No Pressure on Vaillant Thermoblock hot water boiler. How do I fill?

I have a Vaillant Thermoblock turbotec II. It's the German version, and I don't speak German so I can't seem to find instructions online specific to this model. The pressure gauge is at 0. Sometimes if I press the reset button (the flame with an X) repeatedly I can get hot water for a few minutes, but eventually it will go cold and the system will fail to ignite. The pressure gauge remains at 0. The minus button shows nothing. The info button shows 5.1 liters. There is no external hose for refilling. I've tried adjusting the cold water pressure as well as turning the 2 valves, the hot and cold. Nothing I do seems to affect the pressure. Sometimes I can get hot water if I keep very low pressure- the flame ignites, but it seems random, requires a lot of resetting, and eventually shuts off with failure code f28. F28 on this model, is related to lack of pressure not gas like on the newer models. Usually on reset, it clicks for a while trying to ignite and then fails.

I called a repair man, but he can't be here for 3 weeks. I'm pretty handy and would like hot water and heat today. Thanks for any help.