I tried it today, and after 5mins running it said it was 12.8 and after 10mins circulating, it said 13.1. This surprises me.
I tried it again a day later, letting the pump run for 15 minutes cold circulating, hours after it had last done any heating (so no heat in compressor) and it levelled out at 12.8. This gives a good indication of summer temperature.
The last 5-7m or so in each direction is running from the house to the borehole through the ground near the surface, which is seasonally warmer (and conversely colder in winter), so maybe that affects it. I was expecting it to be colder. I shall take weekly readings so see how this develops. I am already taking daily readings on the electricity consumption. Ice energy have offered to supply a meter specifically for the HeatPump, and I have bought an Owl meter to make it easier to monitor the overall house.