Received the following email from Andrew at Angus Aviation regarding the issues with the Gretz heated pitot:
Thanks for the email. Well done in finding the problem.
Since we have started producing the pitot at Angus Aviation we have discovered that this can occur during the moulding process. Our pitots are now fully tested to be sure that both the heating and thermistor circuits operate correctly and remain fully independent.
I will send you a new pitot today. Sorry for the inconvenience.