Verb
get on like a house on fire (third-person singular simple present gets on like a house on fire, present participle getting on like a house on fire, simple past got on like a house on fire, past participle (UK) got on like a house on fire or (US) gotten on like a house on fire)
(simile) To immediately start a good relationship with someone.
Those two met last Saturday at the party, and because they were both into juggling they got on like a house on fire.