We had our roof gutters and solar panels professionally cleaned last week, and that night we had around 30mm of rain which resulted in water being all over the kitchen bench tops on either side of the sink and on the lounge room floor.
We expected that it must have been due to the work on the roof and called the business who inspected the roof and thought it must have been caused by the air conditioners, so we called our plumber.
The plumber very promptly resolved that the problem must have been caused by the downpipe that both air coditioners drain pipes connect to backing up and forcing water back up through the aircon drain pipes, and he recommended that we get a Y fitting installed with the cap sitting on it loosely.
A couple of nights later, we had around 75mm of rain and the cap was upside down on the ground but no more flooding in the house.
Whilst building inspectors, pest control operators and air conditioning service people strongly encourage property owners to plumb aircon drains into the storm water, our plumber is strongly opposed to the idea.
Fortunately, all the common areas of our residence are tiled so no water damage.
Unfortunately, the plumber suspects that the stormwater pipe leading out to the gutter must be restricted and we will need to get a camera inspection.