Gas Boiler Not Heating Water? A NJ Tech Explains Why | Air Experts

We wish we could tell you there was one simple answer to explain why your boiler isn’t heating your home’s water. But the truth is, there could be a variety of underlying issues here.
Issues that prevent gas boilers from heating your water include:

  • Your boiler isn’t receiving power
  • The gas valve is closed
  • The ignition source isn’t working
  • There’s a water leak
  • The water level in your system is too high or too low
  • The high-temperature limit switch is bad

In this article, we’ll walk through these common boiler problems (starting with the easiest fix) to help you troubleshoot why your boiler isn’t heating your water and what you can do to fix it. 

Potential Issue #1: Your boiler isn’t receiving power

If your boiler won’t even start, the first thing you should check is the power supply. 

If you have a circuit breaker, check your home’s main panel to see if the boiler’s circuit breaker has tripped. If the circuit breaker has tripped, reset it. If your breaker trips again shortly afterward, you should contact a professional to come to take a look. 

If you have a fuse box, check to see if you have a blown fuse. Replacing a fuse can be dangerous, so you’ll want to have a technician come and check for a blown fuse and replace it if necessary. 

Potential Issue #2: The gas valve is closed

If you’ve confirmed that your boiler is receiving power, the next step is to check the gas or propane control valve and ensure that it’s open. If there isn’t any gas making its way to your boiler, your system won’t have the fuel necessary to heat your home’s water.

We know this sounds like an unlikely situation, but it happens! Sometimes when people go on vacation or leave their home for an extended period of time, they’ll close their gas control valve for safety reasons (and forget to turn open it when they return).

If you’ve checked the gas control valve and it’s open, keep reading.  

Potential Issue #3: The ignition source isn’t working

The next step in troubleshooting your boiler is to check the ignition system.

Gas boilers have one of two ignition system types: a standing pilot ignition system or an electronic ignition system. 

If you have an older boiler (20 years +), you likely have a standing pilot ignition system. Older pilot light ignition systems use a pilot light that is lit 24/7 to ignite the main burners. That said, if you have an older boiler and the pilot light is not lit, this is likely the issue that’s preventing your boiler from heating your water.

To relight your pilot light…

  1. Turn the pilot light dial to the OFF position and wait for 5 minutes.
  2. After waiting 5 minutes for the gas to dissipate, turn the switch to Pilot and hold down the reset button. While you are holding the reset button, turn on a long lighter and hold it near the pilot light opening. 

If you have a newer boiler, you likely have an electronic ignition system (hot surface ignition and an intermittent pilot).

To restart your electronic ignition source…

Call a technician. Igniters can be very fragile so we would suggest having a technician check your electronic ignition and repair it if necessary.   

Potential Issue #4: There’s a water leak

If there is any water leaking from your boiler, it likely means that part of your boiler is malfunctioning, and therefore isn’t heating your water properly. 

Boilers can leak from a variety of components, but some of the most common include:

  • Your pipes
  • Pressure valve
  • Pipe fittings
  • Body 
  • Circulator pump

If you find a leak, you should call a technician. He or she will determine whether the leak is coming from and fix it. 

You can learn more about common boiler leaks on our blog, “Why is My Boiler Leaking Water? An NJ Tech Answers” 

Potential Issue #5: The water level in your boiler may be too low or high

The water level in your boiler should stay between 12 and 15 psi (pounds per square inch) of pressure. However, if the pressure inside your system increases beyond 15 psi, your boiler will struggle to work and/or heat your home’s water. 

High boiler pressure can be caused by:

  • Too much water inside the system
  • Parts that are malfunctioning like your pressure relief valve or filling loop
  • Obstructions
  • Buildup of limescale 

If the water level in your boiler is too low, your boiler will undergo something called dry firing, which can cause your boiler to overheat and shut down (thus preventing your water from heating). 

Low boiler pressure can be caused by:

  • Leaks
  • An issue in the expansion vessel
  • Air in your system

If you notice water leaking from your pressure relief valve or see that the pressure on your boiler’s pressure gauge is under 12 psi or over 15 psi, you should contact a trained technician. A professional will be able to add or remove pressure from your boiler safely and correctly. 

Potential Issue #6: The high-temperature limit switch is bad

A high-temperature limit switch is responsible for turning off your boiler if it senses that your system is about to overheat (most high-limit switches kick in around 180-200 degrees Fahrenheit).

However, sometimes, your high-temperature limit switch can go bad, which can allow your boiler to overheat and shut down. 

To reset your limit switch:

  • Make sure the boiler has cooled down.
  • Open the panel on your boiler and push the reset button.

If your boiler doesn’t turn back on after pressing the reset button, it’s possible the high-temperature limit (cutoff) switch is bad. You’ll need an expert to take a look at it for a diagnosis.  

Boiler still not working? Call a certified professional.

Want a water heating expert to take a look at your boiler? Contact Air Experts for quick boiler repairs, maintenance and installations.

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