Yay! Heater works again! Turns out air got trapped in my radiator blocking the hot water. Maintainance guy told me it's because I'm at the top level at the end of a heating-string. Ah, that makes sense indeed.

Leakage stains are nothing to worry about, it's from the snow melting, but it won't get worse that that. Next spring the roofs will be renewed and it won't be a problem anylonger. As soon as that happened maintainance guy will paint my ceiling. :)

I is happy camper again. :D