Noisy radiators, c/h switched off and motorised valve proble

As of late I can hear water gushing through the upstairs radiators, which seems to occur a few seconds after I hear a gushing noise in the pipes/tank in the loft.

When this occurs the thermostatic valves on the rads are turned off, as are/is the central heating timer controls and the main room thermostat.

Not sure if the following is relevant but...

1) I have bog standard, open vented stored system with a cylinder in the loft.

2) The boiler recently locked out, which seemed to occur after the cylinder was drained (the hot bath tap was left running for an extended period by accident). The PCB indicator light on the boiler suggested a flow fault and I got the boiler working again by setting the motorised values to manual.

3) I think that the motorised valve on the flow pipe coming out of the boiler is faulty (motor gone). I assume the valve is open because the radiators get warm if I turn their thermostic controls to max with only h/w selcted "on" at the timer (and room thermostat turned right down).

4) The feed/expansion tank in the loft is 3/4 full of hot water and there is a lot of rusty coloured discharge sitting in it. It also gurgles.

Does it sound like I have major plumbing problems and will I need a plumber to sort them out?

May have sludged/blocked pipes
may have poor pipework design
may need a bypass
valve motor failing wouldn't leave it open, but shut
header tank water level is too high

may need a heating engineer!