This client had a complaint that the boiler was working on and off. They stated that the thermostat was set for 72 degrees but never seemed to make it past 62 degrees. They tried bleeding the radiators, but that made no difference. They called me in to take a look and see if I could figure out what was going on. I checked the thermostat and it was operating properly. So, I went down to the boiler and checked the pump and water pressure. Both were within spec. As I was checking the pump, I could hear a constant “ticking” sound from the burner area. I removed the door to find the pilot lit but the sensor not sensing the flame. I also noticed something else, the pilot flame appeared to be very small. I shut the power to the boiler off and removed the pilot. I found a dirty flame sensor, but not too bad. I cleaned it and reinstalled it. While I had the pilot out, I blew through the pilot and was unable to get any air through it at all! 

So, I pulled the pilot tube connection from the pilot off and exposed a completely blocked orifice and even the pilot tubing connector was blocked with carbon soot! (photo shown above) I cleaned it off with a wire brush and I paper clip end. I then blew through the tubing and the pilot to be sure it was clear and reinstalled the pilot and tubing. I restored the power and the boiler fired up perfectly with a nice, big, blue pilot flame. With steam boilers, there are many different reasons that it may stop working. The vast majority of them are maintenance-related. In this article, we are going to tackle several of the most common reasons and what you can do to remedy them.


This may seem like common sense, but I come across this all too often. Check the power switch to the boiler. It looks like a typical light switch and where clients run into trouble is when the switch isn’t located on the boiler itself, (shown in the photo above) but in an alternate location on the wall. This can easily be mistaken for a light switch if you just moved into the home and start flipping switches to turn on lights and unknowingly turned off the power to the boiler. After you eliminated that from the equation, look to the breaker and be sure it is on and not tripped. Next, move on to the transformer and be sure you have 24 volts from the output. Last, check the low voltage fuse (if it has one) and be sure it isn’t blown. (shown in the photo above)


This also may sound like common sense, but I recently had a diagnostic call and couldn’t light the boiler pilot. I checked everything and I just wasn’t getting any gas. So I go over to the water heater and sure enough, it was not working either. I walk around the side of the home and found the gas turned off and locked at the meter! (photo shown above) Not only did this poor guy have to pay to have me come out to diagnose his boiler, but he also had to pay his huge gas bill! oops!

Once you have gone through the steps above and are sure that you have power and gas, move on to the next troubleshooting step, water.


Water is another crucial part of boiler operation. The boiler uses the water to heat and turns into steam. Take a look at the sight glass located on the side of the boiler. (shown above) Take note of the water level and the color. If you can’t see through the glass to tell the level, as in this example, remove it and clean it out and reinstall it. (I go over how to do this in another article) Is the water level low? Is it all the way filled up? Is there any water in it? The water level is critical in boilers. Any of these 3 scenarios will stop the boiler. Flush the boiler and fill the boiler till the sight glass is approximately 1/2 to 3/4 full.


Next, we want to move on to safeties. There are several safeties on any given boiler. Check the flame rollout safety switch. This will be located above the burners. (shown in the photo above) 

The purpose of this safety is to protect the boiler from flames “rolling” out of the front of the boiler. Hence the name “rollout switch”. If it gets too hot, it trips and disconnects 24-volt power to the control. If this is the case for you, then you likely have a clogged heat exchanger. (photo of the seriously clogged boiler heat exchanger shown above) This is a serious issue and will also result in carbon monoxide being introduced into the home. This will need to be cleaned out completely before restarting the boiler.                         


You should next check your spill switch. This will look similar to the rollout switch but be located on the backside of the boiler under the flu hood. This is usually resettable. Push the little red button in the center and reset if tripped. These usually trip due to a clog in the flu or if you have a power damper, it may be stuck closed. If the power damper fails, you can switch this to manual, and open the damper up yourself till the damper switch sends power to the control.


Another common issue is a clogged pigtail. This is located on the side of the boiler next to the sight glass and will have a gauge attached to it and what is called a pressuretrol. (shown in the photo above) You will know that this is the issue by looking at the gauge and if it is reading anything above zero psig, the pigtail will likely be clogged. 

With the power off, remove the two wires from the pressuretrol and remove them from the pigtail. Next, remove the gauge and pigtail from the boiler and flush everything out in a utility sink. (shown in the photos above) After you flush everything out, be sure to use thread sealant or Teflon tape on all the threads before you reinstall.

Control Board

The last thing we will cover in this article is the control board. (shown above)

If you have power to the control board at the 24-volt terminal and the 24-volt ground terminal and the board does not send power to the igniter or gas valve, then the control is likely to fail. If power is sent to the gas valve and it doesn’t open, then the gas valve is failed. If the burners ignite but go out right away, it’s likely a dirty flame sensor. “ticking” noise was also gone! The “ticking” was the sparker electrode repeatedly lighting the pilot because the sensor was not sensing the pilot flame. 

This was causing the boiler to periodically light and sense a flame and other times, not sensing the flame. It was pure chance that the boiler would light at all and cause intermittent no heat. 

Another issue could have been if the burner ground was not connected properly. If you have this issue, check all your connections and grounds. 

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