match what you see before you take anything apart. A small leak that has grown gradually over months. The door gasket feels hard and no longer springs back when pressed. A damp patch under the machine that dries between cycles. Rust or a water mark on the floor under the machine. Leaking only on the longest and hottest cycles. Some near-miss symptoms belong on a different page: Water standing inside the tub with a dry floor points at a drain fault, covered on cosmo-dishwasher-drainage-failure; Condensation on the worktop above the door at the end of a cycle points at normal venting rather than a leak, covered on cosmo-dishwasher-door-seal.
Causes, ranked for this machine
- A door gasket that has hardened and taken a permanent set — Why this rank: First on an older machine because rubber loses its spring with heat cycling, and the gasket is the part that sees the most of it
- Hose clamps and fittings that have relaxed over years of heat cycling — Why this rank: A joint that was tight for years can weep once the clamp relaxes, which matches a leak that grew gradually
- An aged sump or pump seal weeping only when the machine is hot — Why this rank: Explains a leak that appears only on long hot cycles and not on a quick wash
- A tub or sump that has corroded at a seam — Why this rank: Rust marks under the machine point here, and it is usually the end of the machine rather than a repair
- Debris in the gasket or over-dosed detergent — Why this rank: Still worth ruling out because it is free, but it ranks lower on a machine whose seal has visibly hardened
- Body: Ranked for a built-in kitchen dishwasher with an electronic control, a manual filter and a drain hose running to a disposer or an air gap. Most likely: A door gasket that has hardened and taken a permanent set. First on an older machine because rubber loses its spring with heat cycling, and the gasket is the part that sees the most of it. Next most likely: Hose clamps and fittings that have relaxed over years of heat cycling. A joint that was tight for years can weep once the clamp relaxes, which matches a leak that grew gradually. Third: An aged sump or pump seal weeping only when the machine is hot. Explains a leak that appears only on long hot cycles and not on a quick wash. Fourth: A tub or sump that has corroded at a seam. Rust marks under the machine point here, and it is usually the end of the machine rather than a repair. Fifth: Debris in the gasket or over-dosed detergent. Still worth ruling out because it is free, but it ranks lower on a machine whose seal has visibly hardened.
What to check, in order
- Press the door gasket with a finger and judge whether it springs back
- Note whether the leak happens only on hot cycles
- Dry everything under the machine and identify the first place that becomes damp
- Look for rust or long-standing water marks that date the leak
- Body: Each check rules out the causes above it. First, press the door gasket with a finger and judge whether it springs back. Second, note whether the leak happens only on hot cycles. Third, dry everything under the machine and identify the first place that becomes damp. Fourth, look for rust or long-standing water marks that date the leak.
Checks you can safely make yourself
- Press the door gasket along its length and note where it stays compressed rather than springing back — Tools: none — Time estimate: a few minutes
- Run a short cool cycle and a long hot cycle on separate days and note which produces the leak — Tools: notepad — Time estimate: two cycles
- Switch off at the breaker, dry the floor under the machine completely and lay paper down to find the first wet spot — Tools: paper, towel — Time estimate: one cycle
- Open the cabinet under the sink and check every clamp and fitting for weeping, tightening only by hand where accessible — Tools: torch — Time estimate: a quarter of an hour
- Look under the front of the machine with a torch for rust streaks or a long-standing water mark — Tools: torch — Time estimate: a few minutes
- Body: Checks an owner can make with the machine switched off at the breaker, or by watching a cycle. Step one: Press the door gasket along its length and note where it stays compressed rather than springing back. Tools: none. Time: a few minutes. Step two: Run a short cool cycle and a long hot cycle on separate days and note which produces the leak. Tools: notepad. Time: two cycles. Step three: Switch off at the breaker, dry the floor under the machine completely and lay paper down to find the first wet spot. Tools: paper, towel. Time: one cycle. Step four: Open the cabinet under the sink and check every clamp and fitting for weeping, tightening only by hand where accessible. Tools: torch. Time: a quarter of an hour. Step five: Look under the front of the machine with a torch for rust streaks or a long-standing water mark. Tools: torch. Time: a few minutes.
Safety first
Safety
Switch off at the breaker before reaching behind or under the machine, and dry the floor before you work. Water plus a live appliance under a kitchen cabinet is the most common way owners get hurt on this job. On a machine of this age, treat any connection under the sink as suspect before you touch it: corrosion and hardened insulation are both cumulative, and neither is visible until a panel comes off. Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. unplug-before-service
Where the owner fix ends
On an older machine, call a technician once the gasket is proven hard, the leak follows hot cycles, or there is rust under the machine. A hardened gasket is a reasonable repair; a corroded sump or tub seam on an aged machine is usually the point at which replacement is the honest answer.
Nearest pages of the same kind
Generalized information
This page is generalized across the Cosmo dishwasher line. Front-control and top-control machines, and panel-ready and stainless fronts, share the ranking above but not every part, and this page does not cover a specific model or control revision. Family- and model-specific pages, where they exist, are linked below.
Links: - [Common COSMO Dishwasher Problems](/blog/cosmo-dishwasher-problems) - [Cosmo Dishwasher: Abnormal Noise or Vibration](/blog/cosmo-dishwasher-abnormal-noise-2) - [Cosmo Dishwasher: Does Not Clean or Dry](/blog/cosmo-dishwasher-cleaning-performance-2) - [Cosmo Dishwasher: Controls, Display or Error Code](/blog/cosmo-dishwasher-control-fault-2)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
