To check the pressure switch and chamber you need to open the front panel.
If you are looking at doing this yourself you need to remove the soap drawer and then take the screws out from around there.
Then open the door and you will see 3 bolts around the door. Remove them and then open the plastic filter cover and then you can open the panel from the left and it will swing open to the right.
Then you need to locate the pressure switch. Its round and has a few wires on there and a thin rubber hose.
You need to pull that hose off and blow hard down it and this will clear the pressure chamber.
Then refit the panel and retry it and see how it goes.
But to be honest on these its usually down to faulty electronics which are very expensive and as you say probberly not worth it on a 14 year old washer.
If you need anymore info just get back to me.