With this ring....

Today hopefully!!!! heralds the end of the ongoing saga of Mr A's troublesome boiler.
3 (yes....three) months this has been going on for...googling various bits & bobs, ebaying the parts, then back to the drawing board when it didn't work.
My input was 'just get someone in ffs' but this failed when they wanted to charge an extortionate fee (£524 total for parts & labour) for what has ultimately taken Mr A 10 minutes and £18.50 to sort.
The final repair, was the replacement of this little o-ring (£1 for a bag of 100!).

Next mission: Mastermind.
Specialist subject: Halstead Boiler repairs