I'm new to hot water heat - had a beautiful one-pipe steam system in my old house that Dan's books and wisdom helped me keep running in tip-top shape for 20 years. Bought a new house, and it has hot water heat, two zones, with a circulator on the return. There are two TACO zone valves on the supply side, and (obviously) two thermostats, one for each zone. In general, the system works well enough, but here is my problem:
The larger zone seems to work as intended - when the thermostat calls for heat, all the radiators on that circuit get hot, and the radiators on the other zone do not. The large zone has 7 radiators. All is well.
The smaller zone also fires as intended, BUT, after a few minutes all the radiators on the OTHER zone start to get warm. This doesn't happen right away, and the two radiators (there are only two radiators on the small zone) on the active zone are really hot before the radiators on the OTHER zone start to warm up. Eventually, all the radiators in the house are hot but only the small zone thermostat has called for heat.
When I bought the house, the valve for the two largest radiators in the main zone were shut off, and the previous owner couldn't figure out 1. why the radiator in the den didn't get hot, and 2. why the thermostat for the big zone (located in that same den) didn't "do anything". It does, in fact, work, but given how the system works, it appears that the thermostat is redundant. He wasn't a heating man...
I've done some troubleshooting, and here is what I know:
- The small zone is farthest from the boiler, and only has two smallish radiators on it.
- The zone valves are not leaking externally.
- The electrical system seems to be working correctly, I checked with a multimeter and the valves are energized only when their thermostat calls for heat.
- By checking the manual opening levers on the valves, it seems that the valves are opening and closing according to their thermostat calls.
- The large zone has radiators on the first and second floors of the house; the small zone has radiators on only one floor and it is positioned on an intermediate floor INBETWEEN the 1st and 2nd floors.
So...I'm confused. I'm guessing that the large zone valve may start to leak when the system gets hot? Or maybe hot water is going through the returns even though the supply-side valve is closed?
As Dan has suggested, I am keeping my hands in my pockets for now and just looking. But I would love to understand why this is happening and fix it. Any wisdom that you all can impart would be appreciated.