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Will boiler/pump still work if both zone valves are closed?

docancho Member Posts: 38
I have a water heating boiler with single pump for 2 apartments. Each apt has separate zone valve controlled by separate thermostats.

I am debating between shutting of boiler completely nighttime 11pm-6am or setting a thermostats to very low temperature.

Setting to low temperature will have both zone valves closed – will the boiler/pump still work or will it shut off temporarily until one of the zone valves opens?

Thank you!


  • kcopp
    kcopp Member Posts: 3,988
    The pump can....

    Work but it shouldn't if it wired right. Why would you want to do this? Turning the heat off during the coldest part of the heating day would not be a good plan. You will get a frozen pipe.....at best.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    The law.

    I am not an attorney, but in some jurisdictions, it would be illegal to turn off the heat unless doing so still ensures that the apartments attain at least the legally specified temperatures. So even if you can technically turn the heat off at night, you might get fined for violations.
  • docancho
    docancho Member Posts: 38
    Cost saving

    Its primarily for cost saving purpose. My next door neighbor suggested shutting down as he does it.

    I have tested few nights and spoken to tenants about it. They are fine with it and temperature in apt does not fall below legal minimum during night when boiler is off 11pm-6am.

    My preference would be installing programmed thermostat with different temp for daytime/nighttime. From experience, renters play with thermostats and just open windows if too hot. I am trying to avoid this and keep cost within reasonable limits.

    I appreciate everyones input.
  • icesailor
    icesailor Member Posts: 7,265
    Set back thermostats:

    In spite of what some may say, it is my experience that with set back thermostats, if they are properly set, with the standard pre-programmed settings, people will not futz with them. If they go to work, they shut off automatically. They automatically come on before they come home. They shut off in the evening before people go to bed. If they feel cold, they will get a bigger blanket. If they are sick and cold, pushing the temperature a few degrees will make them comfortable. The thermostat sets back automatically.

    People will leave a single setting thermostat at 72 degrees all the time. A set back thermostat will change without any human input. You would be surprised at how much some people will lower their thermostats when they aren't around. With a standard one setting thermostat, they might set a 5 degree rise and when it gets half way there, they might lower it. With a clock thermostat, properly set, they usually don't touch it. If it is off during the day when they are at work, and a weekend comes where they are there, they just bump it up to a point where they are comfortable. The next morning, it has reverted to the old setting.

    I've put a lot of them in. People like them. I've never installed a set back thermostat where I had to go back and replace them with the old ones.

    And they ALL said that their fuel use went down.

    Turn off the boilers at night and SOMEONE will complain. People don't like having something they expect, taken away. There may be some little thing that annoys them but they live with it. Turn off the heat at night without their control and that little thing becomes a big thing.

  • docancho
    docancho Member Posts: 38
    Set back thermostat suggestion

    This sounds like perfect solution. Do you have suggestion on any particular Set back thermostat? I have not heard of those.

    I looked into Nest but its pricey and I see mixed reviews.

    Thank you for your input.
  • icesailor
    icesailor Member Posts: 7,265
    No nests:

    Keep out of the Nests.

    Standard Honeywell 7-days work well. I don't think you need the upgraded 7-11 day ones that work on weekends.

    I prefer going to professional supply houses to buy things. They don't want to be open for the convenience of people like me. Lowes, Home Depot and other stores stock them. You can go to Amazon.com and see ratings for them. You don't need the fanciest, just ones that work. If you have tenants, you want something Bomb Proof and idiot proof.

    They are for heating and cooling. You set it for either one or the other, Not both at the same time.

    I have one where I am in in Florida, set for AC. The standard from the factory settings are perfect. They have a digital display and give the time. They have battery back up and run on batteries. Just change them every year but they go for two+ years.
  • Ironman
    Ironman Member Posts: 6,868
    edited February 2014
    A better approach

    What type of boiler do you have? Oil, gas, cast iron, mod/con? Post some pics if you're not sure. What type of radiation? Cast iron rads, baseboard?

    A better, and different approach would be to have outdoor reset installed on the boiler. The amount of savings will vary depending on the type of boiler and radiation you have, but it should be significantly better than using setback thermostats. And the tenants will actually experience better comfort instead of sacrificing it.

    Outdoor reset will adjust the water temp in the boiler to actually match the heat loss of the building based on outdoor temp. The warmer it is outside, the lower the temp in the boiler and vice versa.

    Beware that this is something you should have a hydronics pro install and adjust. It's also not compatible with setback thermostats, but typical energy savings are at least 15%. Your actual mileage may vary.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • docancho
    docancho Member Posts: 38

    I have Weil-McLain boiler with water heating and cast iron baseboards. 1 pump for all and separate zone valve for each apt.

    Your approach seems as much bigger project and cost savings payoff in long run. any idea approx on the cost?

    I always try to keep simple as possible. in case of any heat failure, I can at least pinpoint the issue and/or fix if not too complex. with above approach, it sounds its more sophisticated where each time something does not work, I need to call licensed plumber with is very costly as we all know.
  • Ironman
    Ironman Member Posts: 6,868

    Cost is not something we are allowed to discuss on here. See the site rules.

    However, the outdoor reset control probably won't cost more than a couple of higher end programmable thermostats, labor excluded.

    As far as making the system more expensive to service, I don't see how. It's a simple control and I've been installing them for close to forty years.

    You've only stated the make of your boiler. That doesn't answer any of the questions about it. The more we know of your system, the better we can answer questions about it.

    Does the boiler have a tankless coil in it that heats your domestic water? Some pics would help.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • docancho
    docancho Member Posts: 38

    Bob, domestic hot water has separate separate boiler.

    the one we are discussing is for heating only -- its hot water heating, 3 zone valves for each apt and 1 pump for all. I am attaching pic if that would help anything.

    as for Outdoor Reset Control, does it replace current aquastat relay (as that's what currently controls water temp) or works besides it?

    is there a possibility to adjust daytime/nighttime temperate or it would be fixed temperature all the time?

    once Outdoor Reset Control is set, what happens during temporary power outage? does it continue working with same settings or it would need to be setup again?

    I appreciate your help and input.
  • docancho
    docancho Member Posts: 38
    Aquastat Relay


    I forgot to include details on aquastat relay currently on boiler and I am not sure if that play any role. it's Honeywell L8148E-1265 Aquastat Relay

  • M Lane
    M Lane Member Posts: 123
    Outside air limit switch

    A reasonable compromise is an outside air limit switch. I've put tons in on apartments. It simply interrupts the sequence of operation when the outside temp is above whatever you set it at. 45, 50...

    This way you actually don't heat much during the day. If your circulator runs off of a relay from the boiler power, you can run it through the line voltage and interrupt both the circulator and boiler. This way the boiler is still firing when conditions warrant.

    I have fixed several freeze breaks this year from folks keeping t-stats too low or otherwise limiting the boiler to save $.

    As for your OP title, pumps work on pressure differentials. They don't actually push water like a well or booster pump does, so it can just spin along with zone valves closed. But I am suspicious that there may be some strain on the motor when you deadhead like that. So its not a bad idea to have a by-pass in place.