The flow and return valves are part of the central heating circuit, the two grey valves are part of the filling loop. So not the same thing.
Both grey taps need to be in the open position. I assume you have not touch any other valves than these two.
If you are getting hot water, that would suggest you have a water supply to the combi-boiler and the the boiler is pressurised enough for it to fire up.
What is the pressure gauge reading and have tried bleeding the radiator you have attempted to fill.
If you already gave 0.7 bar, it is possible that this is enough for boiler to fire up, but ideally wants to be about 1.2bar. You should hear and feel water running through the loop when both valves are open, but sometimes the fill is slow if an additional external filling loop has not been installed and the gauge will only move up slowly.
Also check that there is no water leaks on system or boiler that is stopping the pressure from rising.
Extract from boiler manual:
4.5 Filling the Sealed System
NOTE: The water pressure at the boiler must be at least 1.2bar to enable filling the boiler to a minimum pressure. If not pressurisation must be carried out by an alternative filling loop. The boiler has a built in filling device, see diagram 4.2. A pushon extension is supplied in the loose items pack to ease access to the filling device tap. This filling device is designed to enable the re-pressurisation of the system in the event of loss of pressure. It is not intended to be used to completely fill the system. If so used, it may take a long time to fill the system. To fill the system quickly provision should be made to include a proprietry filling loop external to the boiler. Suitable external filling systems are shown diagramatically, see diagram 4.3. The system should be pressurized to 1 bar, indicated on the digital display with no heating demand.
