diagnosing heating system noise

[top of the hill]

hi
Could anyone suggest why, suddenly, I've begun to get a noise like rushing water through several of my radiators when the heating is running. Its the kind of noise one gets when all the lockshields are wide open, only I've not touched any of them and then noise seems to have started all of a sudden.
I have a combi sealed system, with modern trvs on all the rads except the bypass. Don't know if its related but I've very recently had a problem with lowering system pressure, which I've been struggling to solve, I did find I had to recharge to expansion vessel which did stop the clanging air type noise I'd been getting, but not this whoosing noise.
Only other thing thats new is that the weather had taken a turn for the worse so the heating is on more frequently

 

[bengasman]

Could be the trv's are noisy, what brand are they?
Lockshields should never be fully open, but when they are, you don't hear them

 

[top of the hill]

trvs are honeywell, and have been fitted for about a year, noise has only beeh happening a week or so

 

[tommyl18]

could it be air in the system if you are losing system pressure

 

[Goldberg]

Was the system converted from an OV system?

How old is the pipework?

 

[top of the hill]

could it be air in the system if you are losing system pressure

I was getting air in, I added some leak sealer out of desperation. The falling pressure has stopped - although it was only ever quite slight. I no longer seem to get any air, or at least I can't bleed any out.

The noise sounds a bit like kettling - but as I say its only a few upstairs radiators. I'm completly out of ideas.

I've lived in the house about eight years, and its always had a combi. I changed the pipe work upstairs last year at the same time I upgraded the trvs

 

[BingoBongo]

could it be air in the system if you are losing system pressure

I was getting air in, I added some leak sealer out of desperation. The falling pressure has stopped - although it was only ever quite slight. I no longer seem to get any air, or at least I can't bleed any out.

The noise sounds a bit like kettling - but as I say its only a few upstairs radiators. I'm completly out of ideas.

I've lived in the house about eight years, and its always had a combi. I changed the pipe work upstairs last year at the same time I upgraded the trvs

you may have been getting air in due to the leak or corrosion.

adding leak seal may have done more harm than good,if its kettling that may be down to the leakseal gunging up in places it shouldnt

 

[top of the hill]

yes, thats why I added it reluctantly, but I couldn't find any hint of a leak. do you think I should drain fully down and start again?
although, that being said, my radiators are still getting hot, so no evidence that way of a blockage.