Hot water but no heat?

My friend's house has a hydronic heating system that uses a boiler and indirect water heater. A few weeks ago, the air separator sprang a leak because of rot. She shut off the boiler and closed valves until it stopped pouring out water. I replaced the air separator and vent, opened the valves in a logical order, and got the boiler restarted. Since then, the heat has been wonky at best, but the hot water has been fine.

As far as I can tell, the entire house is a single heating zone (there's only one thermostat), but she has told me that the heat on the second floor has never worked; after the new air separator, when the heat has worked, the second floor has gotten unbearably warm. There is a Taco zone switching relay at the boiler with two LEDs–"Power" (red) and "Zone 1" (green)–the "Zone 1" LED has been off since the problem occurred; it was always on before. I haven't taken the time to trace all the wiring, but the relay is fed through a number of other sources, and seems to have a control circuit to the water heater (two small diameter wires).

The basis of my question is, what about changing the air separator could cause the heating system to fail? I assume air in the system, and I haven't pulled open the baseboards to see if there's a way to bleed them, but why would it work sometimes? (It seemed to work when she decided to set the boiler temp to 220º) The plumbing in this house is a mess, and I've opened every valve that I thought might release trapped air.

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  • 8 months ago

    Did you properly burp the system to get out any air pockets that may have occurred when the air separator failed

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