The warranty for your HIU and heat meter lasts for 24 months from the date that it’s installed and commissioned. This means that if your HIU and heat meter are installed and commissioned on the 16th May, but you don’t move in until the 24th August, the warranty will runs for 24 months from the 16th May, not the 24th August.
You'll find a sticker on the front of your HIU which shows the date it was commissioned and the date that the warranty expires.