Digital TV service Freeview's website crashed on both Tuesday and Wednesday.
More than 18 million Freeview viewers were required to retune their set-top boxes on September 30, following an upgrade to the digital TV service.
Freeview's helpline was also receiving 200 calls a minute from consumers seeking advice.
The upgrade will give more viewers access to Channel Five and well as ensuring High Definition (HD) broadcasts can eventually be rolled out.
However, once the upgrade has taken place, viewers that can currently receive the channel will find they are unable to access it unless they re-tune.
On the morning of the big retune a site to guide viewers through the retuning process repeatedly crashed. Freeview admitted the website crashed because of high demand, but claimed that it was working "intermittently".
More than 20m digital TV set-top boxes need to be retuned to maintain access to TV and radio channels. 20,000 older set-top boxes will cease to work.- including Daewoo models DS608P and SV900, Labgear DTT100, Triax DVB2000T and Bush IDVCR01.
The BBC reports that hundreds of people with Freeview complained after losing some channels when they tried to retune their set-top boxes and TVs.
PC Advisor readers are largely reporting trouble-free retunes. Add your Freeview retune comments here.
While many homes gained Channel 5 it is estimated that 460,000 households are expected to lose access to ITV3 and ITV4.