Oil and Coal conversion boilers that fire but go out quickly

Mitchell & Bryant Mech.

I have gotten a lot of service calls lately on old oil and coal burners converted to gas. I have one old Sears and Roebuck 25 series. Someone tried to install a WF but could not figure it out because of the LWCO only had two contacts that used 120V to activate the LWCO. I change the LWCO and installed a WF on a 24V system. I was told at Johnstone that the PS could remain even though it was 120V because it was just a switch. I fired up the boiler and the water feed and LWCO worked as soon as I supplied power. The GV had been changed to a Robert Shaw by a previous tech. The pilot lit and stayed lit, but when the Tstat called for heat the burner fired immediately with what seemed like excessive force and then the burner and pilot blew out as if some giant had huffed and puffed. The flame was kind of yellowish with blue only close to the orifices. After the flame blew out the gas continued to spew out of the burner for about ten to fifteen seconds. I need direction. What do I check for next.

Steamhead

Overfired?

I'm not the world's greatest combustion man, but it sounds like the regulator on the gas valve is set too high. See if it's screwed down all the way- we've heard of cases where poorly-educated techs make a habit of this. Clock the meter to make sure the firing rate is correct, and set the air shutters using a digital combustion analyzer.

The 10-15 second time delay was probably the time it took for the thermocouple to shut the gas valve after the flame went out. If this is the case, the unit was doing its job.

Also make sure the chimney and flue passages in the boiler are clean, and you have enough draft to pull the flue gases into the chimney.

If you haven't done so already, get Tim McElwain's gas training manuals. Tim is on vacation now, but if you e-mail him at gastc@cox.net he will send you a catalog when he returns.

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