combi double feed tank/cylinder rads hot but water cold!!!

[mannersme]

was wondering if anyone could offer any advice, the system was recently drained for a radiator to be changed.
After refilling all rads were bled, as well as a bleed valve situated near the cyclinder.
The radiators are working fine if anything they appear to be a little hotter than normal but the water is running tepid at best,.
When the hot water/central heating is running there are several things happening (not at same time and not at set intervals, just randomly. if that makes sense)
Some banging from the bolier, each `bang` makes the pilot light burn bright orange momentarily.
Sounds like an aircraft taking off from the boiler, after a click sound noise dies down.
pump seems to be trying `to hard` whirring.
can here water whoosing through pump.

I`ve added a picture of cylinder just to be sure, but if it is a combi cylinder then surely draining the rads would have no effect on hot water supply, or is this merely a coincedence??

Also water does heat up if the immersion heater is used, although this takes several hours.

many many thanks in advance for any help, Seems i`m nearing the `christmas approaching everything conk out` period of our household again.....never rains eh!! lol [/img][/img][/img]

[mannersme]

today when heating and hotwater are turned on, pump seems to get louder and louder, when noise peaks water bubbles and glugs (in a grey chamber that has 2 pipes goin into it and 1 that appears to fill the tank from the top) then air escaping from the pipe that hangs ovet the top of the tank, followed by a little water (a few cups at most) then pump quitens down and cycle starts again.
Is this the air that I think must be trapped escaping or is the system pulling air in??
thanks in adavnce for any help