Welcome to this friendly forum, Which Way!
Are you sure that you have the correct grid reference? I’ve checked it on the latest edition of the
Explorer map and it appears to be close to a small pond and a large square glass house 500 metres due west of the river Goyt.
I’ve checked the key of all the OS 1:25,000 series and can confirm that:
First series: has no symbol for chimneys.
Second series: chimneys indicated by small circle. The first map appeared in were issued in 1965 but it was not until 1990 that the whole country was covered.
Pathfinder series: has no symbol for chimneys.
Current
Explorer series: has no symbol for chimneys.
It is interesting to speculate why the OS decided to omit the depiction of chimneys but it may be because so many were demolished during the latter half of the twentieth century that there was little point in continuing to depict this feature.
I'm afraid that it is an unrealistic to expect a 1:25,000 map to be absolutely accurate. Omissions and simplifications have to be made in the interest of clarity. Unfortunately, the OS does not publish the conventions it employs on its maps, and most walkers are blissfully unaware of them even though some of them are quite important. Most of them are listed and discussed in my book (see below). I don't have access to the 1:10,000 and 1:2500 maps but I'm pretty confident that your chimney would be marked on them.
Hugh
For a preview of the 5th edition of my book
The Walker’s Handbook; Everything you Need to Know about Walking in the British Islesclick on
http://walkwithwestacott.com. Then click on ‘Reviews of The Walker’s Handbook' in the Navigation panel to the right of the illustration of the cover.