@kezo as far as I’m aware Legionella only appears if you have a tank. It would be good to hear how you get on with your “weather compensation kit” and just as an aside how easy is to fit?
Yes a combi is classed as low risk mate.
The kit is simple to fit, the Baxi one clipped onto the external flu, I run the cable outside the flue and into the house and its just 2 wires connected to the boiler PCB.
I did watch a video of a plumber running through the twin wall flu and past the heat exchanger, which (a) the risk of the cable melting is quite high (b) It would reqire removal of the flu and I’m not gas safe qualified
A stand alone unit would fix to the wall, and the cable taken to the boiler PCB as above.
Taking into acount I’m qulified it was easy as for a DIY install it isn’t rocket science with 2 wire connected to the low voltage side of the boiler PCB, though you would have turned power to the boiler anyway.
If you plan to go ahead, let me know your boiler model and I’ll tell you the two terminals you need to connect to.