Old and never used PHE as delivered in 2018: (used as a transition from gas similar to you, but had always planned to move to a heat pump from around 2016)
Just as it was being installed (replaced with the new kit including new pump which seems to match as described in the pdf I uploaded in the previous message) by Octopus:
It was a bit of a nightmare actually as Octopus had no idea how to plumb it up or wire it up.
They didn’t pipe properly the small other pump that takes water from bottom and sprays onto top of tank, so that didn’t work and resulted in the first night top Mixergy inmersion only run (only 1 day heat pump work to be fair) hitting 80C at top of the tank and the pressure relief valve leaking water into the tundish….which then needed replacing with Mixergy parts (Octopus fitted as they messed up).
What made it worse it that my early mixergy tank has a bottom failsafe no -smart immersion that Octopus promptly decided to make their own, disconnect from my real dumb timer (failsafe) and connect into the Daikin controls….didnt work properly and can on at random times.
I told them the Mixergy controller has a legionnaires cycle using top immersion that can’t be disabled, and so come back and give me my failsafe dumb immersion back. They did do this.
It’s all working fine now though to be fair.