Low Water Cut Off Keeps Tripping [5 Easy Fixes]

The low water cut off switch is a very important safety mechanism for your boiler. According to the National Board Incident Report, a significant portion of occurrences that result in deaths or injuries are caused by low water levels.

So, in case your low water cut off keeps tripping, you should treat it as a top priority to check out your boiler ASAP.

low water cut off keeps tripping

The causes behind boiler low water cut-off failure are low water condition, oil accumulation, defective low water cut off or LWCO probe, faulty LWCO switch, and bad or incorrect grounding.

Keep reading our low water cut off troubleshooting guide to fix your heater ASAP.

Table Of Contents

Low Water Cut Off Keeps Tripping [5 Easy Solutions]

For a tripped low water cut off manual reset is the first thing you should try. After resetting your boiler, if the same failure code shows up, you need to look deeper.

Most of the time one of the 5 issues that we will discuss in-depth below is responsible. So, without much ado let’s dive into how you can diagnose the underlying cause and fix your heater.

Note: You can also read how to fix the Boiler Pressure relief valve keeps going off.

1. Low Water Condition

When the water level in a boiler falls below the lowest allowable water level or below the roof of the tubes, it creates a low water condition that causes the tubes to overheat.

Low water in the boiler can lead to damage such as loose tubes, fractured tubes, melted metal, and water leaks.


Take a look at the sight glass to see where the water level is. For your reference, check out the figure below to get an idea of what a normal water level looks like.

Fig: Sight Glass Water Levels

Next, check the pressure of your boiler. A pressure of 12-20 PSI is considered normal. So you probably have good water in your boiler pump if both the sight glass water level and boiler pressure are in the normal range. If that’s the case, move on to the next steps. 

If not, you need to add more water to the pump. Before adding water, the system must be turned off and properly cooled. The boiler should be close to the feed water shutdown valves. Offset them and wait.

Find the feed water pipe once the boiler has cooled. This is located off the cold water line that connects to the tank pipe. Gently open the feed water valves.

Pour clean water into the container carefully until it reaches the appropriate level while keeping a close eye on the sight glass. Keep in mind that steam radiators don’t need to be bled.

2. Oil Accumulation

If your boiler has oil added to its water volume, it will accumulate at the top of the water storage and create an unsatisfactory boil. This can cause a lot of issues in your boiler including low water cut off switch tripping. 


To solve this issue you need to thoroughly skim your boiler. Follow the instructions below to skim your boiler water properly.

Step 1: Cut off the boiler’s electrical supply. Before attempting to remove any components, let the boiler cool and the pressure drop to zero. Test the pop safety valve to determine the pressure.

Install the skimmer valve & skimming tubing as described in Figure B while there is no pressure in the boiler. 

Step 2: To assist avoid hot skimming discharge from leaving the bucket and creating a dangerous scenario, make sure the bucket is used to catch the discharge and is covered with a cloth.

Step 3: Open the skimming valve very cautiously; don’t open the boiler’s drain valve. Refill the boiler with water gradually until it begins to leak into the bucket. Keep the water level at this level.

When the boiler is on, let the water slowly skim off the surface and deep into the container. Empty the bucket frequently and keep skimming. Keep repeating until the system and system water are fresh

Step 4: After you’re done, take out the tee beneath the pop safety valve, detach the skimming piping, and install the pop safety valve in accordance with the boiler’s installation manual. Between the boiler and the pop safety valve, no valves should ever be installed. 

Step 5: In accordance with the installation manual for the boiler and local regulations, install discharge pipes on the pop safety valve. A pop safety valve should only be connected to a pipe that is the same size as the pipe attached to the valve.

Never reduce the pipe size that connects to the pop safety’s intake and discharge sides. Never place a valve in the piping leading to or leaving the pop safety valve.

3. Defective LWCO Probe

The LWCO probe is a very sensitive part of your heater. It is what actually determines the water level of your boiler. In case you have a defective temperature probe, it may be why your low water cut off keeps tripping.


You need to test the LWCO probe to see if it is okay. Here are the situations that you need to check for.

  • The LWCO module may be sensing a weak current flowing through the probe if its red light flashes.
  • You can be sure there is a problem with the LWCO probe if the red light on the LWCO module only illuminates when the yellow and green lines to the LWCO probe are jumpered together.
  • Check to see if the probe is corroded. If yes, that means it is damaged.

In case you detect any of the situations above, you need to replace your LWCO probe. Watch this video for help if you don’t know the process.

4. Bad Grounding

Another main reason that can be why your low water cut off keeps tripping is an improperly grounded boiler.


Your boiler needs to be grounded all the way from the electrical panel to the actual boiler. Grounding can be tricky if you don’t know how to ground a gas boiler or what you are doing.

We recommend you get help from a professional to fix this issue for you. Here’s a helpful video for you on this topic if you want to give it a try yourself. 

5. Defective Low Water Cut Off Switch

If you have a defective low water cut-off switch, it can be why it keeps tripping even without any issue with the water level or any of the issues mentioned above. 


Replacing the low water cut off switch is pretty straightforward. Just follow the instructions below. 

  • Unscrew the screws that are holding the switch cover in place. Take off the cover. You will be able to see the board and wiring. Mark all the cables so when we put it back together you will know where to connect all those cables to.
  • Remove the cables after labeling. Now, it’s time to remove the board. You probably will only have to unscrew a couple of screws and pull at the board and it will come right off.
  • You will be left with the probe only. If it appears corroded or defective in any way. It is better to replace this part too. Just loosen the probe by twisting it with a 13-inch wrench or so.
  • Put the new probe in. Then the new switchboard and reconnect all the cables. Cover up the board and screw it tightly. 

Hopefully, at this point, your boiler is running as well as new.

How To Prevent Low Water Cut Off Switch From Tripping

A low water cutoff switch is very important for your heater’s safety as well as yours. However, as great as this safety mechanism is, it can fail too if you are not careful and result in catastrophic accidents.

All you need to do is follow the precautionary steps below and your water level will be good as well as your LWCO switch.

i). Regular Cleaning & Other Maintenance

Every day, blow down the level controls, auxiliary low water cutoff bridle, and LWCO bridle. Solids will be removed thanks to this. Remove silt, this often entails opening and closing a valve repeatedly.

On high-pressure steam boilers, fast drain tests on the LWCOs are frequently performed on a weekly or daily basis to guarantee safe operation. The column and pipes surrounding the switch are cleaned by this blowdown.

The blowdown will either turn off the boiler or cause an alarm or indication light to go off.

Even if the shunt avoids a burner trip, boiler controls with a shunt button should provide verification that the low water switches are functioning. Without a shunt button, it will be necessary to trip the boiler to verify that these low-water switches are operational.

Slow drain tests must be carried out every two years or as instructed by the AHJ, your insurance company, or the boiler manufacturer.

ii). Monitor Mineral Or Sediments Buildup

All low water cut offs are prone to deposit buildup in the float or conductance probe chamber and the bridle piping. The switch used to measure the water level may become inoperable due to this buildup.

This leads to a variety of issues! You can lessen the likelihood of such a mishap by blowing down these wires. At every interior inspection, open the floats, switches, and bridle tubing crosses to check for accumulation.

iii). Perform Low Water Cut Off Tests

By running these tests, we can simulate low water conditions more closely. Here’s how to conduct a slow low cutoff test in the best possible method.

Your burner must be set to 50% or less for the test to work. You’re going to shut off the feedwater pump rather than opening the blowdown valve to compel an immediate low-water scenario.

The boiler will start turning all of the remaining water into steam once the feedwater supply is cut off, which will cause the water level to gradually decrease.

At the sight glass, keep an eye on the water level. The burner ought to turn off when the water level is low. Your system has failed the test if, during this test, the water level drops below the sight glass while the burner is still blazing.


What happens if you don’t put salt in the water softener?

The water won’t be softened without salt, and the control valve will be filled with hard water instead.  That indicates that using hard water will clog your pipes and reduce the effectiveness of your water heater.

Should a water softener be full of water?

For maximum effectiveness, keep your brine tank no lower than four to six inches below the top of the tank and at least one-quarter full of water softener salt at all times. Verify that the salt level is consistently kept a few inches above the water line.

What is a floating ring in a safety valve?

The floating ring is used to enable the exhaust steam piston to move freely. This floating ring can be found in a new style of safety valve. After the prolonged operation, the exhaust steam piston became trapped in the safety valve type that was previously in use.

How much does it cost to change a PRV valve?

Valves for reducing pressure prices start at about $50. It would probably cost you roughly $350 to hire a professional plumber to install a new pressure reduction valve. You can buy one and install it yourself if you’re a more DIY-inclined homeowner.

What is the reset pressure of the safety valve?

The safety valves must be reset at a pressure that is at least 2.5 percent lower than the specified pressure, but not more than 5 percent lower. For valves with a body seat bore smaller than 32 mm and/or a set pressure of 2 bar gauge or less, the 5 percent restriction is increased to 10 percent.


The causes we mentioned above are the most likely reasons why your low water cut off keeps tripping.

However, if you have more questions relating to your boiler’s water cut off switch or just your boiler in general, leave us a comment and we’ll get back to you soon. 

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