Could anyone help please. I have an old Potterton Puma 80e, which seems to lose pressure pretty quick, I noticed that the pressure was below the red line yesteday evening. so I topped it up to 2. 5 and turned the central heating on for 2 hours. Then I had to go out, so turned it off. By the time I came home again, about 4 hours later, the pressure was back down below the red line. Help please!!!