Be Careful
I would be careful if you are thinking about using New Boiler Grant, there web site, newboilergrant.co.uk has all the signs of a scamming site, e.g.:
1. The address is a Virtual London address - that is a holding company that lets people use their address to register their business and forward any mail etc. to the real address that is confidential.
2. There is no contact telephone number and this is where we have had experience with this suspicious web site - On their contact page is a form and in the telephone field is an example telephone number, that number is my personal number and has nothing to do with New Boiler Grant, but because it is the only number on the site, people call this number, they call me! - I have reached out to the company to remove this number but these requests have been ignored. A telephone number can be found on their Facebook page but when called it continuously says you have dialed an incorrect number, please check the number and try again, not even going to an answer phone. If you dig into their Terms and Conditions you will find a telephone number, the same as appears on Facebook page.
3. At the bottom of most reputable web sites it is common to find all the companies registered details of an operating company as found on Companies House Register , e.g. their Company Number. Whilst there is no law stating that companies must state this on their web site, that lack of transparency should be a alarm that the web site might have something to hide - As a side note, if a company in registered in Scotland, and you are in England, beware that the same legal consumer rules do not apply and if there is an issue, starting proceedings against companies in another country is difficult and your UK legal resources may not be able to help you. Buyer Beware.
I recommend you find a boiler grant via one of the more trusted site such as .gov sites or Which or Corgi or CIPHE etc.