baxi bahama 100 losing pressure

[jonjackson]

i have a baxi bahama 100 combi boiler, recently it has started playing up, it keeps shutting itself down, whenever this happens i top the system back up with water, i have checked all the radiator pipes to see if any of them are leaking, they arent ! i have bled the radiators and the one closest to the boiler had a fair amount of air in it, i bled this off refilled the combi unit to reach the necessary bar for operating but over the course of time this pressure drops and the boiler cuts out, i then repeat the procedure of increasing the operating pressure, sometimes it will go for days , at other times we have to reset the boiler a few times a day, can anyone please advise me of the possible fault as baxi are offering £90 for a service or £170 for a guaranteed repair whatever the fault, if it is likely to be a major fault it will pay me to get them out on the £170 tariff, if its something simple i need to look at other options, i have given as much detail as possible, any advice out there would be gratefully received

 

[kevplumb]

is the pipe outside damp
does the pressure rise above 3 bar when running
is the boiler noisy (stupid question its a bahama) any more than the norm

 

[jonjackson]

the pressure relief pipe is totally dry, the baxi makes no more noise than normal , and no the pressure guage does not rise when running, as i have said the strange thing is it can run for days without having to reset the switch all of a sudden it will lose pressure and we may have to reset a couple of times in one day !!