Published: August 13, 2015 - by Ray Wohlfarth

Categories: Commercial Heating

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"So, how many of these have you started over the years? " the contractor inquired. He was asking about the boilers we sold him for this project.

I mentally tried adding all the boilers I sold and started and replied with a sense of confidence, "I think between 300-400 over my career." His question had kind of distracted me. I opened the burner control panel and cursory glanced at the wiring for the burner. It looked professionally installed as all the wires were bent and aligned symmetrically .  That was my first mistake. I assumed the burner was wired correctly and did not verify the wiring terminations. After all, when I asked the lead tech if he needed guidance on the wiring of the burners, he told me , "Kid, I have been installing boilers for twenty years and know what I'm doing. I don't need your help " in a most condescending manner. I hate when someone calls me Kid. His response reminded me  of a story a friend told me about hiring a seasoned salesman. This friend was called to sit in on an job interview for the new salesman and afterwards was asked his opinion of one of the candidates.

"He has over twenty years experience. I think I want to offer him the position. " the sales manager said excitedly to my friend.

"He doesn't have twenty years experience. He has one year's experience, twenty times. He does not seem to learn by his mistakes " my friend responded to the sales manager.

While I am usually very methodical when doing a boiler startup, I overlooked the wiring. I progressed through the preliminary safety checks while the contractor foreman inspected the piping done by his crew. The manual main gas valve was closed but the pilot gas valve was open and I checked the flame safeguard for proper operation. After the safety controls were verified, I opened the manual main gas valve. The burner went through the pre-purge sequence which consists of operating the fan long enough to provide four air changes in the boiler. After the pre-purge, which in this case was 90 seconds, the flame safeguard control energized the transformer. The  7,000 volts from the transformer created a spark  to ignite the pilot flame. In that short minute and a half, the boiler, horizontal flue, and chimney  filled with natural gas. The ignition spark ignited the combustible mixture causing a loud booming  explosion. My ears popped and rang for hours afterwards.  Since I was bent down in front of the burner, the force of the blast went over me but I still felt the percussion in my chest and head. The force of the detonation was strong enough to twist the thick welded steel flue from the boilers to the chimney and also blew the flue completely apart from the adjacent water heater. The access door to the brick chimney that is used for cleaning the smokestack was also knocked off its hinges.  I usually keep my hand on the shutoff switch for the first start of the burner in case something happens. I quickly turned the power off to the burner. I had never had to shut the burner off in my thirty years of boiler startups. In addition, both the foreman and I were covered with dirt, soot and frayed nerves. We looked like those old coal miner pictures from the 1800's. The explosion was so loud, it scared the people inside the building and they ran into the boiler room. I did not notice how the room was filled with dust until the people opened the boiler room door and the visibility was so hazy. The cause of the explosion and one of my nine lives being expended was because their installer that had over "twenty years experience" had inadvertently wired the main gas valves to the line voltage terminal. In other words, the gas valve was open any time the power was on to the burner. I was lucky as the main gas valve had been closed until right before the transformer sparked. After the flues for the boilers and water heaters were replaced and we verified that the chimney, boilers and water heater were still operable and safe, I changed the wiring connections to the correct terminals and verified that all the other wires were properly terminated.  I now check every wire connection for the boiler and burner to assure they are on the correct terminal.

Speaking about wiring terminal connections, a loose wire can drive a service technician crazy. When servicing the burner, always verify that the screws holding the wires in place are snug. It is amazing how many burners are shipped with  loose wiring connections on the wiring terminal. I make sure that I check the tightness of each wire when performing regular service on the boiler as well. The burner blower on a power burner typically operates at 1,700 revolutions per minute or RPMs or higher. This causes vibration which loosens the wiring connections.

I have been called the Obsessive Compulsive or OC Dad by my kids because I have been known to straighten crooked pictures while in public but I am not nearly as bad as the first journeyman I worked for in the trade. When he worked on a piece of equipment, he would align all the screw slots to the same orientation. He would say that the alignment shows that the installer was professional. As I got my confidence, I used to turn one screw perpendicular to the others,  just to tease him.

On another project, I found that the burner had no power. The cause was a loose connection on the main power terminal and the wire melted the connection which could have led to a fire. The enclosed picture shows what happens to a terminal when the wiring connection is loose.

When starting or servicing a boiler, always check the wiring connections for snugness and proper termination. 

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