That does sound like a potential restriction or scaling issue, especially with the fluctuating flow and noise under full load. Given the boiler’s age and repair history, it might be worth checking the plate heat exchanger or pump first—but you’re right, a full replacement could be the more...
For a reliable and cost-effective wireless alarm, both Ring and Yale are solid options. Ring is great for smart-home features, while Yale is simpler and subscription-free. Depends if you prefer more tech or straightforward reliability.