A £3 Part Saved a £700 Dishwasher

The dishwasher stopped mid-cycle, put an inch of grey water in the bottom, and flashed an error the manual translated as "drainage fault — contact service."

A replacement machine is around £700. A service call is £90 before parts. The fault was a component that costs three pounds, and finding it took an evening and a phone torch.

Error codes name the expensive part

This is the thing worth internalising. An appliance error code is not a diagnosis, it is a symptom with a department attached. "Drainage fault" means the machine expected the water level to fall and it did not. Everything in the chain between that expectation and reality is a candidate:

• the pump itself
• the pump's impeller, fouled
• the drain hose, kinked or blocked
• the non-return valve
• the sump filter
• the sensor that reports the water level in the first place

The code points at the first of those because that is the part with an order number. The last one is where the fault actually was.

The float switch

Underneath the machine, in the drip tray, there is a polystyrene float on a short arm sitting over a reed switch. Its only job is to detect a leak: if water collects in the tray, the float rises, the switch trips, and the machine refuses to fill and runs the drain pump continuously to protect your floor.

Mine had been sitting in a slightly damp tray for years in a hard-water area. The float had furred up with limescale and stuck in the raised position. The machine was not failing to drain. The machine believed it was flooded, and was behaving impeccably on that basis — draining forever, refusing to fill, and reporting the only fault code it had for the situation.

The fix, in full

1. Power off at the wall. Genuinely, not standby.
2. Tip the machine backwards onto a towel — the tray is accessible from underneath, no need to pull it out fully.
3. Float lifts straight off its post. Twenty minutes in white vinegar, then a toothbrush.
4. Check the reed switch with a multimeter on continuity while lifting the float by hand. Mine still clicked, so it stayed.
5. Dry the tray, work out where the water in it came from — in my case a perished door seal, £14 — and fix that too, or you are doing this again in a year.

Float cleaned rather than replaced, so the £3 was the seal-adjacent bits and the vinegar. Machine has run a hundred cycles since.

Why I am writing this down

Because the failure mode is generic and it is everywhere. A safety interlock that has failed closed looks exactly like the thing it was protecting against. Washing machines, boilers, tumble dryers, coffee machines — all full of cheap sensors guarding expensive components, and when the cheap sensor sticks, the error code accuses the expensive component.

Before you accept a diagnosis that costs £700, check whether something has merely told a lie for £3.