Dishwasher Not Draining Or Leaving Dishes Dirty

What's happening?

These two complaints share a cause more often than people expect, because both come down to water moving properly. A dishwasher fills, recirculates through the spray arms, then pumps out through the drain hose to the waste. Standing water at the end means the drain side has failed: the filter, the drain pump, the hose, or the waste connection it discharges into — very often the sink trap spigot, still blanked or half blocked. Poor cleaning means the wash side is not working: blocked spray arm jets, a clogged filter recirculating debris, a full salt or rinse aid reservoir left empty in a hard water area, or overloading so the arms cannot turn. A dishwasher that has stood unused, or is drained through a badly routed hose, gets both problems at once.

What usually causes it?

• A blocked filter and sump in the base, packed with food debris, glass chips and labels
• A blocked or badly routed drain hose, or one with no high loop, allowing waste to siphon back
• A blanked or partly blocked spigot on the sink trap the dishwasher drains into
• A blocked kitchen sink waste or trap, so the dishwasher has nowhere to discharge
• Blocked spray arm jets, limescaled or full of debris, so the arms do not clean or turn freely
• A failed drain pump, or something jammed in the impeller
• Empty salt and rinse aid reservoirs in a hard water area, giving cloudy, gritty results
• Overloading and poor stacking, so items block the arms and shield each other from the spray

When should you call an appliance repair engineer?

Call an appliance engineer when the filter, spray arms, hose and waste are all clear and it still will not drain, which points at the drain pump or the control board. Call if the pump makes no noise at the drain stage or hums without shifting water, if the machine leaks as well as failing to drain, or if it trips the electrics. A built-in machine has to come out to be worked on, and getting it out past a fitted plinth and a stone worktop is part of the job.

What will the appliance repair engineer actually do?

• Read the fault code, then drain the machine down and inspect the filter, sump and drain pump impeller
• Test the drain pump for continuity and running current to separate seized from failed
• Check the drain hose routing, high loop and the household waste connection rather than only the appliance
• Test the inlet valve, circulation pump and spray arm pressure where cleaning is the complaint
• Check the heater and thermostat, since a machine washing cold cleans poorly whatever else is right
• Withdraw and refit the machine safely under a fitted worktop, then run a full cycle and check for leaks