Dehumidifier on continuous mode keeps filling its tank and stopping, even though the room never feels damp — why?

Two litres a day is unremarkable, and the reason it does not feel humid is that humidity is a percentage, not a quantity.

A moderately sized room holds a surprising amount of water in the air, and more keeps arriving: people breathe out roughly a litre a day each, showers and cooking add several, drying laundry indoors adds a couple of litres per load, and in a cold house moisture moves in from unheated rooms and from the fabric of the building itself.

The machine is not emptying a reservoir — it is intercepting a flow. It will keep collecting for as long as moisture keeps arriving, which is forever. That is not a fault and it is not evidence the room was unusually wet.

Also worth knowing: a room at a comfortable 50% relative humidity still has a lot of extractable water in it. "Does not feel damp" and "nothing to collect" are different statements.

Continuous mode means it ignores the humidity target, not that it ignores the tank. The float switch that stops it when the tank is full is a safety and it always applies.

So the behaviour you are seeing — runs, fills, stops — is exactly what continuous mode does when the tank is not being emptied.

The fix for that is the part nobody mentions in the shop: almost every dehumidifier has a drain hose outlet, usually a small blanked spigot at the back. Fit a hose, run it to a sink, a drain, or out through an airbrick, and the tank stops being the limit. That is what continuous mode is designed to be used with.

Without the hose, continuous mode is close to pointless — you have swapped an automatic machine for one that needs you twice a day.

On question 3, whether it is useful: stop using continuous mode and set a target instead, and it will be.

Continuous runs the compressor whether or not the air needs drying, which is where the bill comes from. Set it to a humidity target — somewhere around 50-55% is the usual advice for comfort and for keeping condensation off the glass — and it cycles on only when the room drifts above that.

The useful outcome is not a dry room. It is a room where the windows stop streaming and the corners stop growing mould, and that happens well before the air feels dry.

Worth doing at the same time: find where the moisture is entering. A dehumidifier fighting laundry dried on a radiator every day is doing the work an open window and ten minutes would do for free.