Hello i would be grateful of any assistance. We have a potterton Performa 28i combi boiler installed about 6 years ago. We noticed recently that it has been rather noisy when running hot water or when it periodically self runs to maintain the vessel water temp. It sounds like a "girgling" noise. I've since noticed that when running hot water the pressure guage drops from just over 1 to about 0.5. Plus the heating isn't working at all. No fault lights are displayed. I've read all the forum's and can't find anyone with a similar problem. Any advice would be much appreciated. thanks.