Siemens dishwasher SN65M030GB/16 - water doesn't heat

[YorkshireMidge]

Our dishwasher is playing up. It will run through the entire cycle, but isn't heating the water. This machine seems to be similar to other models from Bosch and the like.

I've tested the following:

1. Checked the heater pump motor is running (it is)
2. Checked whether the heater bit of it gets warm (it doesn't - no surprise there)
3. There are three thick red wires going to the heater element (I assume economy and full heat) and I'm seeing 10ohm between them suggesting the heater elements are both fine
4. With the machine running*, I've had my meter across the coil of the relay on the control board that switches the heater on and I never see 12V so the relay doesn't seem to be operating

*The control board is live so don't do this unless you know what you're doing.

I have found that if I use the lowest temp programme (45 degrees for delicate glasses and the like), the relay for the heater clicks in and water starts to warm, but just not very much - and the heater pump seems to sit there pumping water through, and never gets to the point where the spinners start turning.

On the hottest 70 degree programme, I have seen it throw an E09 error once.

 

[YorkshireMidge]

I've found my problem. The heater pump impeller has broken up - and it seems this is a common problem. The blades on the front half of the impeller have little pegs which go through the back plate of the impeller and are then melted like rivets. In my case, the pins have sheared off so the motor is running, but not circulating.

I assume on the hotter programmes, the water around the heater gets too hot too quickly and shuts down because there is no circulation. On the lowest temp setting, it seems to kick in for a while and then shut off.

I've taken the impeller off (note: left hand thread) and done a temp repair by gluing the two halves together, and then drilling and tapping M3x12mm CS stainless steel machine screws just behind each blade and through into the back plate of the impeller to give it extra strength. It's now running happily again - but I reckon the adhesive will eventually fail with heat of the hottest programmes.

It's possible to get replacement impellers by the look but they are silly money for what they are, and at 11 years old, I think I'll bite the bullet and replace the whole heater pump. Hopefully they will have improved the design in new pumps by now! - this is just rubbish.

 

[YorkshireMidge]

A final note on this fault in case it helps anyone else. My new pump arrived today so when I'd dug my old pump out, I opened it back up to take a proper look. Once the impeller is off, you can lever out the front plate (which retains the rotating magnet) by working your way around the join with a screwdriver.

The spindles of the magnet were noticeably worn as you can see, and the push fit front and back bearings had worn oval - so there was over 1mm play, and the magnet was obviously making contact with the casing. My temporary repair had held and would probably have been good for another week or two.

So, all things considered, I'm glad I went for a replace.