Start with the information you already have: your boiler make and model, the number of bathrooms, any recent faults and whether you want the boiler to stay in its current position.
Think about the changes ahead
Tell the team about planned extensions or changes in hot water demand. Include a preferred installation period if you have one.
Keep it straightforward
You do not need to diagnose the system yourself. Share what you know and choose Not sure where needed. Photographs may help later, but do not open equipment or access unsafe locations.