Boiler banging noises

[blueagle78]

I've a really strange problem with my boiler and I hope someone can advise what can I do to rectify this. I've got a system boiler Vaillant ecoTec Plus 630. I've got hot water set on the timer to come on 3 times a day. In the morning when boiler kicks in at 6am after about few minutes, banging sound starts and carries on for about 10 - 20 seconds. Then it goes all quiet and works as expected. I'm guessing air is entering in the system from somewhere which is causing this?
To make things even more strange if I set the hot water temperature upto 50 degrees on the boiler then I don't hear anything but then it means water isn't as hot as expected.
Any help / advise would be greatly appreciated. Thanks.

 

[AngelesPlumbing]

Dirt on heating or scale in heat exchanger

 

[jeff the gasman]

Possibly a sticking pump. The banging being caused by this and shock wave causing pump to start again.
Jeff

 

[blueagle78]

Morning guys, thanks for your input.
I was thinking it could be air in the system so I'm glad you experts know what's going on.
My boiler is still under warranty so shall I call Vaillant to fix this problem or my plumber?

 

[srhawksy]

Ring your plumber, he should check it then if Vaillant are needed it would be nice of him to ring them for you, I would but I'm just that nice

I't def the boiler?? Not pipes expanding with heat?

 

[blueagle78]

Ring your plumber, he should check it then if Vaillant are needed it would be nice of him to ring them for you, I would but I'm just that nice

I't def the boiler?? Not pipes expanding with heat?

No its definitely not the pipes expanding with the heat.
Another weird thing which I've noticed. If I reduce the central heating temperature to around 50 Celsius then there's no noise at all when boiler kicks in to warm up the water. However water is not as hot as it is when boiler central heating temp is set at 65!
Waiting for plumber!