Miele WEG365 WCS: drain fault and pump cavitation after transport - looking for W1/PowerWash expertise

What you have observed does point more towards a hydraulic issue than a simple seized pump, especially if slightly breaking the filter seal immediately changes the noise. On these Miele W1/PowerWash machines, it is quite possible for a pump to spin freely by hand but still fail under load, or to become noisy if it is being starved, air-locked, or pulling against a restriction.

1. First, treat the two pumps separately. On many Miele W1 PowerWash models there is a drain pump and a separate circulation pump for the PowerWash recirculation system. The filter access at the front is usually associated with the drain system, but on some versions the twin access points relate to a shared housing arrangement. Without the exploded diagram for your exact product number, I would not want to guess which side is which. The safest next step is to identify parts by your full model and product number in the Whitegoods Help Spare Parts Shop, then compare the pump and filter housing layout.

2. Check the sump hose from outer tub to pump housing. Yes, many washers use a ball, flap, or restriction device in this hose, and if it has shifted, stuck, or become obstructed after transport it could cause starvation and the sort of cavitation noise you describe. Isolate from the mains first, then inspect the full hose internally, not just the filter chambers.

3. Inspect for partial air leaks on the suction side. A poor seal around the filter cap, pump housing, or hose joint can let air in without always leaking much water out. Your “seal broken, noise changes” finding makes this worth checking carefully.

4. Check the pressure chamber and any small vent or sensing passages off the sump. A blockage there is less likely to directly cause cavitation, but it can confuse water level sensing and cause odd drain behaviour.

5. Do not rule out a weak pump. A damaged impeller, split magnet, or worn pump can behave normally by hand yet lose performance when moving water.

6. If you can access service mode, use it only to run individual pump functions briefly and listen for which pump is making the noise. If you are not certain of the procedure, it is better not to force tests blindly.

Before replacing parts, I would inspect the tub-to-sump hose, pump housing inlet, seals, and any non-return device first. If you need parts or diagrams, search the Whitegoods Help Spare Parts Shop by the full model number and product number. For any mains-related testing or internal electrical work, and for anything you are not confident stripping down, use a qualified appliance engineer.

WhitegoodsHelp AI Assistant

You may also find this guide on our main site helpful: "Rattling Tapping Grinding Noise in Spin" - https://www.whitegoodshelp.co.uk/tapping-grinding-noise-on-spin/

Hi Phil,

Your reasoning is sound, and the detail about the noise stopping the moment you cracked the right-hand filter seal is the most useful thing in your post. Answers to your questions below, based on our engineers’ experience with the W1 PowerWash range, including one who worked for Miele UK.

1. Which filter is which

Looking at the machine from the front, the left-hand filter is the drain pump and the right-hand filter is the PowerWash circulation pump. The two pumps sit on a shared filter housing. You can confirm it on your own machine without guessing: the drain pump is the one whose outlet hose runs to the back of the machine and out to the waste, while the circulation pump’s outlet hose runs back up towards the tub to feed the PowerWash nozzle.

One warning if you end up ordering a pump. The exploded parts drawing for this housing shows the two pumps the wrong way round. Order by part number and by the hose routing described above, not by where the pump sits on the drawing, or you’ll get the wrong one.

2. The sump hose

Yes. The hose from the outer tub down to the pump housing contains a ball, and there’s a lid seal where it meets the housing. Both block easily with lint, hair and small items, and either can restrict the inlet enough to starve the pump. This is the first thing to inspect and the most likely cause of what you’re hearing.

3. Vent or air-balancing passage

There isn’t one to worry about on this layout. Don’t spend time looking for it.

4. Transport

This isn’t a known transport fault and the hose, ball and housing don’t shift during a move. What a move does do is tip the machine, and anything sitting harmlessly in the sump beforehand can end up in the ball seat or the hose. So the move is probably the trigger, but the cause will be a foreign object or debris, not something that has moved out of position.

5. Why the seal test points at the inlet, not the pump

On Drain/Spin only the drain pump should be running, so the noise is coming from the left-hand pump even though you cracked the right-hand seal. Because the housing is shared, opening the right-hand seal let air into the housing and relieved the suction the drain pump was pulling against. A pump that goes quiet the instant its inlet is relieved is being starved. A pump with a mechanical fault would carry on rattling.

6. Can a pump spin freely by hand but fail under load

Yes, it can. A tired motor or a damaged impeller hub can feel fine by hand and still fail once it’s moving water. But don’t replace either pump yet. The evidence you already have points at the inlet side.

7. What to check next, in order

- Isolate the machine from the mains and drain it fully through the filters. - Remove the sump hose from the outer tub and the pump housing. Check the ball moves freely, its seat is clear, the lid seal is intact and seated, and there’s nothing in the bore of the hose. - Check the inlet of the pump housing where the hose connects for anything lodged there. - Check both filter caps and their seals. A cap that isn’t fully home, or a seal that’s nicked or sitting badly, can let air into the housing without leaking much water, and that alone can cause what you’re hearing. - Refit everything, put the machine on a tray, run Drain/Spin with a few litres of water in the drum and listen at the left-hand filter. - Only if it’s still cavitating with a clean inlet and good seals should you suspect the drain pump itself.

8. Service mode

There is a Miele diagnostic mode that lets an engineer run the drain pump and the circulation pump individually. It’s a manufacturer service procedure, the entry sequence varies by model, and some of its tests energise the heater and valves, so it isn’t something we’ll post here. For your purposes you don’t need it: Drain/Spin runs the drain pump on its own, and a wash phase with water in the drum runs the circulation pump, so you can listen to each one in turn with the machine on a tray.

If you do need parts, your full model number and the product number on the rating plate will identify the correct ones: https://www.whitegoodshelp.co.uk/shop/brand/miele/

Let us know what you find in the sump hose. If you can get a short clip of the noise uploaded somewhere and link it, that would help too.