When troubleshooting a boiler, remember these words of wisdom: The troubleshooting mind is like a parachute. Both must be open to work properly.

Troubleshooting a boiler problem is pretty simple if you follow these tips:

  • Don't assume you know what the problem is before you get started
  • Always troubleshoot systematically
  • Think about the problem and ask questions.

The importance of following these tips is illustrated by the recent experience of Jeff Young, a radiant heating and boiler expert in Easton, PA. It's a story that holds a lesson for every technician who performs service work on boilers.

Young was called in to troubleshoot a finicky propane boiler. Although the boiler would work fine much of the time, it would often lock-out on low gas pressure in the morning and evening. It would lock-out unpredictably at other times, too, but early morning and early evening were most common.

Young was the fourth technician to be called about this boiler. If he couldn't fix it, the next call was going to be to a priest to perform an exorcism.

Young relates that when he arrived on the job site there were five or six gas valves on the floor. Apparently, the other technicians had all arrived at the same conclusion: the gas valves were all bad, so they kept replacing them. Someone needed to open the parachutes of their minds.

Young decided that the likelihood of five or six brand new gas valves being faulty was pretty slim, so he started by applying troubleshooting tip #1: he didn't assume he knew what the problem was. Logic, common sense, and the odds were on his side, too. You simply don't get six straight "bad" gas valves. If the valves were truly junk, there would be dozens, if not hundreds, of boilers everywhere having the exact same problem. If not, then why were the gas-valve gremlins picking on this one poor customer?

He then diagnosed and solved the problem by applying tip #2: systematic troubleshooting.

Systematic troubleshooting is just what it says. It involves solving a problem in a logical, orderly manner by following specific steps.

First, identify the sequence of operation from the very beginning. It's best to start at what we call the "head-slappin' simple" end, because if you don't start there and something very simple turns out to be the problem, you slap yourself in the head for not finding it sooner.

In the above example, Young had two operation sequences to follow: the "call-for-heat" sequence and the "get-propane-to-the-burner" sequence. By applying the "head-slappin' simple" strategy, he decided to eliminate the call-for-heat sequence by running it through its paces. He turned on the thermostat and followed the wires.

Thermostat to relay? Check.

"Hot" side of the relay to zone circulator? Check.

"Dry" side of the relay to the boiler control? Check.

Boiler control to burner control? Check.

Burner control to spark ignition? Check.

Burner control to gas valve? Check.

Nice blue flame? Check.

In a matter of five minutes, Young saved himself a head slap, eliminated 50% of the possibilities, and narrowed his detective work to the "get-propane-to-the-burner" sequence.

In keeping with the head-slappin' method, he started with the simplest explanation possible by checking the propane level at the tank. He then applied a systematic troubleshooting approach by making sure there were no leaks between the tank and the boiler, as well as the home's other propane appliances.

Next, he used his manometer and checked the gas pressure at the boiler to make sure the gas pipe was sized properly. There was plenty of pressure, so that was eliminated.

Plenty of propane, no leaks, and adequate pressure. Young had already done more than any of the previous service techs and still hadn't found the problem. He then applied troubleshooter tip #3: Think about the problem and ask yourself some questions.

The boiler would typically lock-out in the morning and the evening, as well as at other arbitrary times. Why would a boiler behave that way? What would cause the gas pressure to drop at the boiler at certain times of the day? He thought about the fact that the boiler was at the very end of the gas line. Between the tank and the boiler there was a water heater, a dryer, and an oven and stove.

This realization started a line of thinking. What if the water heater was running at the same time as the boiler? That would happen in the morning when the home’s occupants were showering, wouldn't it?

Young fired the boiler and then turned on the hot water. By simply watching the boiler flame, he could see it dim considerably when the water heater burner switched on. Still no lockout, but an important clue.

People sometimes cook in the morning, don't they? He had his partner turn on some of the burners on the stove and watched the boiler flame dim even more.

What if the clothes dryer was also running in the morning? He turned on the dryer, and—bingo—off went the boiler.

It was the perfect storm: a call for heat combined with showers, breakfast and wet clothes. He talked with the homeowners about their routines and found that their teenage children did their own laundry, and usually washed them at night and dried them in the morning before school. At the same time, everyone in the house was showering and making breakfast. The result? The boiler control locked out due to low gas pressure.

That explained why, but it didn't solve the problem. Shouldn't the system be sized to handle that scenario?

Again, tip #3 applies: ask yourself another question.

There was plenty of gas in the tank, the pipe was sized properly, and there were no leaks. But as more appliances fired-up, the gas pressure dropped like a rock. What could cause that?

The only other item in the chain that hadn't been specifically checked was the regulator at the gas tank. As it turned out, the propane company had put the wrong regulator on the tank when it was installed.

Looking back, the answer seems pretty obvious. But mysteries are always like that once they're solved. Apply the troubleshooting tips provided here, and get ready to start solving your own boiler mysteries and providing your customers with the expertise they deserve on service calls.

John Barba is residential training/trade program manager, Taco, Inc. He can be reached at 952/237-5230 or by e-mail at johbar@taco-hvac.com

Beyond troubleshooting: optimize boiler efficiency

Once you have finished troubleshooting a boiler and have it up and running, it's time to optimize its efficiency. The quest for optimum boiler system efficiency has led system designers to examine the relationship between flow rate, Btus, and the system's Delta-T.

The formula to determine the flow rate (in gallons per minute) required to heat a zone is equal to the Btus that the zone requires at a given point in time, divided by the system’s Delta T, times 500. The 500 is a constant that comes from multiplying the weight of one gallon of water times the number of minutes in an hour, times the specific gravity, times the specific heat of the fluid.

Precisely matching water flow with the boiler firing rate dramatically improves system efficiency by preventing system short cycling.

When a boiler is firing and pumps are operating at a fixed rate, a reduction in heat load (caused, for example, by warmer-than-design outdoor temperatures), leads to the system satisfying the call for heat quickly. This leads to short cycling on two levels: the boiler is running for a shorter period of time because it satisfied the zone so quickly, and the water coming back from the zone is warmer, which makes the boiler short cycle even further.

When boilers short cycle, the overall efficiency of the system takes a hit. The burner never gets the opportunity to burn at its peak, steady-state efficiency. It's similar to a car that is always in stop-and-go city driving and never on the highway.

New circulator pump technology that varies the flow based on temperature differential rather than pressure differential is a key to a highly efficient system. If you have a circulator that varies its speed based on the temperature difference of the fluid going out to the radiation and the fluid coming back from the radiation, that Delta-T gives you a precise idea of what’s going on in that system at any given point in time. It tells you exactly how many Btus are required in the zone you're trying to heat.
— John Barba