need help making old back boiler redundant (please)

[Ryan Smith]

as above looking to make my old back boiler redundant ,


reason is that i have had a new central heating system installed , that has made the old coal fire back burner no longer usable ,


since this has been done the contractors did not drill the old back boiler ,
instead they left the pipes open up at the hot tank


now the fun bit , i have installed a insert stove into the old fire , problem i now have is that when i have the stove lit the stove is bleeding some heat into the backboiler , causing the boiler to blow steam of up at the hot tank where the back boiler,s pipes have been disconected ,


so im looking to remove as much as possible water from the back boiler , and also make sure the boiler will never be used again ,


where do i drill ? or can i drain from the pipes at the side of the fire ?
i have uploaded pics to help ( if more pics needed let me know )


thanks ryan