Signing off a boiler install and carrying out a gas safety check are two completely different things. When you sign off a boiler you are stating that it is securely fitted, the flue is correctly fitted etc. The only way you can confirm this is if you have fitted the boiler yourself. With a safety check you can only comment that things are working correctly at the time of your visit, you are not commenting on things that it is not possible to check after the boiler has been fitted and the making good done.
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