Raypak
A Raypak model number is its size, and the suffix is the heat exchanger. What each letter means, what the warranty requires, and the manuals.
Heaters
Before you buy Raypak
Where you bought it decides the warranty
Raypak's pool heater warranty has a clause worth reading before buying online. In the United States it applies only to heaters bought from an authorized Raypak dealer, and Raypak reserves the right to reject claims on heaters bought from unauthorized internet sites or marketplace storefronts. It is not an outright ban on buying online, as Jandy's is, but a marketplace listing is exactly the case it names.
The residential Digital heaters get two years of parts and labor at a single-family home, and one year anywhere else. The bronze-header ASME versions get one year. Every one of them needs a properly licensed service provider to install it for the warranty to apply.
Read the suffix, not the size
The number in a Raypak Digital model is its size, not its rating: the 406A is a 399,000 BTU heater. The letters after it matter more. -EN-C is a copper heat exchanger and -EN-X is cupronickel, and Raypak says the copper and cupronickel parts are not interchangeable. A P prefix is the residential polymer-header heater; a B prefix is the bronze-header ASME model.