I have a similar question - I have a Climate Master HVAC system (actually two of them in the condo) which distribute heat via the building's hot water system. Connecting the Nest has been a challenge but have made progress, got the system to produce heat but while the hot-water solenoid activates properly on schedule and (under geothermal configuration) the fan does not initiate, requiring manual activation. This setup produces heat but it is not ideal since the fan does not activate with the solenoid. I've attached pics of the original thermostat wiring block, and schematics and the Nest wiring block. Hope you can help and thanks in advance.
On more note: the original thermostat was right beside the HVAC unit (not a great idea) and I had it moved to a more appropriate location meaning a new run of wiring was added on, with the HVAC Brown going to White to the thermostat block. Additionally the HVAC unit has Orange going to Blue wire, and a Gray going to Green wire. The rest, Red and Yellow are straight through,
