Hi everyone just wondering if any one could help me out, just been to look at a boiler for a customer complaining of loss of pressure to his boiler when running heating an hot water at the same time on s plan system. If he just runs heating it's fine but soon as you open mv for water pressure starts to drop an eventually boiler goes to lock out boiler is helstad Eden 30sbx. It's a big house with a lot of radiators my thought was that there is to much water within the system when mv is open an its creating a negative pressure on expansion vessel an a bigger one would be required. Any help would be great thanks
