Pressurised system help...please!

[Luke Warm]

The red bottle you talk off is the expansion vessel .what they have tried to do is repressurise it to try and solve the problem you've been having (losing water pressure). All this aside let's get down to the actual problem.
You've said you've been doing this for awhile, seeing that your system is old the first thing I would try is ;
Take a pz1 screwdriver and remove the black taps from the valve (s) try using an adjustable wrench or pliers to turn the spindle which operates the valve.
With frequent use this plastic taps wear and stop turning the valve, even when you think it is .
The red vessel may also have failed .
How often are / was you repressurising the syste

I was thinking the exact same i thought SSE would have picked that up On the levers though!!