The end is not actually missing, the bit that stops birds entering (looks like a bulls eye fixed in three places) is damaged - one fixing has 'melted' away and a second is on its way.
This has happened before and the whole flue had to be replaced at the request of BG service engineer.
So...
Hi,
I have a Vaillant Boiler (not sure which model) and I need the part number for the bit at the end of the flue that prevents birds from entering the flue.
The Villant part number for the whole horizontal flue assembly is 303933 but I only need the end bit!
Many thanks
Jeff
Had a similar problem after removing a rad to decorate.
After draining the system for the removal and refilling it would loose pressure.
When it's pressurised and you run the boiler does the pressure go up. Mine did and when it reaches 3 bar it vents additional pressure out the vent...