Can I vent my combi boiler directly up through the roof space (with a flue obviously) and out through a tile vent etc. The outlet is on the top of the unit.It is currently situated on the outermost wall so Its vented through the wall, we are having an extension so don't want to move it.
As long as the correct flue is used this shouldnt be a problem, you will need to refer to the original installation instructions for more details on the different flueing options, as long as the boiler is not too old you should have no problem in getting the correct flue adaptors, however you should not attempt installing the flue unless you are CORGI registered.
not sure what you mean by a tile vent, normally for a combi boiler thats flued thru the roof you buy a special end for the flue which prevents water ingress, this normally extends thru the roof by around 12 inches.
If it is an older 28i then you can only flue vertically for a very short distance 600mm before turning it through 90 degrees to a standard horizontal flue terminal. If it is a newer greenstar 28i then you can easily flue vertically using the correct vertical flue adaptor, a vertical flue terminal and pitched roof flashing kit.