What man/woman jobs have you been doing lately

[gbb]

If you haven’t got any improvement try disconnecting the hot water outlet connection on the top of the hot water cylinder, I used to find lots partially blocked with a hard substance, and we don’t have hard water issues to cause this issue around here. Turn off the cold feed valve to the cylinder first if it’s not jammed and run a hot tap until it stops 👍

This had been considered and you're right, it can be a primary cause. BUT, in discussion with my son (qualified gas engineer) his first reaction was...'at over 50 years old, good luck getting that off without damaging something'
So i've kinda left it, knowing it could well be responsible. The thought of losing the whole system in winter ...nah.