No Water In Boiler Sight Glass [5 Easy Solutions]

Overheating, LWCO difficulties, pressure problems, leaks in the sight glass, defective valves, and other issues are some of the most common causes of no water in the boiler sight glass.

It is important to understand where the water level in your furnace sight glass should be during regular operation to keep your boiler safe.

Knowing the exact water level may help you fix low water or no water in the boiler sight glass by giving you a direct look into your boiler.

No Water In Boiler Sight Glass [5 Easy Solutions]

In a steam boiler, a no water in boiler sight glass problem occurs when the water level drops below the manufacturer’s recommended minimum safe operating level. Because heat transmission to steam is slower than to boiling water.

The metal heats up. When metal becomes too hot, it loses its mechanical strength. Because of that, the sight glass failed to pour. That causes no water in the boiler sight glass.

This is something that needs an immediate solution and this article is about to do so with the five easiest solutions.

Note: Read how to fix when you find your boiler sight glass full of water.

Tools Needed: A small flat-head screwdriver, a knife, a 19 mm wrench, and either a 17 or 16 mm wrench. A couple of monkey wrenches, the top and bottom fittings, the borosilicate sight glass, and some thermal anti-seize paste. A 24 mm wrench is also needed.

1. Overheat Issue

When the water level in a boiler falls below the lowest permitted water level, or even below the top of the tubes, the tubes overheat, resulting in an empty water state.

In reality, if the water level falls below the primary firing tube, often known as the “Morrison tube,” the steel may collapse. Fortunately, with regular boiler care, this may be prevented.


Low water cutoffs are the simplest approach to avoid empty water (LWCOs). Floating bulbs are used in certain boilers, and if the bulb reaches the cutoff level, which is a few inches above the tubes, the LWCO will shut off the boiler.

With a floating system, it is essential to blow down the device on a frequent basis to avoid overheating, which might save your sight glasses from harm and no water solution.  

2. LWCO Issue

Some LWCOs can start and stop both the feedwater flow and the burner. The Primary LWCO is the name of this gadget.

Typically, these gadgets are quite dependable and perform well. However, like empty water in the sight glass, the following variables might cause breakage. 

Parallel circuits are often used to detect a problem or to test a circuit by bypassing it temporarily.

Mechanical and electrical components are recommended to be replaced on a regular basis by most manufacturers. Otherwise, aging may result in electrical shorts, leaks, and component failure.

The LWCO system must be cleaned as part of proper boiler maintenance. However, poor flushing might cause harm as well.

Boilers may become empty due to steam leaks, faulty steam traps, or procedures that demand a high amount of makeup water. Maintenance is required for the whole system.


LWCO devices must be serviced and parts repaired as directed by the manufacturer. To prevent pollutants from inside of the LWCO, these devices must be cleaned out on a regular basis.

These are low-cost steps that may help to significantly decrease and avoid property damage of sight glass and personal harm.

3. Pressure Issue

Unless you are positive there is no pressure or water in the boiler, double-check that both the blue and red shut-off valves in your water boiler are completely closed.

To fix the sight glass and solve the no water problem, you will need at least two closed valves between your skin and steam at 7 bars of pressure.


Use a 16 or 17-mm wrench to open the fittings. Fact: 16 mm nuts are uncommon; most of the time, this thread size corresponds to a 17 mm nut. Unless otherwise stated, all threads are righty-tightly lefty-loosey.

You will also want to loosen the connection on the line that runs down from the glass. However, be sure there is not any pressure in the line and that it will not be throughout the repair.

Check the intake holes and examine them for wear once you have removed the structure without steam spraying all over the place. Steam and hot water wear away at the metal, thus these safety valves need to be changed when the edge of the holes becomes too thin.

4. Leak In The Sight Glass

Leaks may cause a failure, leaving you with no water in the sight glass. You may have a leak in your sight glass if your boiler has been dropping pressure or producing hissing sounds.

Due to increased usage and frost damage, these difficulties are more likely during the winter months. Identifying the source and location of the leak will help you resolve the problem faster and perhaps save you money in the long run.


Inspect the boiler thoroughly for any sign of water damage, take care not to check pipes while they are hot, and inspect all of the boiler’s fittings.

If there are waterfalls under the boiler or coming from tubing around the boiler, it is best to hire an expert to inspect the leak to avoid causing any more problems by trying to investigate it yourself.

5. Faulty Valves On The Radiators

Water will run down the sections of the radiator and through the underfloor plumbing if the valves on your radiators become damaged, which may be difficult to see.

Once you have determined the regular high and low spots in your boiler’s sight glass, take note of them on the glass or anywhere else on the boiler where you can quickly review them.

When you come to know where the water’s limit is, you will be able to see when you are in trouble.


Radiator valves are typically located on the bottom left or right of the radiator and link the pipes to the radiator.

Tie a piece of tissue around the pipe beneath the radiator valve to see whether it is leaking. After a day or two, check to see whether the tissue is still damp. If this is the case, they may need to be replaced.


What happens if you run a boiler without water?

If you run your boiler without water, the boiler steel will get overheated. As a result, at once, the steel will twist and crackdown where there are the welds.

Do boilers need water?

Yes, a boiler needs enough water because it’s designed in such a way that it needs to get a continuous flow of water to run and heat the house with steam. Otherwise, it will result in overheating and bring catastrophe for you.

Can you turn the water off if you have a boiler?

Yes, you can. In the case of a combination type of boiler that comes with a direct water supply, you can shut it off by turning off its main stop valve. But, when you have a hot water cylinder with an indirect supply, then you need to find out the valve. You will get it on the pipe coming from the water storage cistern and going to the hot water cylinder. You need to shut off this valve.

What controls the water level in a steam boiler?

The feedwater regulator valve which is installed in conjunction with the boiler maintains the water level in a steam boiler.

How do I find a leak in my heating system?

Examine the lower division and all around the boiler visually. A leak around the boiler is the most evident indicator of a boiler leak. Examine the boiler thoroughly for any evidence of water damage. Inspect all of the boiler’s fittings and pipes but never do it while they are hot.


Be careful to not add too much water to the boiler sight glass. Instead of steam, water is pushed out of the header, which may be terrible for the whole steam system and damaging to the environment.

Maintaining proper water levels is a tough balance, but with the correct equipment and regular maintenance, your boiler can operate for a long time.

Leave a comment if you have any other queries. We will be here for you as always with better solutions. 

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

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