Our boiler is not giving us hot water. We had a company come out twice to "repair" this in the last year and we're really hoping not to spend $500 again. I think that I have some idea...
On the gauge that reads "bar," the water level is below 1. I need to know how to replenish water into the system and I think that will do the trick.

Since you did not bother to post the EXACT model number for your Baxi I took a guess. Below is the manual for the series 330 unit. Naturally it has the BAXI caution that states ((It is the law that any service work must be carried out by a competent person)). If you are that competent person then the manual below is for you.

http://www.blueridgecompany.com/documents/Baxi_LunaHT330.pdf