Have had re-ocurring problem with this since we bought our house 3 years ago. Our boiler is in the attic and our immersion tank is in the downstairs cupboard. We have to bleed the pipework every 3-4 weeks to cure the air lock then it reappears. Once bled it works relatively well then gets worse and worse over 3-4 weeks untill it completey fails to even drip.
Does anyone have an idea as to why this might keep happening??