Yesterday I mentioned a possible "net loss" due to switching on pump: a temperature drop in the storage. I was guilty of jumping to a questionable conclusion.

This what I observed this morning:

If you compare it to the image in yesterday's log, the effect is even more pronounced. The main difference is that more hot water had been consumed yesterday evening. I now offer a different explanation: the sensor is above the heating coil in the storage, and (more heavy) cold water is below the point ofmeasurement. By activating the pump, the coil exposes the (warmer) water above to a lower temperature. The net effect is that cold water at the base of the storage gets heated.