Screaming central heating pump

[martinmich]

Screaming central heating pump?
every now and then my central heating pump makes a loud screaming noise (running dry ) i have an open vented system yplan i have checked the header tank and it is full if i drain water from the system it refills as expected i cant work out why the pump keeps running dry i have to bleed it becoming more frequent i have also removed and flushed the pipe from the header tank to the pump so im sure there is no problems there please help

 

[Agile]

How much higher is the F&E than the pump?

Tony

 

[martinmich]

How much higher is the F&E than the pump?

Tony

about 4 foot

 

[martinmich]

How much higher is the F&E than the pump?

Tony

about 4 foot

just seems strange the system is about 4 years old and has only recently started doing it