I read that "radiant" (ie. Heat radiates from hot water) systems need to be bled, or purged of air, usually radiators are bled once or twice per season, or as needed.

I've never done mine, but now suspect I have to because of the symptoms explained below, and I want to do it myself.

The bedroom zone has been programmed to kick in at 5:50AM before I get up at 6 and go back down at 7 when I leave for the day.

I've been hearing increasingly more and more sounds from the bedroom rad in morning before I get up and I'm worried something is wrong. It would be the furthest upstairs rad from the downstairs boiler.

In the 3.5 years since being in my 10 year old house with an oil fired boiler, I've heard a few minor tick tick ticks, and more recently a slight hiss- all things I ignored in my layman's way, thinking its fairly normal. Today was the most disturbing sound- that of running water, like a tap was on and it was running down a drain. No signs of leaks.

There is nothing I can see on the finned rads to bleed air. The only "air bleeding-looking thingy" I see is on the top of the regulator just before the 4 "zone controlly-looking boxes". I won't touch it until I find out more about how to do it.