You can tell if there is an airlock (a bubble of trapped air) in your plumbing system if the taps (usually the hot taps) have reduced water flow, hiss and spurt water or stop running altogether. Airlocks are common, particularly if your system has not been used for a prolonged period, but can be fixed quite easily.
You will need a length of hosepipe, fitted at each end with tap adaptors (bought cheaply from any garden or DIY store), some old cloth and possibly a screwdriver. Connect one end of the hosepipe to the hissing or stopped tap and the other end to any mains-fed cold tap, such as the kitchen tap. If the tap causing trouble is on the bath and the hosepipe will not fit properly, connect it to the hot tap of the bathroom basin instead.
Open the problem tap all the way and then turn on the mains-fed tap. The pressure of the water from the mains-fed tap should be enough to blow the air bubble out of the system and cure the airlock.
If an airlock keeps reoccuring it means that air is being drawn into the system for some reason. You will need to find and fix the problem or that length of hosepipe is going to get a lot of use.
– Is your cistern large enough to handle your household water requirements? If not, each time it fully empties, air can leak in and cause an airlock. The standard size for a cistern is 230 litres.
– Is the ball valve on your cistern sticking or slow moving? Watch the cistern empty as you run a bath. If the ball valve is not opening quickly enough, the cistern will empty and air will be drawn into the system. If so, remove and clean the ball valve, or replace it if needed.
– Is the pipe from the cold water cistern to the hot water cylinder too small or blocked? If the pipe is narrower than the standard 22mm, hot water being used to fill a bath, etc, may not be being replaced quickly enough and air could be seeping in.