Websites telling TV viewers how to re-tune their digital Freeview TV boxes have crashed under demand.
Designers of the flu advice website admitted they had underestimated demand and they were forced to quadruple capacity to keep the service going.
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The Freeview service was upgraded this week to give more viewers access to channel Five, but thousands of boxes had to be re-tuned after frequencies were changed.
Freeview's website and another site designed to tell users how to retune boxes, crashed yesterday because of a spike in demand, according to the Telegraph.
The Freeview telephone helpline was also hit by up to 200 calls a minute from viewers wanting to know how to restore services.
More than 500,000 homes will be able to receive Five on Freeview for the first time after the upgrade, but about 460,000 households are expected to lose access to ITV3 and ITV4.
Freeview estimates that the upgrade, which will also give access to high definition services, will require user to re-tune 25 million TVs and set-top boxes.