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Gas Smell on Start of Gas Boiler - Columbia MCB-170J

mawst95 Member Posts: 1
Hi everyone,

We moved into a 1937 home last year. It has a Columbia MCB-170J gas boiler, with radiators throughout the apx. 3000 sq ft of finished space. The boiler is in a room in the basement (probably 15 x 10) with a gas water heater. It is flanked on either side by a room12x15 finished space, and a 8 x 10 laundry room. The rooms are separated by doors with louvers.

When the boiler starts up there is a faint smell of gas. My wife can smell it in the morning most strongly when she gets up. Only smell it in the mechanical room and it quickly disipates.

We've heard conflicting things from plumbers we've had looking at it, our local gas company, and a tech from Columbia my wife called. The gas company person--who my wife spoke with outside of the home when they were doing work on our block said you should never smell gas. The columbia tech and plumber said its normal based on the design. The plumber who seemed to have boiler experience said cold air in the flu in the morning was causing a slight backup of the gases, which then disapates.

Basement in generally is not particularly well sealed I'd imagine given its age. We do have a radon removal system and obviously the dryer in the laundry room, which I guess affects pressure in the area. But the smell isn't confined to when the dryer is running. Sump pump/pit is also in the same room as the boiler and WH. We have a french drain with that mesh stuff on the perimeter near the concrete floor.

After reading the manual for the boiler there is no mention of gas smell being "normal" (in fact just the opposite).

Does anyone have any ideas, questions, or suggested course of actions? Thank you for your help!



  • Jamie Hall
    Jamie Hall Member Posts: 22,175
    A gas smell is NOT normal. The gas company puts an odourant in there for a reason. Nor should you smell combustion products, even first thing. Something is amiss either with the gas train or the draughting, and you need to get someone who doesn't think it's normal but who understands gas burners in there to find and fix the problem.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 14,560
    It's possible the flue is cold occasionally when the boiler starts which hurts the draft. Once the boiler makes a little heat in the flue the chimney starts pulling better.

    Best thing is to get a tech that know what he is doing and have him be there on a COLD start.

    How is the boiler vented? Inside chimney, outside chimney? is the chimney lined?

    It's possible the smell could come from the water heater flue.

    I had one that did that, and it was a dead squirrel in the water heater flue.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,761
    edited January 13
    If I am not mistaken, Radon remediation is accomplished with a fan causing a positive pressure in the home, or at least in the rooms at the foundation. This positive pressure is designed to force Radon away from the interior of the home. If that system is operating properly then it should be less likely that you are having chimney draft problems.

    My guess is that you have a gas leak near the burner combustion air intake that when the gas valve opens, the gas leaks into the room. After the burners fire and cause increased draft in the chimney, the leaking gas gets pulled into the combustion chamber and up the flue. You might want to take a spray bottle with 50% dishwashing liquid and 50% water and spray all the fittings and joints around the burners to find the leak. If you are not comfortable doing that, then ask a professional to do it.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,761
    edited January 13
    Another cause of the gas smell could be that the chimney is down-drafting whenever there is no flame in the boiler. So a perfectly good (non leaking) gas appliance may release gas into the room because the chimney air is pushing the air flow the wrong way. On start up that air mixes with the gas to the burners for a few seconds before ignition and ends up in the room. Once the gas burners ignite, the odor is burnt away with the flame. The byproducts of combustion may or may not enter the boiler room for some time until the chimney warms up and provides the proper draft for the removal of the byproducts of combustion.

    Someone with a draft gauge designed for testing chimneys will be the best professional to find out if the poor draft or down draft condition is causing your odor issue. The gauge is inserted in the vent connector pipe before the appliance is turned on to measure the off-cycle draft. Once that reading is known the burners are ignited and the draft gauge is observed for any change in the chimney draft.

    Only then can you be sure of the chimney situation. Just a simple cigarette smoke near the draft hood smoke direction is not going to give you the numbers. Chimney professionals or HVAC professional or an Oil Heat Technician may have that gauge. Here are the three most popular draft gauges.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    JUGHNE Member Posts: 10,914
    Possibly a test could be done by locking the motorized vent damper open.
    Then warm air from the basement could help warm the chimney to induce more draft thru the boiler

    If this odor happens only in the morning, the water heater may not have fired yet and only its pilot is putting heat up the chimney.
  • Athana
    Athana Member Posts: 98
    edited March 5
    When Boilers (two Steam Smith Series 8) are off because thermostat is not calling for heat for an extended period of time(45 minutes maybe) kind of a cold start we get a noticeable plume of gas off the boilers.We called on the PSEG Worry Free guys and the guy cleaned the spark ignitors of the guns and tightened bolts which were all loose on panel of combustion chambers.
    But now I think I may be smelling it more ??
  • Steamhead
    Steamhead Member Posts: 16,472
    Also, I believe these boilers use slow-opening gas valves. If someone has replaced one with a quick-opening valve, this could be the cause. If the gas valve is a Honeywell, I'm pretty sure the model would be V8204H or V8304H.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service