A banging noise from my heating system

I have had a problem with my home heating for a few years and was wondering if anyone on here could suggest how I might cure it?

Every now and again, when my heating has been on for quite a while and I assume that I build up too much hot water, a banging noise starts from the pipes around the hot water tank in my hotpress. It stops as soon as you make the slightest of turns on the thermostat knob on the pipe leading from the tank. But it could then start up again in another half hour or so.

The only way I could get this to stop was to turn the thermostat knob up very high, to around 70deg. But this left my water very hot and almost dangerous to put your hand under the tap.

Is there air in my system or what?

Don't know much about heating systems, but my parents use a stanley oil cooker for cooking, heating and hot water. If too much hot water builds up in the system it does the same thing and we turn on the pump for the central heating releasing the hot water from the cylinder into the system, alternatively the water is used for a long hot soak in the bath!! It has always been this way and is not a problem (my uncles fit boilers and are expert in this area) it's just the way the system is set up as my parents wanted full control over the heating system and did not want automatic pump cut in.

It was happening to me too and then I would hear spurting in the attic! But I got the thermostat on the cylinder replaced and so far so good!

Hot water cirulates from your back boiler/stove to cylinder, the cylinder will absorb as much heat as it can. When you hear the banging, it is hot enough. Your thermostat should kick in before this. the thermostat activates the pump that sends the very hot water around the radiator system.

You may have a faulty thermostat, but I belive if it is an old problem, the thermostat may be wired wrong. try rewiring it first, there is just two cables. Your stat seems to be working in reverse order I.E has to be very high to activate.

Thanks all for the replies.