Public-housing tenants flooded City Hall with calls Thursday to demand more funding for repairs at NYCHA buildings, and the switchboard became so swamped that calls were rerouted to 311, said the group that organized the call-in.

“The idea was that we’d flood the mayor’s phone with calls from all the developments,” said Carmen Quinones of Community Voices Heard, an East Harlem social-justice nonprofit.

“The first phone number was rerouted. It went to 311, so we got another number we now use” — (212) 788-2162, for the Mayor’s Office of Intergovernmental Relations.

The group distributed that number at the Castle Hill Houses in The Bronx. 311 is the city’s general information and complaint line.

The group wants the city to allocate $2 billion to upgrade NYCHA boilers and heating systems — 10 times Mayor de Blasio’s proposal.

It estimated 500 people called Thursday. A de Blasio spokeswoman declined to give a tally.

“This mayor has made an unprecedented commitment to NYCHA, including $13 million to fix NYCHA heating issues this winter plus $200 million to address their long-term boiler issues,” said Olivia Lapeyrolerie.