Boiler startup dangers
Leave no loose ends.
A wiring terminal block for a commercial gas boiler. Photo credit: Ray Wohlfarth
When the wiring connection is loose, the wire can be burned off, as shown here. Photo credit: Ray Wohlfarth
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 replied with a sense of confidence, “I think between 300 to 400 over my career.” His question had kind of distracted me. I opened the burner control panel and gave a cursory glance 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 condescendingly told me, “Kid, I have been installing boilers for 20 years and know what I’m doing. I don’t need your help.” 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 a job interview for the new salesman and afterward was asked his opinion of one of the candidates.
“He has more than 20 years experience. I think I want to offer him the position,” the sales manager said excitedly to my friend.
“He doesn’t have 20 years experience. He has one year’s experience, 20 times. He does not seem to learn from 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 afterward.
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, used for cleaning the smokestack, also was 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 needed to shut the burner off in my 30 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 1800s. The explosion was so loud, it scared the people inside the building and they ran into the boiler room. I did not notice that the room was filled with dust until the people opened the boiler room door and the visibility was hazy.
Leave no loose ends
The cause of the explosion and one of my nine lives being expended was because their installer who had “more than 20 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 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 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 higher. This causes vibration which loosens the wiring connections.
I have been called the Obsessive Compulsive 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, 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 picture to the left 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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