you will not get the answer to the problem with your boiler on here or anywhere else as the problem you have can only be repaired by an rgi.if you run your boiler without the casing on it you are putting yourself and your family in serious risk of carbon monoxide poisining,also it is against the law to remove the boiler casing unless you are an rgi as only we can test and certify your appliance is safe to use.do yourself a favour and call an expert, it might save your life instead of a few quid.
DEANO RGI
January 2011