The boiler was installed after the cabinets. They might be removable but it doesn't look easy to me.
The boiler was supplied and installed and the first two services carried out by a company called "Flameout".
What no-one has yet explained is how Flameout fitted the cover after installing the boiler (which I imagine has to be done with the cover off). If they could fit it then someone else should be able to remove it again.