Problem with EGB losing water level


We have a problem with one of our EGB’s onboard, it will randomly lose water level and it is very difficult to recover,

Even with the emergency filling valve open, the automatic filling valve open, the level will not increase until we decrease engine load to approx 50%, but then when we increase load back to standard load (about 85%) we have to leave the emergency filling valve open, and even then the level will slowly drop,

We have checked blowdown valves and can confirm they are not passing.

There is no trend as to when this happens, it will happen at any time, even when at steady load with no change. And sometimes it will not happen for weeks but then will consistently happen for days

The only thing we have noticed is the steam pressure is higher than the other egb’s at 8 bar compared to the others which are 7 bar. Weve reduced the set point to 6 bar but this has little affect. The feedwater pump is in good condition with a good discharge pressure.

Anyone have any ideas as to what it may be?

Are exhaust temps going into that EGB in line with the others?

Has anyone looked in the exhaust trunk when it’s not running (but has a fill valve open) to make sure there’s no internal leaks?

Guessing both of those things have been checked, but didn’t see them mentioned in the post.