That level of fluctuation is normal in the wider sense with broadband.

I have not had a great deal of hands-on with Infinity yet but generally with broadband your speed is being monitored and adjusted between the exchange and your router by a piece of software at the exchange end.

It attempts to optimise the speed at which your particular line will operate in a stable fashion during a "training period". It reads all sorts of things including signal strength and background noise which indivudually will have a direct bearing on your line speed and will make adjustments automatically.

Initially this can mean significant fluctuation but those fluctuations should settle down as it fine tunes the settings. This so-called training period can last between 24-72 hours by which time you should have a real sense whether your installation has been successful.

As a cast iron rule you should not power down the router during that training period. You may see it dis-connecting and re-setting itself during that period but that is perfectly normal.

In most cases this settles down quickly with line stats that are entirely acceptable.

BT engineers tend to dismiss enquiries about speed for the first 5-10 days on the basis that they may intervene if the automatic software does not bring about the required result and issues warnings to them.

Examples of problems that could prevent good line stats are poor connections or damaged cables and of course, if you are FTTC, the last few metres from your nearest cabinet are still the original copper cables.

I trust your wi-fi re-tuning exercise wasn't too onerous - and if you have a new Homehub 3 - I have been very impressed by its three dimensional transmission rates.