Can I use unused tankless for heating?

I have a V-1 Burnham boiler with forced hot water heating. The tankless part has never been connected to anything. Can I plub this into my FHW system - I'll test for leaks first.

What's the point of using the tankless coil for space heating rather than the boiler itself? The tankless coil's heat exchanger, is not of infinite heat-exchange capacity, but is probably enough to handle moderate space heating loads. It's output capacity will depend on the temp you run the boiler at, which may be a a higher (==lossier, lower efficiency) temp than if running the heating system directly.

Sorry, I was not clear...

My boiler IS used for FHW space heating. Would it increase heating efficiency if I plumb the unused tankless coil into the space heating system. Thanks for your patience.