Unlight

Hi all, wondering if anyone can shed any light on the below, as I can’t get the car booked in for a few weeks. 2019 Kodiaq VRS. About a month ago, got the eml on, Carista OBD device stated it was a glow plug module. No probs, replaced it but error message came back. About 2 weeks ago, got into the car after it sitting for a week unused, EPC and limp mode comes on, along with a “glow plug 1 open” and P02CB under boost code. The glow plug 1 open message has disappeared, but I’m still getting the EPC light on regularly, which I can reset using the OBF device. Even with the new glow plug module, I’m still getting the error message for it too the odd time. Car due a service imminently if that’s a clue for anything. Any simple things I can try before booking the car in? Could really do without a huge bill.