get on like a house on fire可不是“房子着火”，而是“一见如故，情投意合，一拍即合”。

【例句】
I was worried that they wouldn't like each other but in fact they're getting on like a house on fire.
我之前还担心他们会合不来，实际上他们却一见如故。

We got on like a house on fire. I wasn't sure my little brother and my boyfriend would like each other, but they actually get on like a house on fire.
我之前不确定我弟弟和我男朋友会不会合得来，但实际上他们一见如故，相处得很好。