boiler and megaflow in airing cupboard

moneyspending

The space we have is 1000 x 800 mm. 2.5 m height. Is it impossible to install boilder and 250l tank (1738 mm height)?

Can go for 210l tank (1486 mm height).

nofoollikeold

Pretty unlikely that you could mount the boiler above the Megaflo. The 250 litre Megaflo is about 1,800 mm high, which would only leave 500 mm for the boiler.
If you go to the web site for Heatrae Sadia and the web site for your proposed boiler, you will find (probably indirectly) diagrams of their dimensions, layout and clearance requirements. Mock these up to scale in bits of card. Make an allowance of 75 mm extra "sticking out" for all pipe connections in addition to an allowance for clearances. See how the mock ups map on another piece scaled from 1,000 x 800.

Try side by side, or with the Megaflo on the long wall and the boiler at right angles to it on one of the 800 mm walls, or vice versa.

Missed your 1,486 mm dimension, but same applies unless you can find a boiler which is less than 800 mm from top of flue (or boiler casing if flue out of the back) to bottom allowing for clearances.