Plumber refund not received - next steps?

(Scotland)

A very quick question as CAB website doesn't seem to answer this.

Long story short, we had some work done on our heating system in October/November. Wasn't completed to a satisfactory standard, plumber stopped responding. We got a new person, they solved the problem; original plumber hadn't properly done what he'd said he would and had incorrectly done other bits.

We sent a letter to the original plumber requesting refund to cover costs of the additional work under Consumer Rights Act. Much to our surprise, he agreed to this with no attempt to push back. Said he would pay when he was paid for work just completed. We acknowledged agreement of the refund and reminded him that we should be paid within 14 days, as per CRA.

14 days is up tomorrow, no further contact as yet to arrange payment and, to be honest, I'll be surprised if there is any. If no contact is made and no refund appears, what's the next step for us? Would it be small claims?

Thanks in advance.