Central Heating gets aerated

[csauk]

Hi
Can anyone please advise on a possible cause of the following problem with a newish fully-pumped, open-vented system - Vaillant ecomax pro boiler - in a small 2 bed semi?

With either CH only, HW only or both, from a cold or coldish start, when the flow temperature reaches around the 60 degree mark a rushing sound of aerated water begins. It reaches a peak as the temp increases to maximum and then gradually subsides though the boiler maintains the maximum temp.
If the thermostat switches the boiler off when the sound is at its peak, it subsides almost completely in less than a minute though the pump continues to run.
The system has slightly more than 0.5L (half a pot) of X100 Inhibitor added.

Any suggestions gratefully received.

Craig

 

[DP]

I would suspect the system is dirty and what you are hearing is form of kettling.

 

[csauk]

I would suspect the system is dirty and what you are hearing is form of kettling.

The sound of aerated water can be heard mostly in the airing cupboard where it sounds like shingle in the surf at it's worst. The boiler does kettle a bit while the rushing sound is happening but that stops when the rushing stops.

 

[JackF]

I would suspect the system is dirty and what you are hearing is form of kettling.

The sound of aerated water can be heard mostly in the airing cupboard where it sounds like shingle in the surf at it's worst. The boiler does kettle a bit while the rushing sound is happening but that stops when the rushing stops.

I have the same sound coming from my pump and it is sucking in air but when I turn the pump speed down to the lowest It stops the surging noise and the system remains clear of air after purging.
The problem with this is it takes a lot longer for the rads to heat up and some stay cold at the bottom.
Any ideas
JackF