Condensate Leak in the Attic in Hillsborough, CA

Condensate Leak in the Attic in Hillsborough

When an air conditioner runs, it pulls moisture out of the air and drips it into a pan under the evaporator coil. That water leaves through a primary condensate line, and when the line clogs the water has nowhere to go but up and over the pan. In a Hillsborough attic install, the first sign is almost always a stain on the ceiling below, sometimes a soft spot in drywall before anyone notices a drip.

Hillsborough's marine-influenced air is humid enough that coils produce steady condensate even with the moderate cooling these homes need, and the drain line collects biological slime over a season or two. That slime is what plugs the line. It is one of the most common service calls we get from attic and closet installs, and it is almost always a single fixable problem: a clogged line, a tired condensate pump, or a float switch that never cut the system off before the water rose.

Most of these estates run more than one air handler, often one per wing or floor, so we trace the leak back to the specific unit that is overflowing rather than assuming. The grade and the long routing on these wooded hillside lots also matter, because a drain that was pitched wrong at install will pool and overflow no matter how clean the line is.

Common causes

Clogged primary condensate line. Algae and biological sludge build up inside the drain and block it. Water backs up into the pan and over the edge. We clear the line with a wet vacuum at the termination and flush it, then confirm flow by pouring water through the pan and watching it drain. We point out where a cleanout tee belongs if the line doesn't have one.

Float switch that never tripped. The safety float in the pan or drain line is supposed to shut the AC off when water rises. When it's missing, miswired, or stuck, the system keeps running and keeps making water until it spills. We test the switch by lifting the float and confirming the system cuts out, and add one where an attic unit has none.

Failed condensate pump. Some of these attic and closet units sit below their drain exit and rely on a small pump to lift water out. When the pump motor burns out or its own float sticks, the reservoir fills and overflows. We test the pump under power, check its check-valve, and replace the unit if it won't reliably clear its tank.

Cracked or rusted primary pan. An older galvanized or plastic pan can crack or corrode through, so water leaks straight to the ceiling even with a clear drain. We inspect the pan with a flashlight and mirror and confirm it holds water. A cracked pan gets replaced, not patched.

Improper pan slope from the original install. If the air handler sits dead level or tipped the wrong way, water pools at the far corner instead of running to the drain. We check the pan's pitch and shim the unit so it drains toward the fitting. On these long hillside routings we also verify the drain line keeps a downhill slope its whole run.

Emergency drain pan filling up. The secondary pan under the air handler is the last line before the ceiling. If you're seeing water in it, the primary system already failed upstream. We treat a wet secondary pan as the warning it is, find why the primary overflowed, and make sure its float switch will catch it next time.

How we diagnose it

Confirm which air handler is overflowing, since most Hillsborough homes run several independent systems.
Pour water through the primary pan and watch where it goes: clean drain, clog, or a pan that won't hold.
Test the float switch by lifting the float and verifying the system actually shuts down.
Inspect the primary and secondary pans for cracks, rust-through, and standing water.
Check the drain line slope along its full run and confirm a condensate pump, if present, clears its tank under power.

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

Condensate Leak in the Attic in Hillsborough: common questions

Do you actually cover Hillsborough, or are you based across the Bay?

We're based in San Ramon and run the whole Bay Area, Hillsborough included. We route by the day's calls across the Peninsula, so we'll give you a real arrival window when you call rather than a vague all-day promise. A ceiling stain that's still spreading gets treated as same-day where we can.

Hillsborough summers are mild. Why would my attic AC leak at all?

Mild doesn't mean dry. The marine air here carries enough moisture that your coil still pulls real condensate whenever the AC runs, and that water feeds the same drain line that clogs everywhere else. The leak is about the drain, not the heat, which is why we see this on Peninsula homes that barely run their cooling.

There's water in the emergency pan but no ceiling stain yet. Is that urgent?

Yes, that pan is the last thing standing between the leak and your drywall. Water in it means the primary drain already failed and the only reason you don't have a stain is that the secondary caught it. Get it looked at before the secondary fills too. We find the upstream cause and confirm the float switch will shut the system off next time.

Nearby and related

Condensate Leak in the Attic near Hillsborough: Menlo Park · Palo Alto .

This is usually a ac repair in Hillsborough job. See our ac repair overview or the Hillsborough service area.