E.ON, Scottish Power, British Gas and SSE websites have crashed, according to customers attempting to submit their meter reading.
A message on the British Gas website told customers it was facing "some technical issues we're trying to resolve as quickly as possible". The message said customers could still submit readings but warned it could take "a little time to update your account with the meter reading you provided today".
EDF Energy's website also reported problems, apparently as many people tried to submit their meter readings on their account. The main page of EDF Energy was working, but when customers clicked through to the MyAccount page they were unable to log in.
READ MORE : EDF, British Gas, Octopus and E.ON energy tariffs as customers face soaring prices
A message on the page reads: "Sorry... We're carrying out some essential maintenance work on our site. We'll be up and running again soon." E.On also seemed to be facing issues with letting customers log in to their accounts, while customers of So Energy reported that they were unable to either log in or get through on customer helplines.
According to Downdetector, E.ON, Scottish Power, British Gas and SSE have gone down.
Gillian Cooper, head of energy policy at Citizens Advice, said: "We'd recommend sending meter readings to your supplier ahead of the price cap rise on 1 April. This means your energy company will have an accurate picture of your usage before higher rates come in.
"If you're struggling to pay your bill, speak to your energy provider as they have to help you. Citizens Advice can also provide you with free, independent support."
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