Steam boiler sight glass repair or replacement FAQs:

Questions & answers on how to replace a leaky or broken sight glass on a steam heating boiler.

This article series describes how to fix a leaky or broken steam boiler sight glass to obtain an accurate reading of the water level in the boiler.

We discuss emergency steps such as simply shutting off water into and out of a leaky sight glass as well as sight glass replacement.

Steam Boiler Sight Glass Repair / Replacement FAQs

These questions & answers about how to replace a broken or leaky steam boiler sight glass were posted originally

at SIGHT GLASS REPLACEMENT - be sure to check out the advice given there.

Below is our index to boiler sight glass questions and answers.

Article Contents

• AIR BUBBLES or DIRT IN THE SIGHT GLASS - causes
• LOW WATER in the SIGHT GLASS - risk boiler damage
• LOW WATER in SIGHT GLASS & BOILER TURNS OFF
• LOW WATER in SIGHT GLASS & BOILER DOES NOT TURN OFF - risk boiler damage
• NO SIGHT GLASS - can a steam boiler boiler work safely?
• NO WATER in the SIGHT GLASS - unsafe boiler operation, risk boiler damage
• SAFE WATER LEVEL in a STEAM BOILER SIGHT GLASS
• SIGHT GLASS CLEANING PROCEDURE
• SIGHT GLASS CONTROL VALVES - knobs at top & bottom of the glass
• SIGHT GLASS LEAK REPAIR
• SIGHT GLASS WATER LEVEL DOESN'T CHANGE
• SIGHT GLASS REPLACEMENT PROCEDURE
• SUDDEN DROP in SIGHT GLASS WATER LEVEL - at start or end of a heating cycle - false water line?
• TOO MUCH WATER in the SIGHT GLASS - boiler is boiler flooded, sight glass water level is too high
• WHY DOES SIGHT GLASS WATER RISE - when we have not added water?

How do I change the gauge glass in a boiler?

Tell me How to change gauge glass in boiler? On 2019-01-24 by Rakesh

Reply by (mod) -

Rakesh

To replace a steam boiler sight glass or boiler gauge glass

The boiler is shut down and cooled

Depending on the specific hardware (show us a photo)

it may be possible to close the top and bottom sight glass valves, then unscrew the glass mounting hardware, replace the glass tube with a new one of the proper height and diameter (and gaskets),

then re-open the vales and restore the boiler to operation.

If there are no working shut-off valves at both top and bottom of the sight glass then you'll need to shut down and cool off the boiler and drain its water level below the bottom sight glass fitting.

Be sure you have the right replacement sight glass for your boiler brand and model- sold by the manufacturer as well as by plumbing and heating suppliers, though a generic sight glass replacement will be fine if it is of the proper dimensions.

Detailed procedures and notes about steam boiler gauge glass or sight glass replacement are

at SIGHT GLASS REPLACEMENT

Do I need a steam boiler sight glass replacement kit with one valve, two valves, or no valves?

Some of the water gauge kits come with fittings (maybe a check valve) instead of the handled valves. Some of the kits only come with one valve at the bottom. When do you need to use two valves vs. one, etc.? On 2015-12-18 by Tisha

by mod) - do you need both upper and lower valves on the sight glass?

If I understand your question it's about shutoff valves at the top and bottom of a steam boiler sight glass.

These valves are important to permit the boiler to remain in operation should the glass itself become broken. In a safe residential location where breakage is not much worry or if there are other shutoff valves between the sight glass and boiler, you might be fine with a kit that didn't include both of them.

The valves also permit change-out or replacement of a broken sight glass without having to drain down the boiler.

 

How do I get water out of the sight glass (for cleaning, repair or boiler maintenance) ?

I have a Utica boiler that you add the water manually.

Because the sight glass was a little dirty, I added more water than I should have.

How can I reduce the water level to the normal level?

Whatever part you tell me to use, please tell me where it is located. Thank you. On 2019-04-09 18:13 by Mary

by (mod) -

Mary

Most heating boilers have a BOILER DRAIN VALVE located usually near the bottom of the boiler. It looks like an outside spigot or faucet.

In my sketch you can see a typical boiler drain at the lower right of the boiler, and I'll attach a photo of a boiler drain further down in my reply.

But

WATCH OUT: the drain valve, having never been touched for some time, may be stuck, corroded, or may leak and be impossible to close again completely when you open it.

What I do as insurance is to have on hand a simple garden hose cap that I can, if necessary, screw over the drain opening to stop leaking until my plumber or heating contractor can repair or replace the leaky valve.

Watch out: also not to try draining a hot boiler - you can get burned.

Let it cool down to room temperature first.

Details of how to drain a heating boiler are

at BOILER DRAIN & FLUSH PROCEDURE

Details are at

Above: a typical boiler drain valve - notice the stains on the floor below and the white crud on the mouth of this valve? It has been leaking.

We can defer replacement of this valve by screwing a good quality hose cap onto the valve mouth - it's the same thread as a garden hose.

by Mary

I appreciate your help VERY MUCH!! I will try what you said and try with caution. Again, I apologize and THANK YOU!!!!

 

Why does water stop rising in the sight glass even though I'm still adding water to the boiler?

I have a problem with sight glass level. A boiler is equipped with manual water adding.

When I add water to the boiler manually in the sight glass water rising to some level and stops despite the fact I've not stopped the water. If I do not stop adding water it will flood the boiler

When I unscrew the valve cartridge from the upper valve on sight glass, water in the glass raising and water spews from that valve. Manually I drain the water to the correct level, then install back vale cartridge.

As soon as I install back cartridge, the water in the glass raising up and fill up the glass. When I remove the cartridge, water level lowering to correct level. Both valves on the glass I cleaned and water from boiler have a clean connection with glass tubing. Can you describe the problem, please? On 2018-10-26 by Andrew Brooklyn NY

Reply by (mod) -

If your steam boiler is a newer, smaller boiler and it's quite hot, the lighter, more bubbly water in the steam boiler may not be able to push water higher in the sight glass.

It's also possible that the upper valve on the sight glass assembly is closed or blocked off with crud and sediment.

 

How do I turn on & start using the sight glass after replacing it on my steam boiler?

What is the right procedure to put the sight glass on line again? On 2017-03-19 by Oscar

Reply by (mod) -

Thanks for the great question. Provided there are shut-off valves at the upper and lower sight glass connections, it should be possible to have closed those valves, removed the old perhaps broken sight Glass, install the new one in the same fittings, and then open the valves again.

A little bit of air in the sight glass will not be relevant to the operation of the system.

Watch out:However if the new sight glass leaks then we need to look carefully at the rubber or other seals in the sight glass mounting fittings, because those may need to be cleaned or replaced.

Our boiler sight glass gets so dirty we can't see the water level.

Sightglass gets brown then cant see level . how do you stop the brown water in the boiler. On 2018-10-08 by John Szostek

Is a clogged steam boiler sight glass likely to cause the boiler not to work properly?

When the sight glass gets completely clogged with dark brown crud that's immobile, does this pose a danger to the furnace system assuming all other features are working?After turning the furnace off, obviously the furnace needs to be drained till the water runs clear and "Steam Clean" or another cleaning chemical needs to be added each year.

But does the clogged sight glass pose a hazard until it can be cleaned or changed?

When I had my old oil furnace replace twelve years ago, I replaced it with a gas -hot-water furnace. The contractor did not tell me that it would get clogged with rust from the returning steam until it happened and I called him. He claimed I could / should replace all of the pipes returning the steam to the furnace.

I did not plan on staying or keeping the home that long and he had already soaked me (it appears underhandedly w/ supposed chimney work which another contractor said was fine and not in need of work etc.) for enough money so I declined.

It has an automatic water fill but he said it should be a certain level so I did the manual feed lever fill thing but it continued to fill after I shut the lever off.

The site glass was overfilled so I called him. He seemed to 'panic' and said it had to be drained and he had to run a chemical through it and charged me $275 back in 2007.

He continued to say it had to be done each year or so. This was only a year or 2 after he installed the new furnace. At some point I called in a plumber who was rec. to me by a professional friend of mine. He looked and said: "this furnace was never inspected by the city"!

The new plumber charged me $10 and showed me how to put bottle chemical called "Steam Clean " in it! (Maybe you can recommend a better one) I realized the original contractor who acted like a nice guy and a friend was a freaking thief and con artist and had ripped me off all along from the beginning!

Now my sight glass is filled with dark brown crud. How do I actually remove it. I read your article on shutting the furnace off, letting the water cool and then remove it but it seems anchored on the top and bottom of the actual sight glass with a brass nut on the top and bottom of said sight glass and I cannot remove it with a wrench when I attempt to I had to stop for fear of breaking the glass.

Should I do it or have PSE & G come in and do it since I have a service contract with them. After reading your article it seems like I should simply buy a new sight glass. Also how do I clean the automatic water feeder or can PSE&G do that.

Also how often should it be done. The installer/contractor never gave the the manufacturer's booklet that all products should have! What a piece of garbage he was/is! On 2018-12-18 by Josh

by (mod) - What to do If you can't see the water level in the steam boiler sight glass:

If you can't see the water level in the steam boiler sight glass:

1. If your boiler uses an automatic water feeder and you are maintaining the water feeder and the low water cutoff valve properly (including regular cleaning/flushing of the LWCO) then your boiler may work perfectly well while you wait for a convenient time to have the sight glass cleaned or replaced.
   
   But
2. Watch out: If your boiler relies on you to manually add water when needed then you have to be able to see the water level to fill the boiler properly, so it's time to replace the sight glass or have the existing one cleaned.
   
   We describe that procedure at SIGHT GLASS REPLACEMENT
   
   Watch out: While a skilled homeowner might replace the sight glass by letting the boiler cool down and then disassembling and cleaning or replacing the glass tube (I use a small bottle brush), if you're not experienced and if you're not prepared to replace O-rings or gaskets if your sight glass starts to leak, then you'd better let the job be done by an experienced steam boiler service technician.

Why is water rising in my steam boiler sight glass? I'm not adding any

Sight glass on steam heat furnace with indirect heater water rising without adding it.

I have a manual feed.

I took off union checked manual feed - it's not leaking. Have you got any ideas indirect heater 4 yrs old - Harold Nobile 3/3/12

Reply: here are reasons water may be rising in your steam boiler

Harold, if your system does NOT have an automatic water feeder and you see water level apparently rising in the boiler anyway some explanations could be:

• Condensate is returning to the system from steam radiators and condensate return piping
• A manual water feed valve is leaking into the boiler
• A combination boiler that includes a tankless coil for making domestic hot water is suffering from a leak out of the tankless coil into the boiler

 

What's the height of the sight glass versus water feeder height on a steam boiler?

I had a fill sight glass replaced by a service technician because it crack. Before that repair, my boiler was automatically feeding water.

After the repair, it seems that I manually have to open the valve. There are three valves that are close together and seem to be connected to the same pipe.

Now I have to turn my boiler on much higher than before to get it warm in the house. - Anon 10/23/12

Steam boiler's sight glass is rusty and every time the boiler comes on the automatic water feeder,feeds water to the boiler filling the sight glass above the required level

I have been reading the other problems on this site. Is there a required height for the auto feeder to be installed in relation to the sight glass ? - Phil J 11/2/12

Reply:

Anon: you want to call your heating service tech to have him/her show you the water feed valve setup and to check the condition of the automatic water feeder. Perhaps the sight glass repair stirred debris that has entered a valve or control. Try flushing things out.

Phil,

There should be a tag, mark or line on the steam boiler face behind or next to the sight glass giving the proper fill level. Filling above the glass would be unusual. Perhaps your automatic water feeder needs cleaning, service, or replacement.

These heating boiler leak diagnostic articles may also help troubleshoot steam boiler sight glass crud or leaks:

• BOILER LEAKS CORROSION STAINS - how to diagnose & evaluate leaks on or in heating boilers
• BOILER LEAKS, HOW TO LOCATE - how to determine that a boiler or hot water system is leaking and how to find hidden leaks

...

...

Continue reading at SIGHT GLASS REPLACEMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Boiler Water Control Articles

• BOILER CLEANER CHEMICALS / TREATMENTS
• BOILER LOW WATER CUTOFF CONTROL LWCO MANUALS
• LOW WATER CUTOFF VALVE, BOILER
• LOW WATER CUTOFF VALVE NOT WORKING
• LOW WATER CUTOFF CONTROL MANUALS
• SIGHT GLASS, STEAM BOILER
• STEAM BOILER FLOODING / SURGING REPAIR
• STEAM BOILERS GENERATORS CONTROLS, PRATT for some interesting history of steam generators & steam turbines.
• STEAM HEATING SYSTEMS & CONTROLS - home
• WATER FEEDER VALVE, HYDRONIC BOILER
• WATER FEEDER VALVE, STEAM

Suggested citation for this web page

STEAM BOILER SIGHT GLASS REPLACEMENT FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to STEAM BOILERS

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