On Friday, May 15, 2020 at 12:36:57 PM UTC+1, polygonum_on_google wrote:
On Friday, 15 May 2020 12:02:33 UTC+1, JoeJoe wrote:
a 4 x 4 treated wood post that was in place for around 15 years has
rotted and needs replacing.

It is a 2.4m one - 60cm under ground, set using a couple of bags of
postcrete. Unfortunately the post has rotted right at the ground level.

Once I free the post from the rest of the fence I am certain that I will
be able to simply snap it at the point where it meets the concrete.

Is there an easy way to remove the lump of concrete so that a new post
can be easily set in its place without having to dig a very large hole
around it and pull it out?

Any suggestions will be appreciated.

PS: I do not have access to any heavy machinery.

If the post is well and truly rotten below ground, you could remove that rotten wood. Then you should have a fence-post shaped hole. OK, might not fit perfectly but a little bit of fettling might be enough. If needed use stones, sand, wedges to stabilise the post and make it vertical.

Fence posts generally rot at surface level as the process requires oxygen ISTR