No hot water yesterday morning, and on checking no heating either. I assumed it had lost pressure, but for some reason didn’t just fill it from the remote loop like I normally do, but went up into the loft to have a look. F75 code on the screen, which Google showed could be a multitude of things. Water dripping out of the casing. Booked a British Gas appointment for 08:00 - 13:00 yesterday (this was about 10:30) assuming no one would show up. Hour later a cheerful gas man arrives. Quick check and the heat exchanger is leaking. Part ordered, bucket installed under drip and repressurised, and he’s off. 08:30 this morning he’s back with the exchanger and new pipes as apparently they can be a bugger to remove from the exchanger. Couple of hours later it’s refilled and tested with a clean bill of health. From fault to fixed in 24 hours. Can’t argue with that. Great service from British Gas.