You need to be more specific.
Boiler make and model.
Any Error codes?
Are you sure the fault is due to losing pressure? Could be due to over pressure which in turn will give an error code, shut down boiler and reduce pressure below required minimum to operate. Hence why you think it is losing pressure.
Have you checked for any leaks near rads, pipework, under boiler?
Can you re-pressurise the boiler using the filling loop and get it to work again?
Robert
October 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.