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normal duration & temperature range from beginning to end of a heating cycle?

ThisSemiOldHouse Member Posts: 15
edited November 2019 in THE MAIN WALL
I have a Weil-McLain Gold CGi Series 2 gas-fired water boiler that I only recently have begun to understand how it works (NOTE: am a relatively new homeowner; the house is three floors plus basement, and heat is distributed via several older cast-iron radiators and baseboards). Last week I joined this site and I've asked a few questions here about specific points of the aforementioned boiler's operation, but it occurred to me that I'm still not familiar some very basic things about it (or about hydronic heating systems in general). Chief among these would be that I don't actually know what gauge readings throughout a typical heating cycle would constitute "normal" (or optimal) operation. So I thought it might be a good idea to ask about that. Here are some basic points I was wondering about:

(1) Is there are a ballpark duration that a boiler heating cycle should last? (I realize that this could depend on how cold or warm the weather is at the time, as well as if the heating was just first switched on after being off for months. But assuming that the heating system has been on a for a while, and the boiler has cycled off for, say, an hour... is there a particular number of minutes that it should ideally be running before it cycles off again?)

(2) I've read on this site that the low temperature and high temperature during a heating cycle can be adjusted via the aquastat. Until now, though, I haven't figured out where that component is on a Weil-McLain Gold CGi Series 2 boiler, so whichever temperature settings existed when we moved in here, are what still exist now. Over the last few days (during which the weather has been in the upper 30s, and the thermostat has been set to 70), I've been writing down the temperature values that have been displaying on the boiler's gauge to get an idea of how the thing is performing. In general, after the boiler has cycled off for 45 minutes or an hour, the temperature falls to around 85 or 90 degrees, and then when there is a call for heat, the heating cycle lasts for about 8 or 9 minutes, and the boiler temperature ultimately rises to around 157 degrees and then cuts off. Are these temperature values normal? And if not, how can I make any necessary adjustments to either the low temperature or the high temperature? (The boiler has an 1107-1 control module, if that's of any relevance.) Also, for what it's worth, the actual "feel" of the heating throughout the house has been fine the whole time — i.e., the heat can be felt on all three floors, the radiators are definitely warming up, and the heat itself seems evenly distributed and comfortable.

(3) As regards the pressure values displaying on the gauge during a typical heating cycle, what I've been seeing is that the pressure only rises about by about 2 psi for the whole heating cycle. Is this normal, or should there be wider range of rise?

Any info would be helpful. Thanks.


  • Jamie Hall
    Jamie Hall Member Posts: 18,917
    Pressure rise is great -- shows that your expansion tank is working fine.

    The real question on temperature at the boiler is whether it's the thermostat on the wall which is cutting it off or the aquastat on the boiler. If it's the former, I'd not worry about it. If it's the latter, then does the thermostat also quit later, or does the boiler come back on?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,688
    You're eventually going to need someone to service the boiler. Why not find a hydronics expert now, have them come over the house, explain the system, show you all the components. explain what things you should be doing and how to do them. What to look at for, and when to call. And look for any deficiencies/problems/potential problems.
    And how to add water and bleed radiators.

    Now to answer some specific questions. First a picture of the boiler and it's related nearby piping would help, showing the expansion tank.
    Is your system just one zone?
    Do you also use your boiler to make domestic hot water?

    #3. That's fine
    #2. Not much to do about that. Most likely your boiler is very oversized. Only caveat is if you ever need a boiler replacement, to a proper heat loss, and size the boiler accordingly.
    Although you can adjust the high limit (and low limit if there is a triple aquastat), the boiler will shut off when it either satisfies the call for heat, or hits the high limit. Lowering the high limit will increase short cycling.
    #1. Goes with #2. If the boiler is oversized, it will run less. When you hit the design temperature for your area, the boiler should run continuously. Any other time it will cycle. The farther away from outside design temp, the shorter the cycle.

    A hydronics expert could evaluate your system and maybe recommend an out door reset and boiler protection to eliminate to low of a return water temperature.