How does a dishwasher know how much water is in it?

The ones I've fixed have a lever sensor which works on air in a pipe pressure they have a pipe from the area where the water collects at the bottom to a sensor which is usually round tucked away higher up in the machine. If the pipe gets blocked the machine over fills and/or doesn't empty correctly. Never seen a sensor fail it is usually a blocked pipe. Same idea in washing machines.

Years ago had such a pipe blocked with soap gunge that caused the washing machine to over-fill. Cleaned out the pipe and all then OK.

That is what I thought I was looking for, but after googling does not seem to be the case.

Time plus flow is volume.

so how does it know when to stop measuring the flow?

It knows when it has turned the flow on and off.

does it drain all the water into that big flat plastic bit at the side?

Dunno, I havent needed to do any work on my Bosch yet.

It does have one major quirk, it can be tricky to get it to start at times and quite often wont do two runs in a row, but does start fine the next day. But just a week ago did

Time multiplied by flow (rate). B-)

Might not need time as such. If the "flow meter" gives an output that coresponds to a given quantity of water having passed through. Say a pulse for each 10 ml. Count 100 pulses and you know that 1 l has passed.

It "knows" how much water it needs...

Washing machine "engineers" call them "pressure switches".

Here is an excellent washing machine "pressure switch" video

I'd have thought there should be a level detector rather than a flow meter, as that would be too hit and miss in my view. One of the reasons I never got one is that so many who do have one have problems with them. In many cases the dishes need pre cleaning or the thing cannot cope so what is the point?Brian

I think the water depth in a dishwasher is not very much compared to a washing machine. Little depth means only a small pressure. I am inclined to agree that a pressure based water level sensor makes more sense, if you have enough depth...

Aye, they don't seem to be the most reliable of machines and there is all the faffing about loading, unloading, powders, rinse aid, salt etc. OK I think you can get "all in one" pods these days but I guess the salt requirement is still there.

And apart from having to pre-clean they send your drinks glasses all "frosted".

I always connect ours to the soft water supply and disconnect the *no salt* service.

Don't put any glass other than Pyrex/empty jars in a dishwasher!

Big Clive has a video tour of the innards of an Indesit washing machine at

He also has a teardown of the ingenious digital sensor at

Excellent simple and informative presentation style. Thanks for the link.

See also recent dishwasher video(s) by the "Technology Connections" youtube channel

Probably difficult to capture the same vibe without Rex ...

More faffing about to maintain that. Not a problem here, lovely soft mains water since they switched the source to Burnhope reservior. No scale in kettle just a little bit of brown deposit that takes months to appear. Previously the supply was from an addit in limestone, that was a little hard, descale kettle once or twice a year of nearly pure white scale. St Albans, hard as nails, descale kettle every couple of months of scale in lots of pretty green and blue colours...

More faffing about hand washing your glasses when you've spnet lots of money an a machine that doesn't do what it's supposed to do...

Thank you. I've often wondered whether they have multiple switches or a transducer to allow for different filling levels.