Bosch dishwasher inadequate heating (SRS46A02GB/08)

[julianbradfield]

I know heating problems are a VFAQ, but I haven’t seen this precise description in my searches, so advice would be appreciated!
A few years ago, the machine stopped cleaning effectively on the eco cycle, so we switched to the auto cycle. This was ok for a while, but now it (a) sometimes seems to fail to heat the wash effectively enough to wash (and I’m not sure it ever heats it to the intended temperature, as eggy cutlery is often left not quite clean); (b) never dries very effectively, even with intensive drying set.
However, it always passes a self-test cycle, and the interior is piping hot and everything dry when I open the door at the end of the self-test cycle. Moreover, if it has failed to heat properly during a normal wash cycle (as evidenced by dirty dishes), running the self-test fixes it until the next time it fails, maybe a few weeks later.

Are there any most likely causes? (The dry joint problem, maybe? Is this one of the models affected.)

[Martin]

Re: Bosch dishwasher inadequate heating (SRS46A02GB/08)

Intermittent heating would indeed indicate a dry joint on the control unit board, the heater relay pins often the trouble. So it’s worth checking the PCB.

If that isn’t the problem then the water flow diverter unit ( the device that switches the flow alternately between upper and lower spray arms) could be jammed. If that were so then only one spray arm would be working, the other devoid of any water. Symptoms there would be that only one basket cleaned perfectly the other not so.

[julianbradfield]

Re: Bosch dishwasher inadequate heating (SRS46A02GB/08)

Thanks for those hints.

However, after spending more time watching it and taking its temperature etc., it turned out not to be a heating problem at all, but a filling problem. It would fill for the pre-rinse, usually fill for the main wash, but then not fill for the rinse.

I’ve just taken the left side off and cleaned out the gunk from the float chamber etc. I also noticed, twiddling the overflow detector, that the overflow float seems to be a tiny bit too sensitive – if I nudged it up to to operate the microswitch, it didn’t invariably fall back enough to release it. So I wonder if a mix of vibration and thermal expansion has maybe been randomly flipping the overflow switch. I tied a small nut on to it to change the balance a little (but small enough that water should still operate it!).

Previously, when I’ve run the self-test, it has always started with showing 2 or 1, and then gone to 0 and stayed there. After putting it back together, the self-test ran showing 0 at all times.

We shall see whether a wash works properly tonight.

[Author]

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