Low Boiler Pressure

hi i wondered if anybody can give me any clue as to why  my boilers pressure falls flat when i turn the heating of. iv had a new pressure releif valve fitted ,the pressure vessals ok. iv just had a sevice on it and everythings ok with the boiler yet everyday i have to repressurize the boiler  its really getting to me everyone says we must have a leak but we cant find one short of taking all the laminated flooring up but surely we have some sign of a leak thanks in advance if anyone has any advice sue

what sort of boiler is it?

combi or system?

Sounds like you definitely have a leak somewhere is it wooden floors or screed?

The pressure will drop when its cold but not to nothing. What pressure are you putting in it at cold and what is it at hot ?

It sounds like the pressure vessel needs pumping up , this is a large round metal container  (sometimes red) in the back of the boiler ,  That's done by a Schrader valve thats the same as you find on a car tyre & its done with a car tyre pump. Check the Manuel for the correct pressure

If its not that you have a leak, hard luck with the floors but try a bit of toilet paper round each rad pipe under the valves, this shows up  very small leaks

Yes I agree with the above I had a presure vessel lose presure and spent weeks looking for leaks and constantly topping the pressure up until somebody told me about checking the pressure vessel

if its the expansion tank, then the boiler will be blowing off regularly. is there any water at the blow off pipe at any time? if not, then its probably a leak

It could be the diaphragm in the vessel that is leaking and not holding pressure, had this on a valiant boiler, new vessel and problem solved.