One of my radiators (bathroom - Twinfast valve - Worcester Highflow Heatslave Boiler- 22 years old) makes a noise as though loads of air is getting into it - especially after the boiler diverts back to C/H after a bath / shower.
However, when I check the bleed valve there is never any air.
What is going on? It sounds like loads of air is entering at times.
How much water are you taking out the bleeder when you check it? You will also have to keep topping up the boiler pressure after you have bled the system, how is this done, and to what setting on the gauge are you choosing? What diameter of pipework is feeding this radiator and does it have any tight bends near to the radiator?
Sometimes a radiator can just do this type thing and there are many causes why it does. A simple piece of plumbers thread tape had us going crazy when our system was first installed. A little bit of the tape had slipped over the edge of one fitting and was acting like the reed on a clarinet when the water moved through the pipework. Took us two weeks to find out where it was, because the sound also travelled along the pipes.
If there is a little imperfection in the construction of a valve, or on the radiator itself, it can cause the water to swirl around inside. This can sound like air is being forced through the system. With the boiler Stat' turned off, try running the system and put your ear on the area you think is causing the problem. I ask you to turn the heat off to do this, because I don't want you in casualty with third degree burns to your face.
Listen to the water flow around the system and, if you are listening carefully enough, you might actually be able to hear exactly where the sound is coming from. It may actually be at a bend under the floor Etc. Or in a fitting further down the line from the radiator the noise is most noticeable at.
Your system seems to working OK otherwise, or you'd have mentioned other faults with it. So it seems like it is not causing any major problem and is just a nuisance noise. Unless it gets worse or other symptoms appear, I'd advise you to forget all about it.
Hope this helps a little.
My system is gravity fed.
I will try running it cold - but I suspect it may be related to the temp of the boiler. As I say - there is never any air. It sounds a bit like air being forced through a tight space. Will try opening lockshield full to see what happens as well.
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