Water pouring out of a washing machine's detergent tray.

[EC8010]

Yes, gentle reader, I have spent time on a Sunday with my arms deep inside a washing machine. I received a panicked telephone call at 22:30 on Thursday to report that water was pouring out of the detergent tray all over the kitchen floor. I've seen this one before, so let me share the knowledge with you...

The drum spins inside a fixed drum. Towards the bottom of the fixed drum is a 1/4" (6mm) internal diameter pipe leading to a sensor mounted near the top of the machine, with wires to the control circuitry. This is the water level sensor. The rising water applies pressure to the air in the pipe and this acts upon a diaphragm in the sensor that actuates a microswitch and operates the solenoid valve to switch off the incoming water.

Alternatively, the sensor fails, the water level rises until the drum fills with water and it overflows out the front of the detergent tray.

But that's unlikely. What's far more likely is that the pipe becomes blocked and that prevents the water being switched off. The pipe pushes onto a sprue on the drum and that's where it gets blocked. Pull the pipe off and use a bit of bicycle brake cable to clear the blockage and reassemble. You can check the sensor by removing it and using the continuity test on your meter whilst blowing into it.

This fix worked ten years ago on my Hoover and today on a Bosch. No need to spend money, just fix it yourself...

[SY]

Just curious, did you spay your cats yourself?

[Eva]

Very true. Some models are very prone to getting the pipe going to the pressure switch clogged with rests of detergent and fibres of clothes. Others are very unlikely to produce that failure, though. It's more of a design flaw.

Anyway, if the water outtake pipe had been plugged to an outlet at a proper height, water would have never been spilled. Optimum height is slightly above the maximum drum water level, which is achieved during rinsing. Any higher level would be spilled through the outtake pipe. Note that the pressure sensor usually has two, three or four contacts in order to achieve several water levels for different programs.

Well, that is only valid for "old style" washing machines as I have not had the chance to repair any "new generation" one, but I suppose that they are now employing analog water level sensors and a microcontroller in order to achieve water saving (not to mention DC motors with electronically controlled torque and speed instead of the old school heavy synchronous ones).

[EC8010]

No, the cats came pre-spayed as part of the cattery conditions of adoption.

Yes, the water sensor blockage thing is a design flaw, but I don't see that the height of the waste pipe final plumbing makes any difference. The waste pipe exits from the top of the washing machine, and as it can't remain full of water and siphon, overfilling the machine will always cause water to come out of whichever is lower. It's a close run thing between the tray and the pipe exit, so perhaps water exited by both. but as the waste pipe's plumbed into the sink trap, it couldn't be seen.

[Eva]

Ops... Thats another design flaw. The waste pipe should exit from the bottom or from the middle in order to allow for siphon effect to happen during overfilling.

[pinkmouse]

Nope, design feature, it stops dirty water being sucked back into the machine during rinse cycles.

[Eva]

No water is ever sucked into the machine through the waste pipe. The pump always empties the drum before the next rinse cycle starts. Could you explain further?

[Netlist]

From a washing machine tech:
It’s more complicated than that; some machines have the pipe mounted at the bottom.
The drawback is that if the pipe, when accidentally falling on the ground or mounted too low, empties the machine if filled with water.
Other machines have the pipe mounted on top and sometimes come with a small pipe parallel to the big one. These pipes can be mounted on floor level without risk for the machine to siphon.
The small pipe is actually filled with air but the exact principle escapes me.
Those without the small pipe should be mounted high enough from the floor level to prevent siphoning as well.
A second tech told me that the pipe is always mounted on top because a siphon is built in the machine to prevent it from smelling. I don’t consider this as correct. Actually, it wasn’t a tech but a salesman.

/Hugo

[Eva]

Indeed, having the waste pipe exiting from the bottom can cause all the water to spill if the pipe is dropped from the waste outlet to the floor. However, believe me that it (siphoning) comes very handy when you have to manually empty the drum when the pump or something else fails, or when you want to clean the waste filter without filling the floor with the small remaining amount of water that the pump can't exhaust.

I know because my grandfather spent a whole life repairing washing machines (among much other stuff) and I used to go all the time with him when I was a child. It was funny because he always asked me for a diagnose before starting to work

[EC8010]

Originally posted by Eva
No water is ever sucked into the machine through the waste pipe. The pump always empties the drum before the next rinse cycle starts. Could you explain further?

Agreed, the machine isn't designed to suck water into the machine via the waste pipe, but if the pipe was full of water and able to siphon, then emptying a full sink would send dirty sink water into the machine because modern practice is to connect the washing machine waste to the sink waste just above the trap.

I should have known that on diyAudio an innocent post about a washing machine fault would provoke a spirited discussion of how washing machines work!