@prezes Thanks. That was helpful.
We were away for 4 days and should have followed the emptying procedure. We didn’t. The water became stale. Used the stale water to fill the tank to pull a couple of shots.
I couldn’t drink the Americano as it was tasting very weird and bitter. The cup was from the same set of beans that I had used before going away. Normally, the empty cup (after drinking the Americano) would be usually clean except the usual light coffee stain. I dumped the coffee in the sink. The entire cup was lined with thick black stains. 😅
The anniversary filter change was also due, although the unit didn’t ask for it. Took almost 2 hours to sanitise/descale, go thru’ the filter change and flushing 10L of water.
I will be flushing out the brew boiler with fresh water now before my morning cup.