Replacing an Aerobic Septic Timer and Pump

This was an urgent project I did this weekend, I was out by my septic system for a couple hours and never heard the pump kick on. I finally got opened the lid to check out what was going on and found some major problems. I didn’t get pictures but, I can describe what I saw:
I have an older aerobic system, basically a regular septic but air gets pumped in to feed the bacteria resulting in a more efficient breakdown. From my reading some aerobic systems run 24/7 mine is an older style and runs based on the number of people using it. When I moved into my house, I paid the septic company to pump it and do an inspection, they said everything was good except for a broken timer. One of the two things I paid to get done when buying our house at a total of $230.
That leads to today when I opened the pump, I was angry to say the least. When they installed the pump they used a pump timer like this: Outdoor pump and daisy chained it to a timer like this: Indoor Timer.  The indoor timer wasn’t mounted to anything like the outdoor timer and had fallen into the mud in the septic cover and jammed up in the on position.  It was set ON/OFF every half hour the outdoor timer was set to ON/OFF for 15min each hour.  This effectively made it run 7.5 minutes each hour based on the recommend 8 minutes  for two people.  When the indoor timer fell and got stuck in the mud,  the septic was then set to 15 minutes every hour which was okay since my brother moved in and was renting the apartment.

Any system is only as good as the weakest link, in my case this was a cheap indoor timer running a very expensive septic system.  I directly wired in the pump into the electric bypassing the timers and it was dead, not sure if the timer falling in the mud were related or not since it was all dry now.  I went ahead and ordered a new pump from here.  I had to replace my old Gast 0523, I bought what appears to be a newer version, the Gast AT05.  Some systems use a different types of pumps, mine used the Gast rotary vane style. The new version the AT05 is fully sealed, which I am a big fan of, and it has a cooling fan.  Septic solutions had it to me the next day, I was pleasantly surprised when it showed up so quickly.  It was my first interaction with them, but apparently I only entered my street number not the road name.  They called within an hour of me placing the order and got the address.  Their speed meant I got to install it over the weekend.  I also grabbed a air line barb and hose clamps to connect the hoses since the septic company who “fixed it” decided electric tape was sufficient for compressed air (it is not).  Make sure you use teflon tape on the fittings for a good seal.

Now for the timer, I did not buy a premade timer I went my own route on this.  I wanted full control over the timer to the minute and it to be cheaper.  Being I have rental house on the same septic I could go from 0-5 people on the system.  Most timers only go down to 15 minutes, two timers was just too complex.  So I went this route:

Custom Timer

This is a digital cycle timer the model I bought was the Inkbird Digital Twin Timer Relay IDT-E2RH.  It lets you set and interval to run and an interval to not run (minimum or 1 sec, max a little over 4 days).  It can do a lot more than that, but that is the purpose I was using it for.  It is Rated for 3A at 240V and 6A at 110V so past the 4.7A draw from my pump.  Also grabbed an enclosure off amazon.  Both items for less than $50 (the price of the analog timer).

The process is then just a matter of cutting a hole in the enclosure for the timer.  Making sure you have some romex cable connectors and spare wire.  You also need to feel comfortable enough to work in a circuit panel yourself.  I moved my timer into the garage where I could see the timer and it was in a dry environment.  I wired the septic breaker into the control box, and the control box to the septic.  Wiring shown in diagram below.



Once it is wired you can give it power.  Mine defaulted to using seconds as the time interval.  You hold in the mode button 3 seconds and the menu gives you some options.  You just hit mode until it gets to the interval screen and switch it from secs to something that kind of looks like “min”.  Hold menu again for 3 seconds.  Then just use the arrows to set A for the time on, hit menu, B for the time off, then menu and you are all set.

Wiring Explained:

  • “NO” means normally off, this is what you will be switching on during the A period.
  • “NC” is normally closed meaning you could switch something on during the off period(B cycle) if you wanted, like I said we are using this device very basically, you can do a lot with it.
  • COM means common, it is what you will be connecting to the NO or NC port depending on the timer completing the circuit.
  • I left the other side alone, We don’t need it for anything in this application.
  • There is also a reset button on the timer, which will restart the timer.
  • It does seem to keep memory in a power outage, not sure for what period, I know at least 30 minutes.

Now when I have renters move in and out I can quickly just change the numbers to the septic system recommendations.  I can also easily see when it should be working and check it.  The pump is sealed, so it should last longer than my previous one.  The timer is now out of the elements now as well.  I really did the timer fo $50 as I had all the basic stuff.  The pump was about $500 but way less than the $1000 my septic guys had said it would run when I originally had it inspected and asked replacement cost.

5 thoughts on “Replacing an Aerobic Septic Timer and Pump

  1. This is a good little timer and you wrote a nice tutorial about how to use it in this application. One thing to note however; it is best practice to switch line voltage (hot) That way, when the device is switched off it is not carrying live voltage. I can send you a schematic want.

    1. That makes a lot of sense. Did it in a hurry and didn’t fully think that through.
      Edit: Just looked, that is actually how I wired it. Just labeled wrong a few days after on my schematic doing it from memory. Will update the image.

  2. Sorry to nitpick but, one other thing that you should address is, you should not run this pump directly off of this control relay. Your reasoning that a 3A rating @ 240V means a 6A rating @ 110V is incorrect. Wire, fuse, relay and almost every electrical component amp ratings remain the same regardless of voltage. Sometimes three phase components will sometimes have a lower amp rating because there are three times the wires/contacts contributing heat, but this is not always the case. My recommendation is that you wire a properly sized thermal overload relay to switch power to your pump. Again, I can send you a schematic if you want.

    1. Whoever did the septic system originally had it set up in this method, I am not expert in this area. How much life could be lost on the pump and what is the opportunity cost of running it all the time vs 25% of the time? I can not find anything in the manual stating it would decrease life when used on a timer? Do you have a source for that?

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