My wife's Technivorm exhibited exactly the same problem, i.e., light comes on, no brewing. Here's something you can try.
Remove the lid to the water tank. With the brew pipe facing toward you, there is a perforated piece of metal on the right hand side. This is held in place by friction, with four pins going into mounts. Get yourself something that you can hook under the shield - a bent piece of wire will do, a paper clip might be too little. Now gently remove the metal piece, working it alternately on each end if necessary. The thing here is to NOT bend the seating pins.
Under the metal cover is a float, hinged on the rear side. Look into the float chamber and see if you have something preventing the float from operating freely. My wife's machine had two coffee beans in there (I have no idea how they got in there). Remove any debris keeping the float from operating. Replace the metal cover, noting that the unperforated end goes above the float hinge at the rear.
This got my wife's machine working again, and did not require the removal of any screws - which is not to say that any number of them weren't removed by her during the exploratory phase. The water tank isn't even held on with screws, it's held on with star bits. All I can say is thank god she didn't get hold of a Philips head screwdriver to try to get those puppies out.
Think how stupid you'd feel if you drove your machine 30 miles to the coffee machine repair guy, and this was all he found...
Rancilio Silvia, Hario v60 01, Rancilio Rocky,
Behmor 1600, FreshRoast SR700 (soon)...
...and my wife drinks K-cups (sigh)