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Boiler Water

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ScottMcNab
ScottMcNab Member Posts: 50
Hi
My propane boiler hot water is backing up into the rads backwards through the return lines when no call for heat from thermostat that controls the circ pump. It gets the house warm but the boiler cools down very quickly causing it to fire often and waste fuel. The thermostat never calls for heat as the rads stay hot. The boiler is setup to keep a certain temperature with a high limit and circ pump controlled by thermostat when call for heat. What is the best way to fix this or is it a normal occurrence? What would be a good high limit setting and differential? Thanks

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  • hot_rod
    hot_rod Member Posts: 22,505
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    A pic or drawing of how it is piped would help answer some questions. Often times check valves are needed to reduce "ghost" flow in a system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    Alright. I'll get some pics in the morning for viewing
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    Here are some pics
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    You have a single zone, right? I would add a flow-control valve (lift-check valve) to either the supply or return line.
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    It leaves the boiler in one supply line and splits into 3 and moves around the house and has 2 return lines to the boiler. One line must have a t somewhere. So far it only gravitates backwards into the return lines and not the supply
  • Gilmorrie
    Gilmorrie Member Posts: 185
    edited November 2018
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    OK, that makes it all on one zone, but with branches. Maybe there are manual plug valves for balancing the flow among the branches, but maybe not. If you can prevent the gravity flow in either the one supply or the main return, that will do you. Install a flo-control valve - it will prevent flow except when the pump is running, and then only in the one direction. Done.

    Another approach is to install an electrical zone valve that opens only when there is a call for heat. Take your pick.
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    Perfect thanks. I'll give that a try. How do you prevent the boiler from condensing? If you set the circ pump to come on at 140, it'll circulate all the cool water that's sitting in the rads and bring it to the boiler where it cools down considerably and takes forever to heat it therefore condensing for a while. It's a low mass boiler which holds about 5 gallons.
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    You have a cold-start boiler? Set your aqua-stat to start the pump at, say, 160 deg. Either that, or go to warm-start boiler controls - the boiler is kept always warm, and the extra fuel burned is peanuts.
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    Right now it's set up as a warm start boiler. Aquastat controls the burner so I have it set at 170 with a 30 differential. Home thermostat controls the circ pump. So when house cools and thermostat calls for heat then the pump turns on and hot water is ready to be circulated. Problem now is that the gravity flow is causing the house to heat up well above the thermostat setting. Therefore causing the boiler to cool and run a lot. If I stop the gravity flow I believe the water will stay hot in the boiler as it's not gravitating into the rads and losing heat. Burning through a pile of propane now with the way it's working.
  • ScottMcNab
    ScottMcNab Member Posts: 50
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    Circ pump never turns on as the gravitating water always keeps the house hotter than thermostat setting. With the gravity flow there's no way to control house temperature.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Install a weighted flow check, preferably on the return between the pump and the boiler.

    Or you could get rid of the 3 piece circulator and get a much more efficient wet rotor with a flow check built in. I'm guessing a Taco 0010 or equivalent would be the same high flow/low head characteristics as that B&G you have now.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!