Tank Overfill Error After Initial Startup in Starbucks Hot/Ambient System

The Mix UC3 / Starbucks Hot/Ambient boiler unit will not operate when the "Tank Overfill" error is displayed.

*Note - this guide will also resolve a slow-to-moderate leak from the ambient dispense on the same model*

Explanation of Error

The error code "Tank Overfill" is the result of water coming into contact with the unit's overflow probe.

The most common cause of this is an improperly closed inlet valve (part number 1502199).

If the inlet valve does not close with a proper seal, water from mains will leak into the tank, slowly filling the unit until the overflow probe is reached. It is very likely that physical debris is preventing a seal within the valve body.

Improperly purged filters and water lines may contain physical debris, which will pass into the valve and cause this problem.

The solution is to clear the valve of this debris.

Resolution of Error

First, resolve the overfill error. This can be done using the drain hose, accessible in the rear of the unit.

Alternately, enter the engineering menu and perform a calibration dispense.

• Press and hold all three buttons on the boiler until a wrench icon and the letters "ENG" are displayed.
• Use PIN 2112 for access to the menu. (DO NOT SHARE THIS PIN WITH STARBUCKS EMPLOYEES)
• Select the dispense calibration and proceed. 

With either option, the goal is to remove water from the tank so that the overfill probe no longer detects water. This will return the unit to operation, but is unlikely to have fully cleared the obstruction in the valve. The error will likely re-occur in the near future.

Full Repair of Issue

These instructions are NOT VALID for units with serial numbers between 0222500721-0222501116 and between 0322500681-0322501041. If you are servicing a unit within these serial ranges, please contact Marco Beverage Systems Support for instructions.

To ensure that the boiler operates properly in the long-term, clear the debris manually:

• Remove the unit from mains power and water.
• Drain the tank of water using the drain hose accessible in the rear of the machine.
• Remove the right side panel of the boiler (as the display faces you).

The valve will be in the lower right-hand corner of the unit as exposed by removing the panel. This is a dual valve: the left valve supplies the tank, and the right valve supplies the ambient water line to the font. 

"Tank Overfill" means the left valve is leaking, and must be opened up and cleared of debris. However, it is advised to clean both valves.

To remove the valves:

• Remove the four wires (two per solenoid) - be sure to make note of which cables lead to which solenoid. Polarity is not important.
• Remove the tubing from the valve body via the quick-connect fittings.
• The valve is secured by a bracket mounted to the chassis. Remove the two screws from beneath the unit.

Yellow cables to the tank fill valve. Green to the ambient valve.

With the valve free of the machine, remove the solenoids from the valve body by prying with a flat-head screwdriver.

With 1+ cm of clearance, you can pull the solenoid manually with minor effort.

The stem is secured behind plastic casing which is threaded into the valve body. Using pliers, gently grip and twist the valve stem until loose enough to unthread by hand. Take care not to mar or score the stem too much that the solenoid will not fit over it.

You have now exposed the valve body. Thoroughly clean out the interior of the valve as well as the mating surface of the plunger. Debris may or may not be obvious, so be thorough.

Note the debris in the valve housing pictured above.

Meanwhile, with the Marco-provided inlet hose (part number 1800693) still connected to mains water but not connected to the unit, purge 5 gallons of water to ensure that the system is clear of any more debris.

Once cleaned, re-assemble the valve. Be sure that the solenoid is fully seated and aligned correctly. It should not be easy to remove without prying if installed correctly.

Next, test that the leak is resolved.

While still removed from the machine, connect the valve to mains water via the purged Marco inlet hose.

With mains water on, watch for leaking at the valve. If the leak persists, repeat the cleaning process.

Otherwise, re-install the valve into the unit and return it to service.

If you have any additional questions or need more information, please email us.support@marcobeveragesystems.com or call 206-641-7677 Monday through Friday from 5am until 5pm Pacific time.