Troubleshooting 101 for Coffee Technicians: Vetting New Techs


Please overview the knowledge supplied and reply the technical questions under

A double boiler espresso machine is 2 machines in a single.

A steamer (produces steam for steaming milk)

An espresso brewer (pushes water at 193°F by way of espresso floor coffee at 9 bar strain)


The steamer operate is easy. It consists of a tank, 2/three full of water, that’s heated to provide steam that pressurizes the tank. Valves permit steam and/or water to dispense.

Water Stage Management

If water can get low sufficient that the heater components are uncovered, the heater components will expend. To forestall this, a water degree management system is in place.

Water enters the machine from the road out of the exterior pump (extra on the pump later) linked to the water inlet becoming on the correct facet of the machine beneath the drip tray. One department goes by way of an electrically operated valve (the auto fill solenoid) to a one-way (test) valve after which dumps into the highest of the tank (the steam tank is the one behind the machine). A stainless-steel probe (the auto fill probe) is mounted by way of the highest of the tank and, when there may be sufficient water within the unit, it touches the water. This grounds out a low voltage sign coming from the “Water Stage Board” and closes the auto fill solenoid. When the water degree drops, this circuit is not accomplished to floor by way of the water within the tank and the water degree board sends 220VAC voltage to the auto fill solenoid turning it on, permitting water to enter the tank.

Heating Circuit

To get steam you want warmth. Contained in the steam boiler are a number of heater components comparable what you would possibly discover in an ordinary water heater. The heater components run off 220VAC.

Energy from the wall plug enters the machine and is switched on and off by the facility swap on the left entrance of the machine. The swap should be set all the best way clockwise for the heater components to get energy (the primary click on activates the unit’s logic permitting auto fill and testing of brew buttons, however nothing heats). From the facility swap the facility goes by way of a strain swap (the pressurestat, and steadily by way of an over temperature resettable thermal breaker, and into the heater components, heating the water into steam.


The pressurestat is a pressure-operated swap. It’s “usually closed” which means that it begins out within the on place, permitting 220vac to go by way of to the heater components, heating the water. When the water is heated to steam, it builds strain within the tank. A small steam tube connects the steam boiler to the pressurestat. When the steam reaches the preset strain (usually 1.5 bars) the strain turns off the swap off, 220VAC is not capable of attain the heater components, and the water shouldn’t be heated any extra.

When strain drops, the swap is allowed to show again on, heating the water into steam till the purpose is once more reached that turns the swap off once more.

Thermal Breaker (not all models have one)

The thermal breaker is a warmth activated “fuse.” It’s involved with the steam boiler. If one thing goes fallacious, and the steam boiler will get too sizzling, this system will open, stopping the voltage from the pressurestat from attending to the heater components. Urgent down on the button on prime will reset it and permitting the boiler to warmth up as soon as the boiler has cooled. If there’s a fault, inflicting a excessive temp situation, it is going to pop once more until the fault is mounted.

Steam Valves

Two tubes from the highest of the steam boiler go to the left and proper steam valves. These are operated by hand by turning a steam knob counter clockwise to activate the steam, and clockwise to show the steam off.  Many models have further valves mounted between the boiler and the tube to permit the valve to be labored on with out venting the steam from the boiler.

Sizzling Water Valve

Many models have a valve for meting out sizzling water from the boiler for making tea. It may be a guide valve just like the steam valve or it might be a solenoid valve operated by swap. In both case there might be a tube that goes down into the boiler under the water degree so that it’s going to decide up water, not steam.

Handbook Fill

A guide fill button is mounted on the correct facet of the management panel. Its contacts are linked to the auto fill valve. Toggling this swap will activate the auto fill solenoid. That is solely for use when putting in a brand new machine. The on/off swap is ready to the primary click on and the guide fill button is activated as a way to fill the steam boiler for the primary time with out warmth.

Espresso Brewer

The espresso brewer consists of a pump that gives water to the unit at 9 bar strain (a bar is about 13psi) to the “brew boiler” (the tank within the entrance of the machine), a thermostat managed heater to warmth the water, and equipment to carry the coffee and dispense the heated water by way of it. The brew boiler is totally stuffed with water, so no auto fill is required. It’s merely linked to the water supply by way of the pump.


Water from the wall is delivered to the enter facet of an exterior pump. When a shot is known as for (additionally when filling the steam boiler) 220vac is supplied to the pump motor to spice up the water strain to 9 bar. An adjustment screw is supplied to set the right strain. There’s a one-way (test) valve on the output facet of the pump earlier than the hose that connects to the enter facet of the machine.

Heater Circuit

With the on/off swap totally clockwise 220VAC is utilized to the heater components by way of a mechanical thermostat. So long as the water temperature is under the set vary (193°F to 203°F) 220VAC is routed to the heater components. When the right temperature is reached the thermostat shuts off the voltage. There’s a thermal breaker in keeping with the thermostat that may open ought to the thermostat fail and the temperature get too excessive. It resets similar to the one of many steam boiler. There’s a wire from a panel-mounted lamp that goes to the underside of the thermostat. The lamp lights when the boiler is heating.

Brew Management

Giant rocker switches are mounted on the entrance panel of the machine, one for every brew station (brew head). Every swap has four connectors. One set of connectors switches on the 220VAC for the exterior pump to provide the brew strain wanted. The opposite set controls the solenoid valve that runs water by way of the brew head. If you toggle the brew button, each the exterior pump and the brew solenoid for that brew head ought to activate till you turn it again to show them off.

Please reply the questions under.

Machine has energy, however there isn’t any steam strain. Lukewarm water is distributed from the steam wand. Possible trigger? Options?

Brew swap is activated; pump doesn’t have interaction, water does come by way of the group. Possible trigger? Options?

All pump, brew and heating methods function, however espresso is popping out too quick. Possible trigger? Options?

How would you troubleshooting a machine that has an excessive amount of water within the steam boiler?

What part controls voltage to the coffee boiler’s heating component?

What part controls voltage to the steam boiler’s heating component?

There are two electrical cords popping out of the machine. What are every of them for?

What merchandise are distributed from the steam boiler?

Crimson mild on the entrance panel of the machine retains turning on and off, what does that point out?

Clarify how the machine maintains the water degree within 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.]