Indesit Witl-105 Fills With Water Then Shuts Down Mid-Cycle

Nothing needs replacing every few months, the pump filter needs checking (ideally) every several months or so but in practice most people don't need to check it and just clear it if it gets blocked. Read my article on how to deal with a washing machine not emptying water which also contains links to full pump filter guide.

It could be that your washing machine's pump has an intermittent fault, or there's some other intermittent fault causing the issue. Or possibly small obstructions that are either getting flushed out when you drain the machine or even floating back out of the way up the sump hose only to eventually find its way back into the pump again.

Intermittent not draining faults can be tricky to diagnose. When it stops emptying you have to try and assess whether the pump is running, or jammed (often with a gentle humming noise) to get an idea what the problem might be.