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Prog. Thermostats w/ gas boiler/hydronic radiators

sscerberus
sscerberus Member Posts: 7
Hello,

I'm looking for professional opinions as I currently have a gas boiler / hydronic radiator heating in a 100+ year old home. Currently, I have the old round dial mercury thermostats. It's a 2 wire (Rh, W1) system. I have a Burnham series 2 gas boiler 15+ years since it was installed (Recently moved into the house and there was no paperwork with it, but the last service noted on the side of the boiler was 15 years ago).

My question is that I have been told by over a dozen different heating and cooling technicians in the area that a programmable thermostat should not be installed on a gas boiler / hydronic radiator heating system... End of story. However, every company I talk to that makes thermostats (Nest / Honeywell / EcoBee) have all told me that is either a lie or an old wives tale and their products will work fine. So which is it?

Little back story. 4 months ago I purchased 2 Nest thermostats as I have 2 zones (1 for each floor) and it was never really working properly because I kept getting power loss errors. I figured it is because I do not have the infamous C wire installed, but Nest kept saying that does not matter and their system will run fine on 2 wires only. Nest finally agreed to pay for a tech to come and look at the system, and the tech flat out said the Nest should not be installed. He explained that (1) due to the modulating needed for the boiler, the nest was preventing the boiler from running in a low mode, and instead always commanding the boiler to operate on high which was resulting in overheating the water, and causing the limiter to kick the system off. So the room temperature could never be achieved because the water temp was always stopping the boiler from radiating enough heat to bring up the room. It was also causing constant over cycling where the nest was just constantly trying to run to achieve that room temp. Nest of course said that was not the case, but eventually caved and allowed a refund.... So I'm back with the old Mercury thermostats. Afterwards I decided to call other technicians in my area and they all agreed without even looking at it that any programmable thermostat will do exactly that, and I can only use a non programmable thermostat.

Does everyone agree, or is that something that may have been true at one point, but newer thermostats that have come out have improved and found a way to work? I realize I will have to install a 3rd wire for C and I'm fine doing that if I can actually use a programmable thermostat.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,071
    No good reason not to use a programmable thermostat. Just don't set the setback too deep -- 3 degrees is enough. I prefer the Honeywell VisionPro series -- there are a number of models, many of which are battery powered and will work fine with just the two wires.

    Personally I would not have a Nest in the building. If you do want to use them for some reason, you will need to run the C wire or they will never work properly.

    May I ask what you don't like about the round mercury thermostat? Other than not being programmable -- which can be solved by manually turning them down at night and up in the morning -- they are bulletproof.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • sscerberus
    sscerberus Member Posts: 7


    May I ask what you don't like about the round mercury thermostat? Other than not being programmable -- which can be solved by manually turning them down at night and up in the morning -- they are bulletproof.

    Not that I do not dislike it, I do see benefits with going with a digital thermostat as it can be more accurate...

    Mostly I just want to be able to control the temp without physically having to go to the thermostat. In bed is the perfect example. In the middle of the night I often wake up too hot. I normally have the temp set at 68... and would like to back that down to 66. But then have it go back up to 68 just before we wake up.

    I do not care about the energy savings of newer thermostats, as I believe the amount of energy used to reheat the water vs just keeping the water at a constant temp just about cancels each other out. If I were to have a forced air system... then I would understand the benefits of "setting back" the thermostat when I'm away.
  • sscerberus
    sscerberus Member Posts: 7


    BTW, all thermostats are just switches and a switch cannot command the boiler to operate in low fire, high fire, or any fire. It just commands the boiler to start.

    Yeah, that was my impression as well... but as I said, the tech said in his diagnostic that the Nest was killing the power preventing the boiler from being able to properly keep the water temp regulated. I don't really understand how the nest would be any different then the Mercury thermostat, unless something in the internal wiring of the nest opens a circuit killing the flow of power in some manner.
  • sscerberus
    sscerberus Member Posts: 7

    Never underestimate the creative abilities of a "tech" when he doesn't understand anything about which he speaks.

    The term "male answer syndrome" comes to mind.

    It's a sad commentary today. A race to the bottom.

    I agree... but at the same time when over a dozen techs in the are tell me the same I have to wonder if they are right... even though it doesn't make sense to me, but I can't even find anyone who will install one on my system.
  • CMadatMe
    CMadatMe Member Posts: 3,085
    Umm... Series 2 is not a modulating boiler and the Nest or any Stat is nothing more then a switch that tells something to open (zone valve) or run (pump). What's that have to do with the boiler operation?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jamie Hall
    Jamie Hall Member Posts: 17,071
    A Nest, unhappily, is not just a switch, nor even a programmable switch such as, for instance, any of the Honeywell lines. It is a computer, and hooked up to the 'net -- and Google, in Kalifornia. There is no way for the homeowner -- or service personnel -- to predict what it is going to do, nor when.

    Your service people may not know why they don't want to install one, but they know that they are trouble and they don't want to be part of it. I don't blame them a bit.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England