Speedtester ... grrr ...

I've used the bt speedtester occasionally for yonks. Recently, however it has taken it into its head to tell me that 'Number of threads are 16!', but FAQs don't explain what this means to the hapless btinternet punter.
Also, perhaps someone can explain why my last two tests have displayed "Exception:: Connection refused: Connect" when my link to the net is fully operational and all info requested (phone no and user name) has been entered correctly.
Finally, today's test appeared to complete satisfactorily but didn't display the results. Instead it went back to showing "Number of threads are 16!".

Server gets busy and behaves oddly at time, i.e. it has limited resources so it breaks and does funny things

Its meant as a device for speedtesting during faults, not for day to day speed testing

In reply to a post by MrSaffron:

Its meant as a device for speedtesting during faults, not for day to day speed testing

Thanks Andrew. The reason for continuing tests is the complete unpredictability of service.
Just as a forinstance: On 20/07 speeds were Actual 2060, DL 2987, UL 785, config 3000kbps. This was an improvement on previous.
My next test was on 04/08, when the results were 3464, 4194, 787. 3500 respectively. Even better!
A couple of tests later, on 18/08, they were down to 1793, 2656, 805, 2500.
And by 29/08 they were 1383, 1746, 797,1750.
Tbb reported similar results.
This evening tbb reports DL 1906, UL 570, with bt speedtester still giving the same inexplicable messages (which doesn't afford me great confidence in bt's projected monthly load prog).

I think you will agree that, after exploring all the usual reasons for variation, it's legitiimate to suspect a fault! Unfortunately our good friends at btcare have not come up with an explanation.

I foolishly renewed my bt contract once again fairly recently.

A fault with what?

Variable speed is best tracked by logging into the home hub and keeping a log of the sync speed (i.e. speed the modem is connecting at) this can account for the wide variation in speeds.

ADSL modems are prone to interference, and they reconnect as best they can when noise is bad, which can lead to wide variations in speed.

Looking at the modem data first, is less frustrating than trying to use speedtester.bt.com

If you recently renewed contract its possible they put you over to ADSL2+ at the time if you weren't already on it - it seems that the speed tester stalls on threads 16! for a couple of weeks or so after being swapped over products.