cold down stairs hot upstairs - Help

Hi complete newbie for central heating

can someone point me in the right direction please.

I have a ideal mexico boiler a pump behind it to metal boxes with little levers under them

and a thermostat that goes round the actual water container boiler thing (No laughing i know its not the right terminology)

Radiators only heat up stairs and not down. last winter it worked intermittently. I turned it on last week and the same has happened.

Is there a number of things I can try before calling out an expensive heating engineer.

Yes
check if your pump is working? hot water rises to upper rads but wont pump down.

If working close all the upstairs lockshields down then open just half a turn the water wip push downstairs
jay...

sorry some silly questions

how do i know if the pump is working ?

what are lockshields (Bleeding taps?)

when you say open half a turn the ones up stairs or down starirs


many thanks