How do I stop this? When ever I turn my central heating on the valves start to whistle. If I then ajust the temp on the rad it stops it for a while but not perminently. I live in a 3 storey building and the boiler(gloworm38cxi) is on the 1st floor. The ground floor contains 5 rads, 4 on the 1st and 2 on the 2nd. The only way to discribe the sound is that is like a whistling kettle or as if alot of water is trying to get through a small gap. The temp on the boiler seams to be fine, and I have adjusted things slightly on each rad. The boiler is serviced regularly and is only 2 yrs old. I have questioned my plumber on this but between us have been unsuccesful so far.