Do it Yourself: Re: [DIY] High gas boiler CO

27 January 2014

Re: [DIY] High gas boiler CO

I suppose based on what you have written that your orifices are fixed rather than being adjustable. You might try injecting a very small amount of air into one of the burner throats to see if it improves the flame, which would indicate that there is too much gas for the amount of the air being drawn into the burner throat.. I suppose it is possible that the orifices are too large in which case it has in all probability been this way since originally installed. Stack CO emission measurements and limits is a fairly recent requirement and as long as all of the combusted gasses are in fact going up the chimney you would not get any CO back flow into the furnace space. It is doubtful removing two of the burners would have any effect on this problem other than reducing the btu of the boiler which might prove less than advantageous.

Dale in the Flatlands. "Why waste time learning when ignorance is instantaneous."

sparks06524 wrote:

In one of my rental houses is a 1985 vintage Repco gas fired 150K BTU/hr boiler.

I've had both a gas company tech and an independent HVAC guy check it after it was red tagged for high CO in the stack gases (about 238PPM).

The only suggestion made by the first gas tech was a thorough cleaning of the boiler and its burners.

I opened it up, wire brushed the flu passages and the pins (cast iron), blocked off an unused chimney vent to an old water heater, pulled out and cleaned the 6 shotgun burners and then called in another tech.

The stack CO was slightly better but not much. The burner shutters are wide open but the flame tips are still heavy yellow. Reducing air only makes it worse.The manifold gas pressure is normal, input gas pressure is normal and draft is normal based upon instrumentation.

The last tech thought there was some flame impingment based upon the fact that the flame tips were hitting the bottom of the cast iron assembly. He thought that the combustion chamber was too small for the 150K/BTU/HR rating. However, he then said "but I don't know how this was designed". The upshot is that it's been working this way for the 15 years I've owned the house with no detectable CO readings on a digital CO detector in the boiler room. The three techs had no other suggestions.

I've been thinking of pulling one burner from each side (6 burners at 25K each), of course plugging the manifold oriface for each, thereby reducing the boiler input to 100K BTU/HR. Since there is only about 60K BTU of radiation capacity in the house, I might improve efficiency and lessen potential CO.

Any thoughts?

Doug