did the installer design your system? if so you have paid for the design ,supply and installation of a heating system and those receipts are a matter for the plumber and his suppliers.his suppliers, not yours.
what matters for you is the registration of the boiler with gassafe or oftec as an oil tank is involved and also that your boiler benchmark book is filled in. these are the things that matter in regard to warrenties.
the most important thing of the lot is, was the system flushed and cleaned? before another drain down and then refilled with inhibitor, because these will concern your boiler reliability and i can assure you that if you have a warranty problem that involves a visit from an engineer sent or employed by the manufacturer he/she will will be able to confirm system cleanliness, by chemical testing, and may use that test result to charge you for repairs that you thought were covered by them