i have a firebird combi 90 oil fired boiler.....when i turn on the tap for hot water all im getting is luke warm water also when i select the heating to go on nothing happens....but if i leave the heating on i may find that it pumps hot water speradically for about 10 mins then thats it!!...the pumps are fine cos ive checked them...the flow valve was replaced about 6 months ago...the boiler will not fire up when im drawing off hot water (luke warm water) but it will fire up speradically to bring the boiler up to temp....all a bit complicated but can anyone help???