biasi combi boiler 24s problems no hot water noisy

hello to all of you on here. i have a biasi 24s combi boiler which is the prisma model. Basically when i bought my new house a few years ago this boiler was installed in the bedroom next to the window. The boiler has the following problems:

There is no hot water. the water goes hot, then cold, then hot and then cold again. I cant even have a proper bath as it is relatively cold water.

The boiler is always making a noise as i turn on the hot water or central heating. The boiler pressure has always been going down slowly below 1 and i have been repressurising it every few days to be between 1 and 2.

In my bedroom, the windows are all condensated. The walls are wet next to the boiler. The double glazing is fine. I have checked all the radiators for leaks and there is no visible leak.

The central heating is always warm. The radiators warm up well, very hot.

I have had boiler guys out to look but most of them seem useless. They just want a quick fix, make their money and go away and the problem always seems to be there.

I really need this problem fixed. Any help will be highly appreciated.

Well it's not to good around your place than ?

H W problem I would suggest that it is probably a scaled up plate heat exchanger (maybe ?) when in the hw mode the temp gauge on the boiler should achieve approx 75 degs c , does it ??

there are other factors or reasons why your hw is not staying on , but I would go with the above for now !

Loss of pressure ?? as u are probably aware ? u have a leak somewhere ? wet walls ect check the pressure releif valve which should be terminated outside , is it dripping or showing signs of letting bye ? is it turned back to the wall ? hence the wet walls may be ??

boiler noisey ? probably ketteling ? maybe ? meaning that the main heat exc needs descaling / flushing / with chemicals ?

Would suggest you get some one to look at it for u , ask around , there are numerous good boiler engineers around that will be able to help u !

The Biasi Prisma/riva were a pretty good boiler , hope it go's well !

thanks for the reply. I understand what you are saying about the leak in the system somewhere.

Loss of pressure as you know my boiler is in the bedroom. The pipe going out of the boiler outside is a 15mm copper pipe, which is the outlet pipe. It is just a straight pipe going outside. Do you think i should get this pipe taken out to see if it is leaking? What about the flue, can that cause condensation to the windows?

A year ago the diverter valve was leaking, so i got that changed, but the slow loss of pressure still continued. Can there be something within the boiler that has a slow leak? Such as another part? Maybe this is why i am losing pressure? Any ideas? If the leak cannot be on the central heating pipes, i am assuming, maybe there is a leak internally in the boiler?

About my noisy boiler - i cannot afford 300 pound for a powerflush so i have gone out and bought sentinel X800. Is this good for cleaning the system? Will this also clean the heat exchangers if left in the system and then do a mains flush? Can anyone tell me the best way to do a manual mains flush to clear the system out as much as possible? Thanks.