In HOMER it allows you to generate hydogen but you cant connect it your boiler to suffice a heat load why is this?

In HOMER's simulation logic we used the simplifying assumption that the boiler is an perfect backup source of thermal energy, on which the system can depend to serve the thermal load any time the rest of the system cannot.

Fuelling the boiler with stored hydrogen would violate that assumption because it would be available only when the hydrogen tank contained sufficient fuel.