Auto Refill Circuits & How They Work
by Terry Ziniewicz

Espresso Machines truly are modern day miracles. The simple fact that you can plug in this large electro/hydraulic machine and have it brew coffee is amazing and the fact that it will do it time and again is truly a miracle and a statement to those engineers who have developed the technology. To most barista and bar owners the internal workings of an espresso machine are a mystery. Simple maintenance of these mysteries can be important to the longevity of the machine. The continued purpose of this column is to help demystify the internal workings of an espresso machine and this month we will look at the mystery of how the darn thing stays full of water.

Water... no big mystery here. Every espresso machine requires water and as long as your machine is connected to water its going to work. Making sure that the water gets into the boiler is the function of the auto refill circuit. You use your espresso machine every day, and for hours all day long, you pull shots and they just keep coming out, no problem, right? Well fact is that unless your machine has a proper water supply your machine could have a major malfunction. Good clean quality water is a major factor in how well your espresso machine performs and even the cleanest water will still have minerals that attach themselves to the inner workings of your espresso machine.

The auto refill function of your espresso machine is an important function that most operators are not even aware exists, nor do they care to be bothered by its existence. But bothered is just part of how you feel if it don't work. Imagine, your at home at night and your machine replaces its water level automatically! The next day you pull a shot or ten and the Boiler water level stays the same. Yep, its a miracle and to keep this miracle occurring you need to understand how works the auto refill function. This is all completed by a electronic water control unit that tells the water pump to come on and to stop at a pre determined level. Most all machines use this device to fill the boiler. Even most Lever equipment relies on this method of water level control. A major component of this process is the auto refill probe. The auto refill probe is most often the culprit in many espresso machine catastrophes. Lack of attention to this one component can cost you hundreds in repairs. Depending on how the machine reacts to a dirty refill probe will determine the type of catastrophe you will have. If the machine decides to overfill you have what we call a good catastrophe if it decides to not fill at all , well that another story. In most cases if the boiler does not refill the heating element burns out or disintegrates inside the boiler, and well I think you get the picture.

To locate the auto refill probe on your espresso machine, turn off the power and release all steam pressure Via the steam wands. Remove top panels of your machine to reveal the boiler (some machines require the removal of a cup heating device to remove top panels). With the boiler in plain view look for a single wire attached to a stainless steel probe about the diameter of a pencil lead, on some machines it is located in the top of the sight glass assembly or on the top or side of the boiler.

Once you have located the probe, note the location of the probe with regards to its height and angle from the top or side of the boiler or sight glass this will ensure that your machine fills to the correct level upon replacement. Remove the wire and loosen the top nut of the probe assembly this will allow you to remove them probe from the boiler or sight glass. As you remove the probe the viton or Teflon sleeve that surrounds the probe will also come out. After removal you may see mineral scale build up on the end of the probe, this is the cause of refill failure if the probe cannot detect water the pump will either not shut off, causing the boiler to overfill or not come on causing, yep, the worst case catastrophe, element melt down. Removing the scale is as easy as sanding the probe with some emery cloth or use a small file to clean its surface. Once you've removed all traces of mineral scale, replace the probe and tighten the top nut. Reattach the wire to the probe. Remember to reset the probe at the same height and or angle that it was prior to removal. Now restore power to the machine. When you first turn the machine on you can will hear the pump auto start and autofill the boiler to the predetermined level. To test the your work and to ensure that the machine is autofilling, remove the wire attached to the probe, the pump motor should come on, when it does, return the wire to the probe, the pump should now shut off. If performing this type of maintenance is just not your thing and you could care less about how it all works, just ask your local espresso machine technician to complete this task for you. Mineral scale will always be the main cause of early failure in an espresso machine . What you do to reduce its effects now, will pay off in the future.

Reducing this type of mineral created damage with the use of a water filter system and or a water softener is really the best you can do. To ensure that mineral scale is not effecting the internal workings of your machine, you should test the auto fill function every time you change group gaskets or every 3 months. With a little maintenance on these mystery functions of your espresso equipment, you can save hours of downtime and a ton of money. Next month we will delve into the mystery of that thing you put the coffee in "The portafilter" stay tuned..