suprima 40 rumbling

[gg1a]

i have a suprima 40 combi ...i know nout about central heating ....but my boiler makes a rumblin sound \banging ...like its goin t explode ...then a click \sound ..then goes quiet...this happens every half hour or so.....the waters hot but not enuff to fill a bath ?........the pilot light cums on then goes off ...but ..seems as tho it wants to come on at times but no flame ...clickin noises ..the white plastic cap at top of boiler also pops off now and then ...vented rads ...water coming out and pump..when turning silver screw ..need help fast ..
ty

 

[kevplumb]

your right
a suprima aint a combi
would think the heat exchanger is fouled

 

[gg1a]

how do i correct ?...is this expensive to replace?....its a potterton suprima 40 ...in conjuction with a boilermate 2

 

[kevplumb]

thermal store think wait for oilman seems to be up on these things
(or he knows a man that is )

 

[gg1a]

ty