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Two zones, if one TT calls, both zones get hot...sometimes.

RickCiervo Member Posts: 3
edited October 2014 in Gas Heating
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.

Thanks all.


  • RickCiervo
    RickCiervo Member Posts: 3
    Maybe this?

    The small zone is all the way at the end of the line. Both zones share a single return and the hot water return has to go past all the other radiators in the other zone on its way back to the boiler. If the big zone is off, the radiators are cold, but there is hot return water flowing past their return connections. As Dan points out, there will be some Delta T in the return line, but going the wrong way - the radiator is colder than water in the return line.

    In this case, would the hot return water rise up the return line to the radiators, effectively making my big zone a poorly-built one-pipe hot water system? This might explain why it takes a while for the big zone to start getting hot once the little zone is cooking away.

    If this is correct, then the only solution would be a check valve in the return lines for each of the big zone radiators, or a possibly a completely separate return for the small, far away zone that connects close to the boiler, possibly with a check valve there for the main zone return.

    By the way, I don't think the house had separate zones when it was built - it looks like the second small zone was added at some point (at least to my untrained eye)
  • Zman
    Zman Member Posts: 7,446
    I am thinking that either the valve is not seating completely or the circulator is pushing it open. What circ is it?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icesailor
    icesailor Member Posts: 7,265
    If they are Taco 57* wax motor valves, just because you can pull and operate the levers doesn't mean they are working properly. If they are very hard to push down to the point that it hurts your finger. Spray it with WD-40 and get it so you can easily open and close then handle. If the valves are side by side, both levers should reach resistance at the same time, and go to the same bottom at the same time.

    Turn off the power to the valve power heads by taking the top or #1 wire off and waiting for at least 3 minutes. This is absolutely critical. You can NOT have a call for heat when the valve heads are off the body's. Look at the flat black plate where the plunger sticks through. If there is any rust of anything around or on the black plate that will cause interference with the plunger, the valve might occasionally not completely close. Spray it with Kroil. Take a large pair of water pump pliers large enough (14",or larger) to span the bottom of the valve and the top of the plunger, sticking through the black metal plate. Take note if one is sticking up higher than the other. Operate the plunger with the pliers. Don't beat on it. Just "romance" it carefully. If it was sticking, and you get it free, put some synthetic grease like SuperLube Synthetic Grease. If it starts working, you're set. Do both valves.

    There could be some crud in the seat. You can replace the valve parts without unsoldering the entire valve. If you ever get to that point, ask. Its easy but you have to use a method. Don't ever take the 4 screws holding the plate down. Spray the 4 screws not so you can get them loose and out. If you can't get the screws out, you have to change the entire valve. A serious PITA. Do NOT take out more than one screw at a time. Unless you know, and have all 4 screws operating and free.

    Also, check the piping of the zones. Someone who just posted, is correct in what he said. He just didn't mention the sticking plunger in the hold down plate. Which I am personally quite experienced with.
  • unclejohn
    unclejohn Member Posts: 1,830
    Pictures of piping would help. Sounds like you are getting some flow where you don't want it. Some flow checks may help.
  • Zman
    Zman Member Posts: 7,446
    Did anyone else here the Crickets?.....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Don_197
    Don_197 Member Posts: 184