Air Lock in Domestic water system

Hoping this might help someone

Experienced dreadful banging in the water system due to air in the system. Very difficult to pin point the cause and took a couple of weeks to narrow it down.. At one point thought it was a loose jumper (which was very worn) in the master stop cock.

Setup Combi boiler therefore no header tanks or hot water cylinder. Old two store property.

Two identical close coupled Ideal Standard toilets installed about four years ago, one upstairs and one downstairs. About two years ago noticed water trickling into the bowl in the upstairs toilet from the cistern which was cured by replacing the Cistern Outlet washer. This is a 2.25 inch rubber washer which lifts as the toilet is flushed.

On the the occasion when the air locks occurred discovered water trickling into the bowl from the cistern on the downstairs toilet and found that the washer was badly eaten away around the edges allowing water past it and into the bowl, meaning that water was being continually replaced in the cistern.

Replacing the washer stopped the banging in the pipes immediately and has not been a problem since. (a couple of months has now elapsed).

Ideal Standard have obviously got a problem with the constituency of these rubber washers. This area has particularly soft water. Cheap enough to replace as a part, but to have them replaced by a plumber a lot of money.