[dooleyboy]

I planted a lawn 2 years ago, at first it looked perfect but at this time last year it started to die off in large patches, I replanted it at the start of this summer, again it took perfectly and looked great all summer but now it started to die away again, I put lawn feed on it, cut it regularly, drainage is ok, I’ve forked it a few time and it gets watered but nothing seems to help. Any suggestions on how I can stop this from happening?

[James Kilkelly, was GPI.]

dooleyboy subsoil is the most probable explanation.
Sowing lawn seed on poorly prepared soil which includes a mixture of subsoil is a common problem which throws up all the symptoms you mentioned.
Subsoil (usually light in colour) on the surface of ground or mixed with topsoil has ruined many the new lawns by causing hungry looking brown or yellow patches.
Subsoil is low in organic matter and topsoil is high.
Organic matter in the soil determines how much water and nutrients stay around the roots for your lawn to access.
If you sow seed into a mixture of subsoil and topsoil (usually darker in colour), it follows that your eventual lawn will be patchy and many shades of brown, yellow and green after its initial honeymoon period.
Subsoil could never hope to sustain grass growth over the long period, and that is why the lawn perks up with an application of fertiliser, but then slumps back to a weak colour once the boost wears off.

One remedial measure you can carry out in such a situation is called top-dressing
It's a way to gradually build up the organic matter in your lawn soil without starting from scratch.
With topdressing in your case a really thin layer of finely graded compost mix is spread over the lawn surface.
I'm guessing that the mix in your case should be approx 2 parts quality topsoil and 1 part peat or homemade compost.
A quarter-inch depth of this dry mix is all that is required any time it is applied.
Spread this all over the lawn and brush in to prevent swamping the grass.
This is best done in autumn and can be carried out each year to slowing build up the quality of turf.

If you post up a few overviews and reasonably close up pics of the grassed area then we may be able to pinpoint your problem and help you more.
How to post pics on the forum.