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How to Descale a Rational Combi Oven

Rational service technician

Descaling combination ovens are crucial for maintaining proper operation. When conducting preventative maintenance on a Rational unit, following the right procedure is a must. Below are materials and instructions for how to descale a Rational combi oven.

WARNING: Since combi cleaning solutions are made of aggressive chemicals, there is a risk of chemical burns to the skin or eyes. Be sure to always wear protective clothing, gloves and safety goggles or a facemask throughout the descaling procedure. Make sure to follow instructions and safety notes on the chemical’s label and the descaler pump.

Supplies

Below is a list of cleaning accessories and safety gear that Rational requires:

Descaling a CombiMaster Plus®

Rational CMP 101 E

Below is the descaling procedure that Rational requires for a CombiMaster Plus (2011-present). These instructions are for authorized service technicians only:

Step 1. Turn the top control mode knob to the “Cool Down” function at the bottom.

Step 2. Close the cabinet doors. Make sure each door sealed shut.

Step 3. Press the Core Temperature button down for 10 seconds. Wait until the cabinet temperature display reads “CLEn.”

Step 4. Turn the temperature knob in the middle to the right. Wait until “CALC” appears on the cabinet temperature display.

Step 5. Press the clock button near the time/core temperature display. The descaling process will begin. You’ll notice the following:

  • After the steam generator drains, the cabinet temperature display will show four dashes.
  • After the oven has finished pumping out, the cabinet temperature display will show “CALC” and the time/core temperature display will show “FILL.” Top off the machine with the descaling chemical.

Step 6. Following the procedures in step 5, open the cabinet doors.

Step 7. Remove the left grid shelf and air baffle from the interior cabinet.

Step 8. Guide the hose into the opening of the steam inlet as far as the mark. Follow the instructions on the descaler pump.

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Step 9. Place the hanging rack and fix hose inside the cabinet with wire hooks.

Step 10. Place the descaling chemical container in the cabinet. Run the hose into the container opening.

Step 11. Slowly fill with descaling fluid. Be aware that the chemical reacts with lime, causing it to foam over. Below is how much descaler should be applied per unit:

  • 6 x 1/1 GN = 3.5 liters/0.924 gallons (electric), 4 liters/1.06 gallons (gas)
  • 10 x 1/1 GN = 6 liters/1.59 gallons (electric), 7 liters/1.85 gallons (gas)
  • 6 x 2/1 GN = 6 liters/1.59 gallons (electric), 6.5 liters/1.72 gallons (gas)
  • 10 x 2/1 GN = 8.5 liters/2.25 gallons (electric), 9 liters/2.37 gallons (gas)
  • 20 x 1/1 GN = 9 liters/2.37 gallons (electric), 8 liters/2.11 gallons (gas)
  • 20 x 2/1 GN = 11.5 (electric)/3.04 gallons, 11 liters/2.91 gallons (gas)

Step 12. When you’re finished spraying, remove the chemical container and pump from the cabinet.

Step 13. Rinse the cooking cabinet thoroughly with water to remove any descaling chemicals. Also, rinse the hanging rack and wire hooks.

Step 14. Insert the air baffle and left grid shelf. Make sure they’re locked firmly into place.

Step 15. Set the clock to 30 seconds. After 30 seconds, “Door” will appear on the time/core temperature display.

Step 16. Close the cooking cabinet doors. The following will occur:

  • The length of the descaling phase will appear on the cabinet temperature display.
  • The machine automatically rinses out the descaling chemical several times before automatically switching to “Steam” mode. The time for both procedures appears on the time/core temperature display.
  • When the time/core temperature display shows “End,” that means descaling is complete.

Step 17. Exit the descaling procedure by turning the top control mode knob to a cooking mode.

View the full procedure and more tips from this Rational manual.

Descaling a SelfCookingCenter®

Rational SCC WE 61E Combi Oven

Below is the manual descaling procedure that Rational requires for a SelfCookingCenter (2008-present). These instructions are for authorized service technicians only:

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Steam Generator Instructions

Step 1. Start the descaling procedure on the touchscreen by:

  • Pressing the “Function” button
  • Pressing the “Technik” button
  • Selecting “Descaling”

Step 2. Activate Cool Down mode if the oven is more than 75 degrees Celsius (167 degrees Fahrenheit). The oven’s display with show “Unit too hot.” If doesn’t, proceed to step 3. Below is how to start Cool Down mode:

  • Select cooking mode.
  • Press the “Cool Down” button and close the cooking cabinet door.
  • When prompted with “Open door,” open the cabinet door.
  • The current cooking temperature will display along with the word “Cool Down.”
  • Close the cabinet door to proceed to step 3.

Step 3. Wait for the steam generator to drain. The screen will display “wait steam generator cooling.”

Step 4. Open the cooking cabinet door to remove the left hanging rack and air baffle.

Step 5. Guide the hose into the opening of the steam inlet as far as the mark. Follow the instructions on the descaler pump.  

Step 7. Place the hanging rack and fix hose inside the cabinet with wire hooks.

Step 8. Place the descaling chemical container in the cabinet. Run the hose into the container opening.

Step 9. Slowly fill with descaling fluid indicated on the display screen. Be aware that the chemical reacts with lime, causing it to foam over.

Step 10. Remove the descaling container, pump and other accessories. Then, insert air baffle and left hanging rack. Lock both firmly into place.

Step 11. Press the “finish filling” button on the screen to drain the unit. A clock will display and the oven will automatically fill and drain the machine.

Step 12. When the clock hits “0:00,” press the “Back” arrow button to end the procedure.

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Humidifying/Moistening Nozzle Instructions

Step 1. Turn the unit off.

Step 2. Remove the left hanging rack from inside the cooking cabinet.

Step 3. Open the air baffle. Then, unfasten the union nut on the humidifying nozzle by turning it counterclockwise.

Step 4.  Remove the humidifying nozzle and place it in descaling chemical. Let it soak until it’s scale-free.

Step 5. Reinstall the nozzle following the disassembly in reverse order.

Step 6. Close the air baffle and reinstall the left hanging rack. Make sure the rack is locked firmly into place.

View the full procedure and more tips from this Rational manual.

Tips from an Expert

One of our top members, Ectofix, provided some great insight into the descaling process for a SelfCookingCenter Combi. Here are some valuable tips he provided for techs to remember when descaling an especially dirty combi:

1. The descaler should ONLY be put into the boiler through the steam port inside the oven’s cooking compartment by using a pump.
2. If you spill any descaler…or if it comes bubbling out of the steam port from chemical reaction, thoroughly rinse out the cooking compartment with hand shower.
3. Make ABSOLUTELY sure that the SC pump works BEFORE beginning, since that’s the primary means to remove the descaling solution.
4. Once the descaling solution is out – flush, FLUSH and FLUSH – with clean water via function testing of the FILL valve.

Ectofix

1. OVERFILL the boiler until it’s running down into the floor drain…all three times. 
2. Fill a forth time and run in steam mode for fifteen minutes. 
3. Follow that by function-testing the fill valve again, letting the overflow run into the floor drain for awhile. 
4. The idea here is to “temper” the water before function-testing the SC pump, thereby not making the pump work with boiling hot water – to avoid damaging it.
5. Run the SC pump to drain the boiler one last time.
6. Thoroughly rinse the cooking compartment one last time with the hand shower.

Ectofix

Check out the full post here.

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