some radiators are not getting hot... what gives??

Chris B

i just noticed, now that it is getting cold, that not all of my radiators are getting hot. 1st floor, 4 out of 5 are hot, i do have some(bedrooms) shut off on 2nd floor, as the heat rises enough to make them toasty. i did notice some water on the floor under the outlet for the releif valve. plan on flushing that this weekend. probably replace it... have I lost that much water that the system is running out?? also how can I tell if the circ pump is working? it never makes any noise...
thanks from a newbie...

Chris