An aerobic septic system has more moving parts than a conventional tank, so it fails in more ways. Most problems fall into four groups: the system is not getting power, air, or water moving, or the alarm is telling you something. This guide shows how to sort a symptom into the right group, what you can check safely, and when to call a provider.
This is general information. It does not replace your system manual, your permit, your local authority or a qualified provider, and the layout of your own system decides what applies to you.
Start with the alarm panel
Most aerobic systems have a control panel with a warning light and often a buzzer. Before you look at anything else, note what it shows and whether the buzzer is sounding. The panel is the system’s own description of the problem, and it narrows the search a lot.
- No lights, no sound: check the power supply first (see below).
- Alarm light on: read the manual for what that light means on your model, and use our guide to what to check when the alarm goes off.
- Buzzer on, light off: silence it only if your manual says it is safe to do so, then report the problem.
Check the power, and stop there if it keeps tripping
A tripped breaker or a failed GFCI is the most common cause of a system that suddenly stops. Check the breaker that feeds the control panel. Reset it once. If it trips again, do not keep resetting it. A breaker that trips repeatedly means something is drawing too much current or leaking to ground, and a provider needs to find out what.
Symptoms and what they usually point to
Smells, indoors or in the yard. Odour can come from a blocked or unvented plumbing vent, a damaged lid seal, a stalled air supply, or a system that is overloaded. Our guide to septic smells explains how to tell where the smell is coming from. Rotten-egg odour near the unit can mean the aeration has stopped.
Slow drains or water backing up. This is a hydraulic problem: the system cannot move water through as fast as the house sends it. Check whether the alarm is on and whether the effluent pump is running. Reduce water use for a few days while you call a provider. Do not pour drain cleaners or chemicals into the system to clear a drain; they can kill the bacteria that do the treatment.
Sprinkler heads not spraying. One head or all of them, the answer changes the diagnosis. See our guide to sprinkler heads that are not spraying.
Air pump noise or no sound at all. A pump that has stopped, or one that runs continuously and never stops, both need a provider. Our guide on a pump that is not working covers the signs to report.
Wet or spongy ground over the field. Effluent may be reaching the surface, which is a health hazard and a permit issue. Keep people and pets away from the area and call your provider the same day.
What you may check yourself
- The breaker and the panel’s power light.
- Whether the alarm light is on, and which one.
- Whether you can hear the air pump run.
- Which sprinkler heads are working, and whether any ground is wet.
- Whether anything changed recently: heavy rain, a freeze, a power cut, a lot of guests, or a vehicle on the field.
What you should not do yourself
- Open the tanks, pump chambers or aeration compartments.
- Adjust the air supply, the float switches or the timer.
- Pour chemicals, bleach, drain cleaners or enzyme products into the system.
- Repair or replace electrical components, pumps or sprinkler heads on a permitted system.
In many places this work is limited to licensed personnel, and a mandatory maintenance contract may cover it. Doing it yourself can breach that contract. Check your agreement before you touch anything.
Call your provider, and what to tell them
Before you call, write down the answers to five questions: what the alarm shows, when the problem started, whether it followed rain or a power cut, which parts of the system are affected, and what you already checked. A prepared call is the fastest way to a useful visit. Our free service call log has space for these notes.
About this guide
This is educational information only and not a diagnosis of your system. What is correct for your property is set by your manual, your permit, your permitting authority and a qualified provider.
Last reviewed: 1 November 2026.