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Ok, the model you gave me is for a control unit not a boiler or water heater. I take it you have an indirect fired water heater? I need boiler and water heater model numbers. Also when you say you lost pressure, where is that? in the heating system/boiler or coming out of your hot water faucet?
Take as much time as you need. I'll be here for another hour at least before I take a break
Your pressure readings indicate to me that you're in Europe. I'm in the States. We do things differently here particularly when it comes to adding pressure to the system. I'm going to opt out and one of my European colleagues should pick up your question. If you don't get a response in a reasonable time I can try to assist you but I'll need pictures of your system. I am quite familiar with Buderus products but this is more of a system issue. Please don't respond to this answer(even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer. if you don't get a response in a reasonable time then get back to me via this thread.