Starting Point: Basic Oil Boiler system
We'll start with a simple oil fired hot water baseboard system comprised of very common components. This is a plumbing schematic for the initial system before the wood boiler is added:
In this simplified example, There is a system with three heating zones: Top floor, Main floor, and Domestic Hot Water. Pipes carrying hot water are shown in red, and cooler water is in blue. In this simplified diagram, many components such as air separators, isolation valves, and makeup water connections have been omitted for clarity.
When there is a demand for heat, the built-in oil boiler controller will turn on the circulator, and if the boiler is not at temperature, it will turn on the oil burner as well. The circulator moves water through the oil boiler where it's heated to around 180 degrees, then through any open zone valves and associated baseboards or heat exchangers, then back to the circulator.
From a controls standpoint, the system is also straightforward. There are two thermostats and an aquastat. Each of these is essentially a temperature controlled switch that closes when the temperature drops below the setpoint. They are each wired to a zone valve motor so that the zone valve opens when the contacts are closed:
Each zone valve has electrical contacts (limit switches) that close when the zone valve is open. These contacts are connected to the oil boiler controller so that if any zone valve is open, the oil boiler is signaled that there is a heat demand.
Control Block Diagram
This is a very typical system, though of course there are many variations. A common variation is for each zone to have a circulator instead of a zone valve. In this case, there is no circulator for the oil boiler itself. Systems may not have indirect hot water heaters, or may heat using forced hot air rather than baseboards.
The process for other system architectures is similar. Study the diagrams above and make sure that you understand how the system works.