Combining them is one possibility, as is your special the semi sealed. I personally would like to pressurise. However, we know what the problem is now and why the hydrogen is being produced, what the OP needs to do now is have a proper power flush and adequate inhibitor added. A power flush though is not a half hour job, its a day minimum and thats for small domestic dwellings. Once this has been carried out then the OP can consider how he approaches the outcome. Whatever method above choosen I would suggest a suitable filter for the system and appropriate means of air removal, free air, microbubbles and dissolved gases.