Old Gas Boiler replacement - STILL not viable?

BUFF

fuzileer said:

Control communicating at bus level is a bit beyond me I'm afraid but I can look into this.

Worcester Bosch use a proprietary eBus called EMS. Afaik the only controls that can communicate at EMS level are WB's own (& possibly other Bosch group boiler companies' e.g. Buderus & Junkers as I suspect that they all share basic technology). There are devices that can translate to similar Opentherm controls (it's a legal requirement in Holland) but iirc WB can get a bit picky about warranties if you have gone down that road.
This might be worth a read but eBus/EMS level control with load/weather compensation should be worth a few % (probably £100 per year at your level of consumption/April 22 cap pricing).
https://theintergasshop.co.uk/content/186-is-opentherm-worth-it

p.s. the 24Ri is rated at 98% efficiency for a 30% rated output/low flow temp regime v your G-rated being under 70%.