Your boiler should have a bleed out valve to allow the system to be flushed, the lowest radiator in the house should have also been fitted with a skirting board level bleed valve. For the other pipes running under the floor (nearly all yours seen as its a bungalow) I have no idea how you empty these maybe its got a removable end cap on one of the pipes maybe where it goes underground after it exists the boiler.
Thats total speculation though, but FREE BUMP
