SOLVED: Why is my commercial dishwasher not draining?

Advanced Chemical Solutions
July 26, 2022
5 min read


Before we dive into specifics, let's cover some general checks that are easily identifiable. A commercial dishwasher for a restaurant will experience high volumes of traffic and are built to do so. This increases the chances of drainage obstructions or electrical faults. Examine your dishwasher, visually and audibly. 

  • Inspect water flow, the drain hose, and the Drain Pump. Replace your drain hose using a reinforced steel-braided material every five years regardless of wear. 
  • Check the cycle process, listen to the machine, has it stopped mid-cycle?
  • Inspect your machine's power source – does your dishwasher have power, or has the cycle been interrupted due to a power outage?


There are two methods a commercial dishwasher removes wastewater. A Gravity Drain relies on nature's gravity to remove dirty water from the machine's wash tank. This type of drainage requires the drainpipe to be the lowest part of the dishmachine. Most commonly, by placing the dish machine on a counter or stand.

The second method includes a Drain Pump. Your dishmachine will need a drain pump if the outlet is higher than the drain level. At the end of a wash cycle, the pump will automatically remove wastewater from the tank and down the drain. Issues include blockages, collapsed bearings, clogs, and kinks, or other obstructions that can hinder your machine's ability to release water.

Clear your lines and check for blockages. A rouge piece of food or glass can be a common culprit.

ACTION: Test your Drain Pump by running a drain function. While listening to the pump, visually check to see if the pump is pulling water out. If not, you may have a bad pump that will need to be replaced.


ISSUE: An Impeller is a mechanical device made of durable plastic, nylon, or metal. This device uses its rotation to create a sucking force. Damage and wear from foreign objects such as paper clips will cause direct issues to your draining performance. ACTION: Check your machine's impeller for wear or restricted movement.

Commercial dishwasher CMA impeller device


ISSUE: During various stages of the cleaning cycle, water pumps perform essential tasks responsible for pulling and removing water. Over time, that continual operation can lead to wear and eventual failure. Listen to the performance of your machine at the end of a wash cycle. Are there strange noises? Inability to drain properly and abnormal noises are a sign of collapsed pump bearings.

ACTION: At this point, it is best to replace the pump itself.


ISSUE: The timer control is responsible for sending an electrical current during the drain cycle to the drain solenoid, triggering the solenoid to open the drain valve and release water. An error in this transition from electrical function to mechanical action can result in drainage issues.

Hobart AM15 Drain Solenoid

ACTION: If the valve fails to open, water will fail to drain from the machine. Test your solenoid by using a multimeter to check for resistance. Connecting to the terminals, your reading should change from infinity to approximately forty ohms.

A drain solenoid is a common and easy part to replace. Have a service rep examine the issue and test any other electrical errors that may persist.


Check out this complete troubleshooting guide for operating a Hobart dishwasher. For popular models such as AM, CLe, C-Line, LXe, and LXi series.