A comprehensive guide to common commercial dishwasher issues.
CONTENTS
The following should be used as a guide to help you identify common dishwasher issues and to assess whether it’s a simple fix or whether it needs to be referred to a technician. Quite often issues tend to be something simple so hopefully this information will help you to troubleshoot some so you can at least get through service and avoid a hefty call-out fee.
This is by no means an exhausted list and there are other factors that could fit under each of the following questions.
Some of the smaller issues can be avoided by implementing a proper cleaning and maintenance program. Simple things like ensuring seals are cleaned regularly, removing scale build-up, and checking spray arms and hoses for wear will prolong the life of these components. Regular checks will also alllow you to identify and fix a potential problem before it becomes an issue.
Note that while it’s acceptable to replace some minor parts yourself, there’ll be other components that legally must be carried out by a licensed technician. It’s also worth checking the warranty conditions for any restrictions or specifications with supplies and servicing.
You can download a simplified Dishwasher Troubleshooting Guide Wall Chart here to use as a quick reference guide.
WHY WON’T MY DISHWASHER START?
Power
This sounds like an obvious one but check that the power source is switched on and that the typical lights on the control panel are lit up. Also check the length of the cord for any damage.
If it’s plugged in and there’s no power then there can potentially be an issue with the outlet and not necessarily the machine. You may be able to rule this out by testing another piece of equipment that’s compatible with the outlet or by checking the fuse box.
If the machine has power but the control panel isn’t responding then check the lid in the next step.
Lid/Door and Door Switch
When the door is closed it activates a door switch which lets the machine know it’s safe to start up a cycle. Check that the lid is closing all the way and that nothing is obstructing it. Something as simple as a teaspoon falling off the tray can block it enough to prevent the door switch activating.
Cycle Selector Switch
If your machine has a switch that you physically turn around to select different cycles, make sure that it’s sitting correctly in place. It's an unlikely issue to occur but if it has received a knock and turned slightly it may be sitting in between two different cycle modes and preventing the machine from starting.
Chemical Level
Check that there’s chemical running to the machine. Some dishwasher models are programmed not to start until the correct chemical level is achieved.
Other Potential Issues
Other components that may prevent the machine from starting, amongst other things, are issues with the control board, timer, drive motor, or motor relay. This would require a licensed technician.
WHY WON’T MY DISHWASHER FILL UP?
Water Supply
If water isn’t entering the machine at all then the first thing to check is the water supply to the machine. Check that the valve is turned on and supplying water. Check that the hose hasn’t become disconnected and then check the hose for blockages, kinks, cracks, etc. Check to see if anything is blocking the area where the water enters the machine.
If water is entering the machine but it’s not filling up, first check whether the plug is in place, correctly inserted, and that it’s providing an acceptable seal. Another issue could be that the drain valve hasn't closed properly. Try turning it off and on a couple of times which may help to clear anything obstructing it.
Float
Check the float for damage and ensure that it isn’t stuck or being held down by anything.
Water Inlet Valve
The water inlet valve opens up and shuts off the water flow to the dishwasher. If this fails then there may be inadequate water for a cycle and it may also leak water into the machine when it's off.
Timer
There may be an issue with the timer or setting may have been adjusted.
WHY IS MY DISHWASHER LEAKING?
A leaking dishwasher should be addressed with urgency. Not only will the problem become worse, but it also creates a slip hazard. If it’s ignored and a claim is made then the following months may potentially come with some painful challenges.
There are a number of reasons that may cause a dishwasher to leak. Start by checking the hoses, the seals, and any connections. Hoses will deteriorate over time and develop cracks or damage can occur from pots and trays being dumped next to the machine.
Check the whole machine, not just the area where the leak has been found. Water will travel along surfaces and drip at the lowest point therefore the leak could actually be some distance away from where it appears to be. If it’s difficult to locate you could try emptying the machine and drying it down. Then start it back up while monitoring it closely.
Boilers & Rinse Tanks
The tanks can develop small holes over time which are usually caused by poor cleaning practices. Scale and food soil will build up, and then rust will settle in eventually working its way through the tank. There are ways of patching them up but it’s really just a temporary fix. If rust has formed in one area then it’s likely that other areas will start coming through soon after.
Water is Flowing From the Sides During the Cycle
When the door/lid is closed it activates a door switch allowing the cycle to start, and is switched off upon opening. This happens at the last moment before the door fully closes but this distance can vary slightly between models and the switch may even be activated a couple of centimetres beforehand. In this case, if something gets in the way of the door closing completely it may still appear to be closed properly but there will be a gap just big enough for water to escape through. Check the underneath of the door and also the area the door sits into. It’s also worth checking the hinged part of the handle as something as simple as a tea-towel can restrict it from closing completely.
Seals & O-Rings
Check the condition of the seal around the door. The seal will eventually need replacing as it will deteriorate and water will start escaping as a result.
O-rings are used in a variety of dishwasher components and will also deteriorate over time, requiring a replacement. Some are simple to do yourself and then there’s others that involve dismantling certain parts to access them.
Water Level Sensor or Float Assembly/Switch
The dishwasher will either have a sensor or a float that cuts off the water supply once it reaches the required level. There are different styles and different levels of performance/technology so this may or may not be relevant to you depending on your setup.
SENSOR - The sensor can become soiled or covered in scale which will eventually restrict it from detecting the rise in water level. If this happens the water will continue to run into the machine and overfill because the sensor thinks it’s still empty.
FLOAT – The float rises up with the water and once it reaches the required level it triggers the switch to shut off the water. If the float is obstructed then it may not reach the cut-off point meaning that water will continue to enter the machine. If this appears to be working normally then the issue could be with the switch.
Water Inlet Valve
The water inlet valve opens up and shuts off the water flow to the dishwasher. If this fails then there may be inadequate water for a cycle and it may also leak water into the machine when it's off.
WHY DO MY DISHES COME OUT DIRTY OR WET?
First Consideration
1. Be particular with how items are stacked and loaded into the dishwasher. You want the entire surface of the items cleaned so there shouldn’t be any contact between them and they certainly shouldn’t be stacked on top of each other. Anything that’s baked on or stuck on well will require some scrubbing beforehand and lightly soiled plates and equipment should be given a spray to remove loose food scraps.
Try to load the basket with similar sized items or stack them from smallest to largest otherwise large items can potentially block smaller ones sitting behind them. The wash arms should be able to move freely without interference from the items being washed.
2. Ensure that the chemical dispensing unit is set up properly and dosing the correct amount. The quality and type of chemical will also be a factor and, depending on your particular circumstances, paying an extra $10 for a 5 Litre bottle can be well worth it. Better quality products will provide better results and reduce the amount of items that need to go through a second time. You may even find that it can run with less chemical giving you more washes per litre.
If you’re using a non-chlorinated product and getting inconsistent results then you should notice a difference by swapping it with a chlorinated product. Find out the differences between them here.
A good quality rinse aid will improve the drying process and reduce spotting. The dishes may still come out wet but they should dry within a matter of seconds. Plastics may take a bit longer and it usually helps to give them a quick shake as soon as they come out.
Stopping the cycle before completion will also affect the cleanliness and drying ability.
3. Ensure the dishwashing cycles are set-up correctly according to the manufactures recommendations, particularly regarding temperature, cycle length, and water volume. Then it’s important to maintain the machine with regular thorough cleaning, descaling, and servicing.
A dishwasher that’s in good condition, clean, and working correctly will perform much better than a dirty machine with blocked jets and poorly programmed wash cycles.
Wash and rinse arms should be cleaned regularly as food and scale can clog up the jets and the arms can stiffen up. Make sure that the arms move freely and the jets are free from obstructions.
Filters and trays should be regularly cleaned to remove soils and allow the water to freely pass through them.
Other Potential Issues
Check the wash pump. If it becomes faulty then this will limit how the water cycles through the machine and spray arms.
Check the temperature of the wash and rinse cycles. This should be shown on the control panel otherwise you may need a thermometer of some sort. The wash cycle should be around 65°C and the rinse cycle above 80°C.
If the wash cycle is too high it’s possible, in some cases and to some degree, for soils to actually ‘bake’ onto equipment or plates. If it’s too low then this can reduce the cleaning efficiency. If the rinse cycle is too low then the drying process will be affected and dishes will come out wet and likely stay wet. The sanitation process will also be compromised as it needs to be at high temperatures to kill harmful microbes.
If temperatures can’t be maintained then there may be an issue with the thermostat or heating elements.
WHY IS MY DISHWASHER FOAMING UP EXCESSIVELY?
Excess foam can be caused by:
▹Too much rinse aid in the water.
▹Heavy soil loading in the machine.
▹Not using the correct chemical, or using an incompatible one.
▹Wash temperature too low.
▹Sink dishwashing liquid running into the machine while pre-washing.
Some steps you can take:
▹Check that the correct chemicals are being used and that they’re hooked up to the correct lines.
▹Check that the chemical dispenser is dosing the correct amount of chemical and that the dishwasher is maintaining the correct temperature.
▹Check whether the dishwashing liquid already has a built in rinse aid.
▹Make sure the user isn’t guiding water run-off into the machine.
WHY ISN'T THE DISHWASHER USING ANY CHEMICAL?
The most common issues for chemical not being used come down to blockages or air locks and are simple to fix.
First check whether the chemical dispenser has power. If it has no power and won’t turn on then your best bet is to call an electrician. If it has power then you could check the programming to see if anything has changed, such as the dilution rate, but this might be unlikely.
Tubes on the Chemical Bottle Side
The lines that run from the chemical bottle to the dispenser should be full of chemical. Even if they're half full the air in the tube can create a block. If they are empty then use the ‘Prime’ function to draw the chemical up the line. If the dispenser is trying to draw the chemical up but it’s not working then there’s a few other things you can check.
▹The obvious one is to see if the bottle has run out then replace it and try again.
▹Check that the tubes to the dispenser aren’t back to front. The ones connecting to the chemical bottles should be attached to the side that the dispenser is drawing from and the ones to the dishwasher should be on the side that the dispenser is dosing to.
▹Inspect the whole tube end-to-end for kinks, foreign objects, or splits.
▹Check that the connection to the dispenser is secure and not letting air in.
▹Undo the cap on the chemical. If the tube runs further into the bottle then pull the whole lot out. The end should have a weight attached otherwise it will float on the surface and chemical won’t get in. There also should be a filter on the end although this isn’t essential. If a filter is present then pull it off and try priming again. This will rule out a blocked filter.
▹If you undo the cap and it detaches at the top leaving apiece in the opening of the bottle then this is an encapsulated connection designed for safer handling. Try attaching a different bottle to rule out an issue with the piece inside the chemical.
▹The detergent squeeze tube may need replacing. If the dispenser has a wheel that spins around have a look at the tube that runs over the top of it. Over time this tube will flatten and it'll become difficult for chemical to pass through. If it looks old or flat then this will need replacing.
Tubes on the Dishwasher Side
Similar checks to the above should be made on these tubes as well.
▹Check for any cracks, kinks, blocks, or leaks and make sure that both ends are securely attached.
▹Check the point where the chemical is released into the water for obstructions.
▹Check that the tubes to the dispenser aren’t back to front.
▹Check that the detergent squeeze tube in the dispenser isn't squashed.
WHY ISN’T MY DISHWASHER DRAINING?
The first thing to do is to check the obvious places for blockages.
▹Check to see if anything is obstructing the drain hole in the machine.
▹Check the sump.
▹Check drain hoses for kinks or heavy objects that may be squashing them. These are most likely running behind or underneath the machine.
▹Check the drainage point for obstructions (which may be connected to the sink or running into the wall or on the ground).
▹Check to see that the dishwasher has power. Some dishwashers require power to pump out the water. Has it been switched off accidentally? Has there been a power interruption to the machine?
▹If the machine has a Gravity Waste check that the waste pipe is going straight down out of the machine.
If this isn’t causing the problem then there could be an issue with other components such as the solenoid or timer control, the drain pump, the rinse pump, or impeller.
WHAT IS HARD WATER AND WHAT'S SCALE BUILD UP?
Hard water refers to water that has a high mineral content, particularly calcium and magnesium. Once the water is completely saturated it can’t hold any more calcium carbonate therefore it leaves behind solid mineral deposits.
This is more common in hot environments because the solubility of calcium carbonate in water decreases when the temperature rises and heat also causes evaporation. This means that there will be more calcium carbonate than what the water can take so deposits get left behind.
Over time, the deposits accumulate to forms a crust that we know as scale and constant exposure to hard water leads to scale build up.
If left untreated the scale can cause significant damage to the appliances individual components and the pipes carrying the water. It can lead to corrosion and rust, block waterways and jets, cover heating elements, and seize moving parts. It will form spots on plates and cutlery and cloud glassware which will usually require replacement. Hard water also decreases the efficiency of detergent.
These issues can be controlled with regular cleaning and not allowing the scale to build up. The scale can be difficult to remove but there are chemicals that will make the job easier which is explained further down.
If you’re in an area where scale build up is a big problem then there are water softening systems and filtration units which can be installed to reduce the issue. These can be connected at the machine for the water to pass through before entering the dishwasher or they can be connected at the main water supply to treat the water before entering the building.
HOW TO DESCALE A COMMERCIAL DISHWASHER
The amount of time you leave between cleans really comes down the frequency in which the dishwasher is used and the hardness level of the water entering it. A good rule of thumb is that if there’s scale building up then its probably time to clean it.
Step 1. The Cleaning Product - First you need an acidic cleaning product to dissolve the minerals and there are a number of different chemicals available. Phosphoric acid is commonly used for this purpose as it’s not overly powerful but works well on scale. It can still be quite damaging to the body so follow the recommended handling instructions found in the SDS and on the label.
Step 2. Turn Off the Chemical Dispenser to avoid chemicals being added during the descaling process.
Step 3. Prepare the Machine – The dishwasher will need to be rinsed prior to the clean. This can be done simply by emptying it then refilling it with clean water, remembering that the chemical dispenser should be disconnected at this stage. Run a wash cycle then empty it once it finishes.
Step 4. Descaling the Machine – Refill the machine and add the chemical. Follow the recommended dilution rate on the bottle, or if you’re still unsure it will equate to around 20-30ml of chemical for each litre that the dishwasher holds.
Step 5. Inspect the Machine interior once the cycle has stopped. If there are areas that still have scale attached then you can run another cycle and inspect again. To help the process the remaining scale can be scrubbed with a scourer using a small amount of undiluted/neat chemical. You can continue running wash cycles until you’re happy with the result.
Step 6. Dishwasher Set Up – Empty the machine and rinse as per the instructions in step 3 to remove traces of the acid. Turn the chemical dispenser back on and refill the machine.
SHOULD IT REALLY BE MAKING THAT NOISE?
It’s normal for dishwashers to be noisy during different stages of their cycle and not all dishwashers sound the same. It’s a good idea to become familiar with the noises that your dishwasher makes during normal operation so you can quickly identify anything that doesn’t quite sound right.
An increase in noise or an unfamiliar rattle could mean that something has come loose, bearings have collapsed, a tube has become detached, or a number of other things. Often it may be something as simple as a small item that’s fallen into the machine and moving around when in use.
BE CAREFUL
Although troubleshooting issues yourself will save you money and downtime, if you're really unsure about what you're doing it still may be best to leave it with a technician. That way it’s safer, you won’t risk breaking something else in the process, and it’ll look better from a legal perspective. After all, you're reaching into a square metre space containing water, electricity, and a corrosive chemical.