HW tank heated by heat pump monitoring - initial results

I’m waiting for my plumber to install the flow meter before I can finish installing the heat pump monitoring, but in the meantime I’ve connected the thermal sensors to my hot water tank to see what is happening.

Our heat pump has a valve on the (glycol) flow to divert either through a coil at the bottom of the HW tank, or to the heat exchanger for the central heating.

I’ve got sensors on the top thermostat (green shaded), and both the flow (red) and return (blue) - top and bottom - of the heat pump loop. I’ve timed the hot water on the Valliant system to come on twice a day: 13:00 to 14:30 and 02:30 to 06:00.

What I find fascinating is the delta on the heat pump loop at different times, and the fact the flow remains very hot despite the valve redirecting to the central heating loop outside of these times.

Right now the Valiant app is telling me the hot water temperature is only 25 degrees. That thermostat is near the bottom of the tank, but I’d have expected 3.5 hours of heating to have heated the whole tank of HW, considering it started at about 35 degrees. Perhaps I need it on for longer.

Has anyone seen this before or can explain what is happening? Many thanks in advance.

On my Ecodan system, the 3-way valve switches back to heating at the end of the cycle and circulates the hot water through the radiators to cool it down, but you do seem to have something odd happening here. I might have suggested that you have the flow temp sensor on the wrong pipe - i.e. it’s on the leg from the 3 way valve going to the tank, rather than on the common flow. However, that doesn;t really explain the sudden drop in temperature! Mine looks like this:

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