SKETCH of a typical aerobic treatment unit tank, aerator, chamber Aerobic Septic System Troubleshooting
List of Problems in Aerobic Septic Systems

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Aerobic septic system installation, codes, & problem diagnosis:

This article discusses problems that occur in aerobic septic systems, also known as aeration septic systems or fine-bubble septic aerators. We identify things that cause problems with or harm aerobic septic systems.

These include flushing chemicals or salt into the aerobic system, electrical problems with the ATU pump or sprayer motors, odors and smells, pipe blockages, sprinkler head clogs or failures, and other aerobic septic system snafus.

At this website are designs and products for aerobic septic treatment units (ATUs) for onsite waste disposal, also called fine bubble aeration systems. We address aerobic septic system design, features, inspection, repair, and maintenance. Product sources are also listed.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Aerobic Treatment Unit Problems

SKETCH of a typical aerobic treatment unit tank, aerator, chamberArticle Contents

Don't Flush into Aerobic Septic Systems

Drugs: Systems serving homes (or nursing facilities) where occupants are consuming large quantities of medications, particularly antibiotics or possibly chemotherapy drugs, can be rendered inoperative if the antibiotic or drug level concentration is sufficient to kill the microbes in the ATU.

Disinfectants: Use of improper septic effluent disinfectant in aerobic systems: be sure to use the proper disinfectant in order to avoid both environmental contamination and violation of federal law.

See AEROBIC Septic System Disinfection with Calcium Hypochlorite and

AEROBIC Septic System Disinfection with Chlorine Tablets for details.

Filter clogging: I have received complaints of frequent outlet filter clogging on someaerobic septic systems. I speculate that the cause may have been a fault in the upstream solid-holding tank(s) such as a broken or missing baffle, use of the system beyond its design load, or perhaps improper use of aseptic additive or chemical which may have increased the level of suspended solids.


Salt: Systems serving homes with hard water and which use a water softener can be rendered inoperative ifhigh levels of brine are discharged into the ATU. Water softener backwash and brine will need to be discharged to a separate drywell.

Overloading: A residential ATU is at risk of being overloaded and failing to adequately treatits effluent if it has not been properly sized during its design phase.

Aerobic Septic System Alarm Troubles

Apologies for having to ask you to "click again" - for space and clarity we move this topic.

If you are having problems with the alarm system for an aerobic septic system or ATU alarm please see AEROBIC SEPTIC ALARM SYSTEMS where we have posted a checklist of things to inspect, try, or repair.

Aerobic ATU Septic System Electrical Problems

Reader Question: aerobic septic system problems following electrical storm

(June 22, 2014) Db said:
We had an electrical storm a few weeks ago and some how the breaker got tripped to entire system. I did not notice this until earlier this week. What problems could I be looking at. I am very regular about tablets and consistent with not putting damaging products into the system.



I agree that most aerobic septic systems are intended for continual operation. When the aerator pump stops the level of treatment in the tank falls substantially, risking discharge of inadequately-treated efflulent into the drainfield. If floating solids are discharged into the fields the field life is reduced as field clogging is sped up.

The best you can and should do is return the system to proper operation. Don't try extra products or additives, chemicals, treatments unless they are specifically required by the manufacturer of your aerobic system. Such additives are generally not needed, ineffective, and often illegal.

Provided your system did not discharge large amounts of solids into the fields you may not see a significant impact. If you want to be more optimistic or pessimistic you could inspect any distribution boxes or control point downstream from the treatment tank to look for deposits of solids.

Question: no power to the ATU pump

(July 30, 2015) christine said:
speedy rooter, the company I have a contract with for my aerobic septic system did an inspection 3 days ago. They called me today and said there's no power going to my system and that all three tanks a full.

I checked my circuit breakers and can't find anything amiss, I don't see a switch that says septic system either. Speedy Rooter told me I need to get an electrician out here to fix it and then after that I can call them to come pump it. The electrician company are saying they can get out here in four days. I'm very nervous about this. Any advice would be appreciated.



Sounds difficult. I agree with Speedy Rooter. Try calling some more electricians to find someone who can assist you sooner.

If your system uses an effluent pump operated by a float switch a simple check for a stuck float could get the system working again. If not you need an electrician.

Your electrician will probably check for power at the ATU system pump or effluent pump or sprinkler pump and work backwards to find an open switch, control or circuit.

Aerobic Septic System Aerator Pumps, Effluent Pumps & Pump Control Problems

Reader Question: is it normal for the septic aerator pump to run continuously?

I have a 4 tank aerobic system that eventually sprays the treated water, should the aerator pump run 24/7? System serves our single family (just two of us) house. - S.R. 7/17/2013

Reply: normally the septic tank aerator pump should be left running 24/7

Not necessarily.

Some effluent treatment systems that use an above-ground spray system may run under control of a timer. These systems are not normally on all the time.

Some effluent pumping systems that move effluent from a septic tank or effluent tank to an up-hill effluent disposal system may run under control of an effluent level pump.

Some aerator pumps are designed to run under control of a timer while others are intended to run continuously and further are designed to be quiet and to run rather economically.

In fact since an aerobic septic system depends on aeration to maintain both healthy aerobic bacteria in the septic tank and to assure adequate wastewater treatment to meet the system operating specifications, you should leave the aerator pump on at all times.

Usually these are small aerobic system aeration pumps - about 1/6 to 1/3 hp. Some example data about operating cost include:

Using the Watts = Amps x Volts formula (which is technically right but crude), if your pump is running at 120V AC and draws 2 amps, it's drawing 240 watts - about the same as a heat lamp, or a typical window fan. By contrast, an attic fan draws about 370 watts, and a well pump, about 2,200 watts; or better, comparing with stuff that people leave running 24/7, a 20 cu. ft. automatic-defrosting or frostless refrigerator may draw about 800 watts.

Using the constant for converting electrical horsepower or hp to watts, 1 hp (electrical, with some simplifying assumptions) = 746 watts.

Watch out: But if your pump is noisy or rattling it may need repair or replacement. If you'd like to give us the brand and model of your aerobic system aerator pump we'd be glad to check with the manufacturer on this question.

Reader Question: problems with jet aerobic unit mixer motor

(Sept 18, 2014) Chris said:
I have a jet aerobics unit with a mixer. The mixer runs for about 10 minutes, then shuts off. The baffles are sitting relatively close to the mixer, maybe only an inch away.

If the mixer is hitting the baffles, would it cause the mixer to shut down? Any other reason it may be shutting off?


Chris, besides hitting an obstruction, clogged outlets or an overheating motor can make the motor shut down.

Also check for low voltage, and see ELECTRIC MOTOR DIAGNOSTIC GUIDE for more help.

Reader Question:

(June 27, 2014) Linda said:
Just had a new pump installed and it was left for 3 years. I cant get it to pump. Motor is working. Dont know what to do?


Pull the pump, check it for a clogged inlet or for damaged impeller parts, oe clogged outlet or check valve

Reader Question: no discharge from the aerator pump system

(July 17, 2014) Tammy said:

We have an aerator and we never have a discharge. We can see the water going in but never coming out. Can the water or waste going anywhere else?



depending on where you live and the type of aerobic septic system that has been installed, yes it is possible for wastewter to be disposed-of entirely below ground. The "aerator" - if I am guessing correctly at what you are describing - is in a septic tank in order to increase the level of treatment of the sewage; clarified effluent flows out of the septic tank to a disposal field. Some septic systems spray treated effluent above ground, others simply dispose of it in absorption beds.

(July 17, 2014) Tammy said:

We have a 3 chamber air jet system that is in the ground and a pipe that leads to the Creek. It drained for 9 years and now it still comes into the first chamber but we never see a discharge anymore. Would their still be absorption beds also? We have no problems otherwise.

Live in KY. We don't smell anything but do notice wetness around our brick steps. No other blockages either but like I said the water comes into the tank we can visibly see it but we never have a discharge anymore.

Correction it goes all the way into the chlorinator. Last chamber.

(July 17, 2014) Tammy said:
We have a system just liken at the top of the page. Jet aerator that leads out to creek for disposing. We liven in ky. It comes into the 3rd chamber but never leaves a discharge. It use to for nine years. No other problems.


Check for a bad float switch on the effluent pump.

Aerobic or ATU Septic System Piping, Lines, Blockages

Reader Question: we have a blockage in our aerobic lines and never pumped the tank for 12 years. Is the blockage due to the pump?

We have semi-blocked lines and we have a two-chamber ATU and has never had it pumped. We've lived on this site for 12 years. What can be the problem? Is it a bad pump, or is it overflowing? - Cody 12/1/11


Short answer: Cody depending on the number of occupants you may have fallen behind in septic tank pumping frequency. See SEPTIC TANK PUMPING SCHEDULE.

If a septic tank is not pumped often enough the risk is that the level of treatment falls and solids are pushed into the effluent disposal system causing clogging and sometimes the need for costly repairs. But without opening your system for inspection, one can't accurately guess further.

Details: A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with the septic system. The inspector will need to open the tank, check the operation of the aerator, disinfection system if any, and possibly inspect the effluent disposal system as well.

That said, if you never pump the septic tank the treatment level drops, solids get pushed into the effluent disposal system, and the system will first, contaminate the environment with under-treated effluent and second, will become clogged - that's in general. Of course the specifics for your system will vary.

You'll want your septic contractor to show you the working parts of the system, the maintenance that it requires, the maintenance schedule, etc.

Reader Question: broken septic line repair

(Apr 27, 2015) Anonymous said:
I have a question, or a possible problem? On residential site has been on basic well and septic tank, lines busted some 13 ft below and for a distance of another 12 ft, the end of the broken line I ran into the city lines.

Unfortunately for me the break happened on my side therefore responsible for all costs and excavations of property not to mention the all the permits, inspections, a lot of red tape. Is this a real possibility for my case or what need answers please any info anyone could provide would be extremely helpful. Thanks


Sorry Anon I don't understand the question. If you are asking if truly the property owner is responsible for repairing sewer line breaks on their own property, in most jurisdictions that is indeed the case.

When making repairs ask the plumber and excavator to let you see and photograph the actual damage (use our page bottom CONTACT link to find an email to send me some photos for commment). It may be we can discover a cause and avoid another break in the piping later. For example failing to bed the lines in sand or burying a sharp rock over the line can cause damage.

Reader Question: does an aerobic septic system need to be winterized?

I have recently purchased a new home with an aerobic system that has 2 sprinklers. Do I need to winterize the system or turn off the sprinklers in the winter? If so, what happens to the water? - Stevi 12/5/11


Stevi an aerobic septic system would be expected to be functional year round.

But I agree completely that if your system is installed in a freezing climate, and if it uses above-ground effluent spraying, that system cannot work properly in freezing weather. Something sounds wrong with the whole design.

In a climate exposed to freezing the aerobic septic system's piping, pumps, and any controls that pass water or effluent need to be protected from freezing by depth below the frost line or by location in a heated area.

Aerobic Septic System ATU Sprinkler Problems

We have moved this discussion to AEROBIC SEPTIC EFFLUENT SPRAY HEAD REPAIR

Odor & Smell Complaints at an Aerobic Septic System ATU

Question: my sewer smells really bad, it was pumped, I put in new yeast and chlorine, and my air pump is running

My sewer smell really bad i have had it pump out about 1 1/2 years ago new yeast chorine and my air pump is working what can i do - Mark 1/23/12


Mark, yeast is not a normal septic system. I would contact the manufacturer of your system and ask for their advice and for a copy of the instruction manual.

According to some expert sources [3] a slight odour from an aerobic septic system is normal but strong, persistent odors indicate that the system is not working normally.

I agree that a strong odor problem is unacceptable, not normal, and can be corrected.


(Aug 10, 2015) Sandy MacDonald said:
What can be done about fairly strong odors coming from an atu system. Are chlorine tablets recommended? Any suggestion would be appreciated



You need an aerobic septic system service company to take a look at your system. I would not amend the normal disinfection treatment specified for your particular system design before determining what's the actual problem. More speculation on my part, with no data about your system, would be mere arm-waving. Do keep us posted as we may be able to comment on what you're told or to suggest things to ask.

Other than an occasional mild odor right at the ATU, the system should not be stinking up the yard.

Reader Question: ATU system life: My home's septic system is 47 years old. Is it working right?

My home is 47 years old, so it would make my 's&p' septic system equally as old. I'm not sure if that is the correct term for my septic design because it is so old. I cannot find a diagram on your website that is comparable to what I think I have.

I have 1 -1000g tank with 1 lid, the solid are pumped from this tank. It is connected to a 2nd (1000g) tank, 50 feet away which is a 2 story tank. You can stand in upper portion of the 2nd tank as it is made of concrete and has a crock hole to the lower part. The bottom portion of the 2 story tank accumulates liquids coming from the 1st tank.

Once the liquids in the 2nd lower tank reach a certain level, a sump pump (hanging in the crock) assists in the discharge through an underground pipe that is laying on the ground in the woods another 50ft away. Because of its age ("grand fathered"), its my septic doing what it is supposed to be doing? - Kim 4/23/12


Kim very few septic systems that are basically untouched for 47 years would lead me, even knowing nothing about them, to opine that the system is performing as it should.

The design sounds thoughtful however, as if you have a dosing system = that is, the second effluent tank accumulates effluent in some volume before sending it to an absorption field.

But a pipe laying on the ground? That does not sound right at all. You didn't describe an aerobic septic system (maybe I missed that) and you didn't say in what state you are located, but no where in the U.S. or Canada are we permitted to discharge effluent from a septic tank right onto the ground surface from a distribution pipe such as you describe.

In some U.S. states it is permitted to use an air spray to distribute effluent that is discharged from an aerobic septic design (tank, aerator, separation baffles, holding tank or pumping chamber) that is certified to treat effluent to perhaps 95% or better.

But you are not describing such a system. A conventional septic tank treats effluent to a maximum of about 45% of what's needed. So you may be discharging sewage onto the ground surface.

Question: Clearstream aerobic system aerator diffuser diaphragm failures & life expectancy

2016/08/10 Rick said:
Great site. Can you tell me how often the diaphragm need to be replaced on the aerator for a clear stream system? Currently we are having to replace it every two years.


Smart question, Rick. I don't know.

I looked at some Clear Stream literature including the company's Clearstream ATU Maintenance Guide [PDF] and instructions.
The word "diaphragm" doesn't even appear in those procedures. However the instructions do give life expectancies for system parts including:

"Repair or replace aerator every 2-10 years". That "repair" could include the aerator diaphragm.

I would check that there's nothing obvious that would reduce the aerator life such as

Clearstream Aerobic Septic ATU Maintenance Checlist

Clearstream expects you to use a Clearstream agent to inspect and maintain the system - included in the system cost for the first 2 years. I'd take this repair question to that person first.

Then I'd contact Clearstream Wastewater Systems to ask their technical support if there's something we're missing in this question.


Continue reading at or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AEROBIC ATU SEPTIC PROBLEM FAQs - questions & answers posted originally at this page

Also see AEROBIC SEPTIC DIAGNOSTIC FAQs - more diagnostic questions about aerobic septic systems



Or see these

Aerobic Septic System Articles

Suggested citation for this web page

AEROBIC ATU SEPTIC PROBLEMS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Ask a Question or Search InspectApedia

Questions & answers or comments about problems with the operation of aerobic septic systems

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher - Daniel Friedman