I checked the connections to the board, they were slightly loose so I retightened. No scorching as far as I can tell.
Heating the head up worked as previously, but as soon as it reached the manually set temperature it would start to drop again. Restarting the machine didn't help, the head refused to heat up now.
I updated the firmware, reassembled the head and everything else, and it heated up fine and stayed at the assigned temperature, and I could increase / decrease the temp. I did a small test print which started out fine (it didn't stick to the bed though, so I aborted)
On the second print the print starts coming out blobby again and after a minute the printer stops with:
Error - StoppedHeater Error
On the support page Ultimaker.com/support I've checked the suggested check 1&2 for the error, so will see if the head is touching the fan assembly (#3). Suggestion 4 doesn't apply, so unless it's touching the fan assembly I'll have to open a ticket...
As a side note: The grup screw is what keeps the sensor and heater in the block, right? At least I can't remove them until I loosen the grub, so figure it ought to be tight.