Not strictly true to say that there is nothing wrong with taking the cover off.I may have worded it wrong but there is nothing wrong taking the cover off. So I need a qualified GAS SAFE register to do it??
Basically, if the cover is anything other than a decorative casing/electrical enclosure, then you need to be 'competent' to remove it. So, while not all boilers have cases that require you to be 'competent' in order to remove them, people on this forum are justifiably reluctant to encourage others to remove the casing, as many boilers have a casing that is functional as well as decorative.
If I know the make and model of the boiler, I can check in the installation manual first to see if I can, say, access the bleed valve if need be, or get to where it is wired in before I start work on the system. Since we don't even know the model, we have to assume the casing has a functional aspect, so we cannot advise other than to say that if the casing needs removal, you need a Gas Safe registered person. Sorry.