Fault Finding on a Dishwasher

Before doing anything with any electrical appliance, especially a large item such as a dishwasher, you must ensure it is disconnected from the mains power supply. It may sound a simple thing to do but too many serious accidents occur every year because someone has forgotten to turn it off, or assumed someone else had already disconnected the supply.

Dishwashers are far more complex than many people realise. It is generally thought a dishwasher is much more simple than a washing machine, but there are probably as many moving parts in a dishwasher, and they are all capable of going wrong!

Common Dishwasher Problems

Won’t start:

First thing to check is the electrical supply. You should also check both the fuse and the wiring in the plug itself. If this doesn’t work, try plugging another appliance into the same socket. If there is no issue with either the plug or the socket, you will need to locate and check the mains filter, similar to a capacitor with extra terminals. Ensure you discharge any remaining power prior to testing.

Below is set out a list of points to check:

Plug, socket and fuse
Mains cable and terminal block
Mains filter
Door wiring
Main on/off switch
PCB or timer

If all the above is unsuccessful you may have no option but call in an engineer to resolve the problem.

Lights flash and/or machine won’t start:

Along with washing machines, many manufacturers of modern dishwashers will have a system that will stop the machine from working if any fault is detected. These error codes are generally meaningless, other than to flag there is a problem.

Unfortunately, you will have to systematically work through possible faults; the Troubleshooting section of your manufacturer’s handbook may give you a good starting point. Hopefully you can resolve this issue without the need to call in an engineer.

Dishwasher noisy:

Without knowing what type of noise and when in the cycle it occurs, it is difficult to diagnose a problem. Things to check would include:

Spray arms are correctly fitted, or the mounts are faulty
Main recirculation motor
Drain pump faulty
Drain pump jammed or object trapped
Object in main recirculation impeller housing

Won’t drain or empty water:

This will indicate either a fault with the pump or the house plumbing. Try working through the following suggestions:

Drain pump faulty
Drain pump jammed or object trapped
Object in the main recirculation impeller housing
Main recirculation motor

Dishwasher won’t wash:

Generally this means that the spray arms are either not turning, or not turning well enough to really clean the dishes. This can be caused by many things, dependent on both the make and model of the dishwasher.

Where there is a capacitor for the motor on the affected model, it will mean the capacitor is faulty and the motor is not running strongly or at the correct speed. On other machines, the problem could be caused by a split tube that feeds water to the spray arms.

The most probable cause is the main recirculation motor with either the capacitor faulty, or the main pump impeller jammed or broken.

Spray arms blocked
Pressure loss
Tube split
Motor capacitor faulty
Main recirculation motor impeller jammed or faulty
Main recirculation motor faulty

Poor results:

The best place to look is the filters – you will need to remove them from the bottom of the machine, clean thoroughly and make sure there is no debris blocking the hose located behind the filter.

Are you using the best detergent you can – if you are using solid tablets the volume of water for each cycle may not be enough to fully dissolve the tablet, giving incorrect cleaning power and leaving residue inside the soap compartment, or ending up blocking the filter.

Also, are you using a rinse aid product, this is essential to keep the machine working to its best standard. Do you regularly top up the dishwasher salt? This is also essential to keep the machine working to its best. Most machines will flash an indicator light to let you know when more salt or rinse aid is required.

Water leaking from the door:

This could indicate the door seal needs to be replaced. Another reason could be a split spray arm – these are only made from plastic and can fail. A split arm could cause the water to spray in the wrong direction, causing the leak from the door. Spare parts should be easily obtainable, but make sure you have the full make, model and serial number to have the correct parts.

However, if you have not identified the cause, the following list should help:

Spray arm split or faulty
Door seal damage, both lower and goalpost seal or gasket
Overfilling
Correct detergent use – too much can cause overfoaming

Leaking from underneath:

This can be really difficult to narrow down, but common causes are:

Pump faulty, leaking
Main recirculation motor seal leaking
Hose failure
Sump seal
Regeneration chamber
Overfilling
Incorrect detergent use causing overfoaming

Catches fire!

Don’t worry, this is a much rarer occurrence than in the past. It is highly unlikely that you will ever see flames from your machine, but you may see a puff of smoke or smell of burning following an electrical component burn out.

Turn off the power first, and let the machine cool right down before you start investigating further. If a component has burnt out it should be very easy to spot. If you are uncomfortable with this, you may feel better if you call in an engineer.

Water not filling into the machine:

If error codes are not flashing, it is very likely to be a faulty inlet valve. These are reasonably easy to replace, although be aware some will have a pressure switch attached, in which case you may decide to call in an engineer.

Disclaimer: The information provided has been prepared as a guide only and the steps taken are likely to vary for different appliance models. We strongly recommend using a qualified engineer to undertake major repairs and fault finding.