Why is moving my 8 year old Vaillant Ecotec boiler 6 inches lower a bad idea

It would involve either coring a new flue hole or extending the flue itself, an entire days work to move it and shorten all the pipes etc and you would need to check that you still had at least 200mm after the move to ensure enough clearance to repair the boiler should it go wrong, as this will be the min clearance set out by the manufacturer to honour the warranty. It would also need to be recommissioned when the job is done. Cost circa £500-£750 depending on the flue changes.

I would always advice customer to replace with new boiler rather than moving a nearly 10 year one. Will be more cost effective in the long run when you consider energy savings and manufactures warranty against cost of moving existing and paying installer.

Its going to cost the same amount to fit an old boiler as a new one so why refit old and then in a few years pay to fit new one.

i recommend, to get new flu kit, for this type of boiler,, clearance from gutter and openable window cover M-I, pipe work you will need including gas,, and the cost, will be 800 pound, and have to be done by a gas register, buto you can do what you like mate, within gas safety regulation, i am agree with previous answer, well done mate.