The voucher cannot be passed on to anyone else and is also specific to the named installer.
Tony
FYI I do not believe the voucher is specific to an installer. The first guy who quoted me told me to apply and said I could use his Gassafe ID for the application but did not have to use him, and the installer is not mentioned on the voucher I have.
Quotes I received were both within a few £ of £3k. £400 is of course useful but there's still £2600 to find (included running a new 22mm gas supply about 20m).