An interesting question. What symptoms are you seeing?

I am having the same problem, my site is 10 years old, was top 5 and now nowhere in the first 5 pages.
Google has also taken away the title and replaced this with the domain url for this key-phrase search and similar ones.

Any ideas?

Now Google in their infinite wisdom things i mean fans as in desktop blowing fan.

To disambiguate either synonyms or homonyms, Google looks at the context of a word. Chances are by now that Google is looking not only at the context of words on your pages... it's also looking at the context of the word on inbound linking pages.

If the vocabulary on your pages is sparse (which it might be if your enthusiast site were, say, a photo gallery), or too heavily focused just on the main keywords, Google might still get it wrong. Disambiguation is a difficult problem. I have certain pet searches I use to test the disambiguation capabilities of a search engine, and I will say that Google gets it right more than any other search engine I've seen.

So I'd look at whether there is enough co-occurring vocabulary on the site (as opposed to the keyword itself) on the page for the context you're intending.

To use the example you provide, one kind of fan suggests an electric appliance, air flow, cooling, blades, material of construction, size, wattage, possible features, etc.

The other kind of fan suggests (as you say) supporters and enthusiasts, following, manifestation of interest, meetups, events, memorabilia, etc. It suggests also that you'd have a set of pages on your site focused on aspects of the particular fandom you're pushing, whether celebrity fandom or the following of a particular hobby, activity, sport, whatever.

Great illustration of co-occurence, Robert.

Thank you Robert, excellent advise.

The site is in fact a forum and the page in question is the homepage, so content is currently very thin other than links.

The links anchor text pointing at this page are currently only for the brand name and thus the product keywords, again probably not helping.

I will look into adding more content and more inbound links with suitable anchor text related to the proper topic and see if that sorts it out.

Thanks again.

Trying to control inbound anchor text at this particular point in history might be a big mistake. I'd initially focus more on adding text content to the page. Please let us know how it works out.