pipes making knocking noise

[mckenzie]

Please can anyone tell me why the pipes make a knocking noise when the heating/hotwater first comes on in the morning?

It doesn't last for long - maybe about 8-10 knocks. It's enough to wake me up though.

TIA

it might be air in your system. we have a small sort of tap thing thats on the pipe in the airingcupboard. you have to turn it so it adds water to the system and gets rid of air - until the pressure on the gas boiler reaches about 3 i think - it needs doing now as only 1 and making banging noises. don't overfill as i think the plumber said it can explode. are the radiators cold at the top because they've got no water - this is another sign

thanks very much dreamingofsun - I'll go take a look at the level. the little tap only goes one way I seem to remember so how do I know whether I am adding or taking water away?

the dial on your boiler will move up as the water pressure increases. it can happen quite quickly - so one person needs to watch the boiler whilst the other fiddles with the tap. if its like our tap - which only goes one way - it will only add water. hope its the same as ours - difficult to tell without seeing it. just be careful you don't put too much water in - i think this can cause big problems and i've no idea what to do if this happens

My pipes creak when the hot water comes through them first thing in the morning - it's just the metal expanding as the hot water goes into cold pipes.

Knocking noises can be air in the system though. I refer you to the previous poster's advice on that, as I don't know anything about it (other than how to bleed a radiator that's got cold spots).