Hiring a tech and keeping them can be one of the toughest parts of any coffee equipment company’s business. Getting a solid tech and field-trained can cost as much as $20,000 in un-billable time, wages and travel. Therefore, it’s crucial that you have a robust screening process that catches idiosyncrasies, poor communication and other potential red flags before you spend that kind of money.
While the first chapter in this “Troubleshooting 101” series explored brand new systems, this chapter will focus on a diagnostic test for job candidates. The goal of this test is to give a prospective candidate all the information that they may need to troubleshoot simple machine problems. What this tells you, the interviewer, is the candidate’s ability to recall information, troubleshoot, and communicate that back to you.
The questions at the end of the test are meant to be answered by the candidate. This document preceding the questions explains how an espresso machine works. To administer the test, let the prospect read the documentation for 15-30 minutes. Once they feel like they are ready, take the summary document from them and have them answer the questions.
With this type of test, there are no right answers. It’s subjective. Take it yourself and see how well you do. As an evaluator, you are looking for patterns. One pattern I always look for is how long the test takes related to the logic response of the answers. If you have a prospect that takes 10 minutes and half-assed it and the answers did not follow a logical course, you can bet the tech will do the same thing in the field.
Once prospects finish the test, I’ll review the results with them, asking them how they arrived at specific answers. Keep in mind, you are not looking to evaluate the tech for their ability to quickly digest how to repair an espresso machine; you are looking for logical pathways in how the candidate arrived at the solution and how they communicate.
I’ve administered this test on 33 people. My best example of why this test works is a young man who had just graduated from the local university with a degree in film studies. He had no clue what a meter was or how to use it. He took the full half an hour to review and then took about 20 minutes to answer. He got them all wrong. But he clearly communicated how he arrived at his answer and explained his diagnostics. He met the first rule of customer service for me, which is good communication. I hired this kid and trained him for six weeks. He worked for me three years before he moved and went out on his own.
Likewise, I’ve given this to experienced craftsmen. I had a retired gentleman who been a field tech for 30 years. I thought I’d hit the holy grail. He took 15 minutes to review the summary, then 10 minutes to answer the questions. His answers were one or two words and his response to me was a bit glib. I still hired him, but he made it about six moths before I fired him for customer service issue, specifically communication.
Please review the information provided and answer the technical questions below
A double boiler espresso machine is 2 machines in one.
A steamer (produces steam for steaming milk)
An espresso brewer (pushes water at 193°F through espresso ground coffee at 9 bar pressure)
The steamer function is simple. It consists of a tank, 2/3 filled with water, that is heated to produce steam that pressurizes the tank. Valves allow steam and/or water to dispense.
Water Level Control
If water can get low enough that the heater elements are exposed, the heater elements will burn up. To prevent this, a water level control system is in place.
Water enters the machine from the line out of the external pump (more on the pump later) connected to the water inlet fitting on the right side of the machine under the drip tray. One branch goes through an electrically operated valve (the auto fill solenoid) to a one-way (check) valve and then dumps into the top of the tank (the steam tank is the one in the back of the machine). A stainless-steel probe (the auto fill probe) is mounted through the top of the tank and, when there is enough water in the unit, it touches the water. This grounds out a low voltage signal coming from the “Water Level Board” and closes the auto fill solenoid. When the water level drops, this circuit is no longer completed to ground through the water in the tank and the water level board sends 220VAC voltage to the auto fill solenoid turning it on, allowing water to enter the tank.
To get steam you need heat. Inside the steam boiler are one or more heater elements similar what you might find in a standard water heater. The heater elements run off 220VAC.
Power from the wall plug enters the machine and is switched on and off by the power switch on the left front of the machine. The switch must be set all the way clockwise for the heater elements to get power (the first click turns on the unit’s logic allowing auto fill and testing of brew buttons, but nothing heats). From the power switch the power goes through a pressure switch (the pressurestat, and frequently through an over temperature resettable thermal breaker, and into the heater elements, heating the water into steam.
The pressurestat is a pressure-operated switch. It is “normally closed” meaning that it starts out in the on position, allowing 220vac to pass through to the heater elements, heating the water. When the water is heated to steam, it builds pressure in the tank. A small steam tube connects the steam boiler to the pressurestat. When the steam reaches the preset pressure (generally 1.5 bars) the pressure turns off the switch off, 220VAC is no longer able to reach the heater elements, and the water is not heated any more.
When pressure drops, the switch is allowed to turn back on, heating the water into steam until the point is again reached that turns the switch off again.
Thermal Breaker (not all units have one)
The thermal breaker is a heat activated “fuse.” It is in contact with the steam boiler. If something goes wrong, and the steam boiler gets too hot, this device will open, stopping the voltage from the pressurestat from getting to the heater elements. Pressing down on the button on top will reset it and allowing the boiler to heat up once the boiler has cooled. If there is a fault, causing a high temp condition, it will pop again unless the fault is fixed.
Two tubes from the top of the steam boiler go to the left and right steam valves. These are manually operated by turning a steam knob counter clockwise to turn on the steam, and clockwise to turn the steam off. Many units have additional valves mounted between the boiler and the tube to allow the valve to be worked on with out venting the steam from the boiler.
Hot Water Valve
Many units have a valve for dispensing hot water from the boiler for making tea. It can be a manual valve like the steam valve or it may be a solenoid valve operated by an electrical switch. In either case there will be a tube that goes down into the boiler below the water level so that it will pick up water, not steam.
A manual fill button is mounted on the right side of the control panel. Its contacts are connected to the auto fill valve. Toggling this switch will turn on the auto fill solenoid. This is only to be used when installing a new machine. The on/off switch is set to the first click and the manual fill button is activated in order to fill the steam boiler for the first time without heat.
The espresso brewer consists of a pump that provides water to the unit at 9 bar pressure (a bar is about 13psi) to the “brew boiler” (the tank in the front of the machine), a thermostat controlled heater to heat the water, and apparatus to hold the coffee and dispense the heated water through it. The brew boiler is completely full of water, so no auto fill is needed. It is simply connected to the water source through the pump.
Water from the wall is brought to the input side of an external pump. When a shot is called for (also when filling the steam boiler) 220vac is provided to the pump motor to boost the water pressure to 9 bar. An adjustment screw is provided to set the proper pressure. There is a one-way (check) valve on the output side of the pump before the hose that connects to the input side of the machine.
With the on/off switch fully clockwise 220VAC is applied to the heater elements through a mechanical thermostat. As long as the water temperature is below the set range (193°F to 203°F) 220VAC is routed to the heater elements. When the correct temperature is reached the thermostat shuts off the voltage. There is a thermal breaker in line with the thermostat that will open should the thermostat fail and the temperature get too high. It resets just like the one of the steam boiler. There is a wire from a panel-mounted lamp that goes to the bottom of the thermostat. The lamp lights when the boiler is heating.
Large rocker switches are mounted on the front panel of the machine, one for each brew station (brew head). Each switch has 4 connectors. One set of connectors switches on the 220VAC for the external pump to give the brew pressure needed. The other set controls the solenoid valve that runs water through the brew head. When you toggle the brew button, both the external pump and the brew solenoid for that brew head should turn on until you switch it back to turn them off.
Please answer the questions below.
Machine has power, but there is no steam pressure. Lukewarm water is dispensed from the steam wand. Probable cause? Solutions?
Brew switch is activated; pump does not engage, water does come through the group. Probable cause? Solutions?
All pump, brew and heating systems operate, but espresso is coming out too fast. Probable cause? Solutions?
How would you troubleshooting a machine that has too much water in the steam boiler?
What component controls voltage to the coffee boiler’s heating element?
What component controls voltage to the steam boiler’s heating element?
There are two electrical cords coming out of the machine. What are each of them for?
What products are dispensed from the steam boiler?
Red light on the front panel of the machine keeps turning off and on, what does that indicate?
Explain how the machine maintains the water level in the steam boiler.
[Editor’s note: This article is appearing as part of an unpaid editorial collaboration between DCN and the Coffee Technicians Guild. It was originally published in the CTG blog and is republished here with permission. The Coffee Technicians Guild (CTG) is an official trade guild of the Specialty Coffee Association (SCA) dedicated to supporting the coffee industry through the development of professional technicians.]