New immersion tank-grant?

When you say "immersion tank" you mean the hot water tank that has an immersion element? (when i read it i thought of some tank you were putting in a hole in your garden...)

Anyway,
Look at seai.ie - what you're saying sounds like the warmer homes scheme. Not sure of entire details, but they do things like provide insulation e.g. lagging jackets, attic insulation etc - I think they do it for free but you have to be in receipt of government fuel allowance or job seekers - there may be more.

There's a more broad scheme where anyone can get a grant towards improving energy efficiency, but not for what you describe. This would cover replacing your gas boiler with more efficient one, or installing solar panels etc.