Looking at oil fired combi boilers, preferably external boxes.
House does not have a header tank uses afortic tank on a very old
rayburn at present.
I have so far found two possibilities:
One from Grant, (http://www.a-b-d.co.uk/Grant/Grantoutdooropt.htm ,
and the other from
Turco (http://www.thermsaver.co.uk/turco/boilers.html ).
The Grant uses a Riello burner which seems to ber rated Ok.
usenet at lklyne dt co dt uk