On Sunday, 14 July 2019 19:00:45 UTC+1, wrote:
It is recommended not to have 3 or more wires coming out of a MCB or RCBO..

I didn't even know it was permissable to spur of the circuit origing, until I looked it up in the regs. Good point about the 3-wire aspect.

In fact, I would use a RCBO for 3 very good reasons but you would have to wire the RCBO upstream of the RCD. (The main one being the boiler still continues to work stopping the house from freezing if the main RCD trips so you don't come back to a flooded house. The second reason is if the washer develops a water leak, it does not take out the RCD and affect half the house.

This is a high availability CU with four spare non-RCD ways so I might well move it onto its own RCBO. I note Andy's point about a boiler and washing machine sharing the same RCD/RCBO protection however I wouldn't be running the washer whilst out/away and, if it did start causing trips I just wouldn't use it until fixed (I am assuming the most common failure mode would be when it is running).