boiler trouble

[stgiles]

hi everyone,
can anyone tell me at what intervals should a boiler fire up to keep the water inside the cylinder heated. I have a potterton which is about 8 years old now and sometimes it will just stay idle for quite a while and then other times it will fire up every 3 or 4 minutes for about 30 secs, regardless of if there is any call for hot water or not. i have a hunch that there might be a problem with the cylinder stat or am i barking up the wrong tree

 

[Puddle]

You will propably find it starts and stops just as the water is reaching temp in cylinder,once hot all ok .this can be reduced by adjusting gas presures down slightly and getting flow and return temps right,needless to say this should be carried out by a registered gas person,this will also increase the life span of your boiler and reduce breakdowns caused by overheating