Steam Boiler Sight Glass FAQs #3

Q&A: how to clean, use or fix a steam boiler sight glass
Boiler does not turn off when water level falls
No water visible in the sight glass
Water level in the sight glass is low

Low Water or No Water and the LWCO Fails to Turn Off the Boiler!

There is no water in the sight glass and the boiler does NOT turn OFF

My steam boiler doesn’t cut off when the water level falls to a point where I can not see it the light doesn’t come on on it a manual feed and a cycle guard low water cut off middle CG450 On 2019-02-10 by Stafford

[Photo above provided by Ms. Stafford]

by (mod) - What to do when boiler water drops out of the sight glass and LWCO does not turn off the boiler

Stafford,

What to do when the HydroGard LWCO does not shut off the boiler at low water condition

Watch out: Thank you for asking Stafford, as you've touched on a very important safety feature designed to avoid boiler damage, destruction, or even more-dangerous conditions.

It appears that your CycleGard Low water cutoff LWCO is not working, perhaps needing sensor cleaning or, less likely, replacement of the control.

Reading the instructions for your Hydrolevel CycleGuard LWCO we see that periodic maintenance is needed to keep this LWCO working properly.

In particular, the control's sensor probe has to be removed and cleaned of any scale.

TO have space for a thorough reply to your question I have made a new page where I repeat your question and answer it in more detail,

Please see

LOW WATER CUTOFF VALVE NOT WORKING

and let me know how that works for you and do not hesitate to ask further questions or post other photos of what's going on with your boiler.

No Water in the Steam Boiler Sight Glass

Why is there no water in my sight glass? Boiler runs out of water every other day!

Why does my site tube keep running out of water. The boiler shuts off.

I fill it to the appropriate water level. It needs to be refilled almost every other day. It is a Utica Boiler about 6 years old.

This never happened with my previous boiler which lasted 35 years without any issues. On 2021-01-31 by LU

by (mod) - check the automatic water feed control

It's possible that your automatic water feeder has not been cleaned or flushed properly. Debris in the water feeder float can prevent the feeder from operating.

Watch out: if your steam boiler is truly out of water - no water in the sight glass - turn it OFF immediately - the risk is damage or destruction of the boiler if its burner runs when the boiler is out of water.

Is it normal for the sight glass to look empty

Is it normal for the sight glass to look empty when the boiler is running? Or does it have to have water always while is on or off? On 2018-10-30 by Gloria Vergel

by (mod) - no

No, Gloria.

If the valves at the top and bottom of your sight glass are OPEN then perhaps there is a condensate return clog.

It's a helpful diagnostic to tell me when you're seeing no water: at the start, during, or at the end of a boiler-on cycle.

And is your boiler fed by an automatic water feeder valve or are you feeding it water manually

Watch out: running the steam boiler with no water in the sight glass risks damage to the boiler - and it could be unsafe. Turn it off, let the boiler cool, check the water level again in the sight glass.

If water reappears then we may have a problem of clogged, slow condensate return to the boiler.

Ask your heating service tech to explain how water is added to your boiler: is it by an automatic water feeder or do you have to do it manually, possibly daily?

Why do I have to open valves to get water into the sight glass

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 sought glass ? - Phil J 11/2/12

Reply:

Usually on a residential steam boiler, a small valve at the top and bottom of the sight glass are both kept open so that boiler water can enter the sight glass and thus so that we can see the water level in the boiler.

If water isn't being maintained at the boiler water level indicator line you should find on the boiler face right at the sight glass, then if your system uses an automatic water feeder, that control needs repair.

If your steam boiler requires that you add water manually, you'll need to check the boiler water level daily until you have an idea of the rate at which it's using water (of course that varies depending on the building's heating load).

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.

Steam Boiler Sight Glass Leaks, Breaks, Repair

Please see STEAM BOILER SIGHT GLASS REPLACEMENT for steps in repairing or replacing a leaky or broken steam boiler sight gauge or sight glass.

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

Low Water in the Sight Glass FAQs

Why do I have to add boiler water manually if my water feeder has run?

I fill my boiler sight glass, because its low & LWCO has kicked in

But 6 to 8 hrs later sight glass is dry again & the LWCO has kicked in. Why am I having to manually add water to the boiler? On 2017-12-31 by Scott Wilkinson

by (mod) - You should not be filling the sight glass

Scott

Watch out: You should not be filling the sight glass to the top on a steam boiler;

There should be is a mark on the boiler or on the glass telling you the proper water level, typically about mid-glass height. DO NOT overfill the boiler. Doing so can damage the system or cause you to lose heat.

But if the sight glass is empty and the LWCO is not working you'll have to use manual re-fill until you can get a service tech out there to fix the LWCO.

You flushed the LWCO, right?

To be clear, the LWCO is a safety device that turns ON the automatic water feeder valve if one is installed and that turns the boiler OFF if the water level gets dangerously low.

See STEAM BOILER LEAK DAMAGE

Boiler water level drops and boiler will not start

My boiler is new sight glass is a third full and the lower light comes on and the boiler will not start until I add a little water to it.

Then it runs and heats the house.

But the water drops to the bottom third of the sight glass and the light comes on and I have add more water. On 2019-01-03 by Clarence

Reply by (mod) -

That sounds to me as if your automatic water feeder is not working or you have a problem with condensate return delay or both.

I added water to the boiler but there's no water in the sight glass

Also, is it normal for the boiler to take time for the water to settle and show up in the sight glass when it's off? When its running and I add water it shows up in the sight glass quickly. Thanks again.

I have an old Sears Roebuck steam boiler with cast iron radiators. I have had it regularly serviced, have replaced a part, and had other work done on it, and it works well.

It has been off for a year. When I went down to look at it about a month ago, the sight glass was empty so I turned on the valve and added water, watching the sight glass.

After about 20 or so minutes, no water had appeared in the sight glass.

I turned off the water. The next day I added more water -- maybe another 10 minutes or so of slow running water. Again, nothing in the sight glass.

I had to go away for a month and I left the electric heat on to keep the pipes from freezing while I was away. When I returned two days ago, I checked on the boiler and saw that the sight glass is nearly full -- only about an inch of space between the top of the glass and the top of the water level.

There's a mark made with a red marker years ago that says water level in someone's scribble. It is about 3/4 of the way up the sight glass. The amount of water in the sight glass is about 3 -4 inches above that hand drawn red mark. I let some water out into the sump area (I hooked up a hose to the bottom valve)

-- I let out maybe 2 gallons just now -- and the sight glass level has not changed.

My question is this -- is it safe to turn on the boiler or is that too much water? The boiler adds water on its on -- when it is on -- but I also check it every few days and occasionally add water as needed. Any advice would be very much appreciated. Thank you. On 2018-12-29 by Melynda - S

by (mod) - is it normal for the boiler to take time for the water to settle and show up in the sight glass when it's off?

Melynda

I'd sure like to see some photos (use the Add Image button, one per comment) to see the Sears steam boiler and each of its controls including the sight glass.

I don't have enough info to be sure but from your description

First: check that the valves at the top and bottom of the sight glass are open to allow boiler water into that indicator. If they were closed it might be because the sight glass was leaking and needs repair.

Next: it's possible that

1. you added needed water to the steam boiler - up to the fill line

2. the boiler ran, got up steam, sent steam upstairs, lowering the water level in the boiler

3. condensate had not fully drained back to the boiler when you looked again.

4. You added water SLOWLY - which is smart to avoid cracking a hot boiler with cold incoming water

5. You left town and left the boiler off

6. Condensate from upstairs finally found its way back to the boiler - raising the water level so high that we figure you added water too soon or more than was needed previously.

Or There could be a clog in the condensate return line that is slowing water return to the boiler.

by Melynda

Thanks . I'll take some photos tomorrow and attach them. But some more info: The boiler has not been turned on for since late January, 2018. In early January, I had to replace the lower water cutoff and I used the boiler for about 3 weeks after that.

It worked very well. It has sat unused since then. I went down to check on it around Nov 15 when it turned unusually cold here.

I saw that the sight glass was empty and I turned on the valve and added water -- slowly -- even though the furnace was cold. Nothing showed up in the sight glass and I ran out of time to watch it.

The next day when I had time I added more water and still nothing showed up. Therefore, I was afraid to turn on the boiler and instead relied upon the heat pump for heat for the next few days before I left the house for a month.

It is possible, then, that the water in the sight glass showed up shortly after I stopped looking at it. Before I left the house for the month, I turned off the circuit breaker for the boiler (at the same time I turned off the one for the hot water heater).

I returned here late yesterday and did not look at the boiler's sight glass but did flip its circuit breaker back on (when I turned the one for the hot water heater).

This morning, Dec 29, wanting to be able to use the boiler for heat (I vastly prefer it to the heat pump), I looked at the sight glass and was surprised to see water in it.

As I said, maybe the water has been in there since mid-November -- hours after I stopped trying to fill it. I realize how confusing this must seem.

Steam Boiler Sight Glass Water Level Too High, Boiler Flooded

What causes high water level readings in the sight glass.

What causes high water level readings in the steam boiler sight glass. On 2017-04-23 by Anonymous

by (mod)

Typical causes of too much water in a steam boiler are

• Delayed return of condensate (clogged condensate return lines) so the automatic water feeder adds water at the end of a heat-on cycle and then as condensate returns later-on the boiler is over-filled
• Debris or sediment clogging of the boiler's LWCO or water level detection control
• Improperly-adjusted automatic water feeder control
• Manually over-filling the boiler
• A leak from another source into the boiler, such as a leaky water feeder or shutoff valve or a leaky tankless coil

Please see my detailed reply now found at

STEAM BOILER FLOODING / SURGING REPAIR

Why does water keep going up in the sight glass after I remove water from the boiler?

I have an old furnace with water site glass no automatic fill. What to do if the water level in the site glass keeps filling even after bringing down the water level to the proper level? On 2020-06-29 by Doug

by (mod) - Check for improper water feed OR delayed condensate return

Doug

There are a couple of things to check. Let's start with some diagnosis. I

f you turned off the water supply into the boiler and if you're confident that that valve itself is not leaking, and if you then see the water level rise in the sight glass, it is possible that you are seeing the delayed return of condensate to the boiler.

The other possibility is that your boiler has a tankless coil for domestic hot water and that that coil itself has a leak that is sending house water into the steam boiler.

If the boiler sight glass water is at the top of the gauge, do I let water out?

Our boiler sight glass is full.

How do I let water out? On 2017-01-02 by Marty

by (mod) if this is a steam boiler, it's too full

Marty,

Your steam boiler will almost certainly have a low water cutoff valve that is designed to be flushed frequently, usually weekly, for safety.

That will remove water. But if your boiler is over-filling and IF there is an automatic water feed valve installed, that valve may need adjustment or repair.

I drained and refilled our steam boiler to the water line but when I checked later the boiler was too full

So I just drained our system because it was acting funny, spitting water out of the valves, creating a mess in our dining room. Then I manually refilled the system (we don't have an auto-refiller) until the water level in the glass was perfect.

When I went down to check it again after an hour, the glass was over full (couldn't see the line at all). So I drained some water out of the system (it was dark brown and gross).. only to have the low water shutoff light go on. How can that be? I still can't see the water line, even though I do see a tiny bit of sediment floating in the glass, so isn't it OVER full? On 2016-12-21 by Sue

by (mod) re: draining water at the boiler won't fix spitting steam vents; delayed condensate return ?

Sue

Draining a boiler would not fix a "spitting valve" in an upstairs floor. More likely you were seeing steam or water leaking out of a steam or hot water radiator at a valve or vent.

Your description sounds as if no one has been flushing the low water cutoff LWCO valve.

Take a look at the maintenance instructions for yours. Typically it's a weekly-task to prevent valve clogging - that can be unsafe.

Also, IF your steam heating system's condensate return piping is clogged or partly clogged, or steam traps at radiators are clogged with rust and crud, then the return of condensate to the boiler could be slowed. In that case, filling the boiler while there's condensate still in upstairs piping means that later as that condensate returns the boiler is over filled.

And you are also right to question the automatic water feeder. If it's not working properly it too could be the culprit.

Boiler sight glass was overfull, LWCO shut down the system ?

I'm sorry, I wasn't clear. The water in the glass was over-full, and a spitting stream of water was coming out of 2 of our upstairs radiators. Around the same time, the pressure valve popped on the boiler and the boiler room filled with steam.. so I turned everything off and drained the system until nothing else would come out.

Then I refilled the system to the line. True, I probably didn't wait for the water to drain back into the system from the radiators.

That could've accounted for it being overfull. But that doesn't explain why an hour later the LWCO valve turned on and shut down the system. I couldn't even see the level in the sight glass, so it was definitely too high! So I drained it all again, and the water was just as sludgy this time as the last.

I think there's a ton of sediment in the system (upon refilling, globs of brown water swished up into the glass). Is there a way to remove the drain/ spigot thingee so I can clear it out?

I've removed the glass before but it's higher than where the sludge has probably settled in the boiler. I'm terrified of breaking it off (and then being without heat in the 20 degree weather we've been having here.) Is there some kind of glue on the threads? It looks gunky and white. If there's another article I could read that could help, that would be great. On 2016-12-21 by Sue

by (mod) re:

I don't think that removing the sight glass is a good plan nor is it necessary. That's not the place from which to drain sludge and debris from the boiler. I would use the LWCO valve drain and flush until the water runs clean. You may need to do that several times.

I'm unclear about why the relief valve opened. That would represent a different and unsafe condition of over pressure or over-temperature in the boiler.

Automatic water feeder is filling the sight glass right up, what do I do?

Sight Glass tube fills with water from automatic feeder.

What do i do to stop feeder from putting to much water into boiler? On 2016-11-06 8 by Glenn

by (mod) - sight glass shows too much water in boiler

Glenn, your automatic water feeder needs to be cleaned and perhaps repaired to avoid over-filling the boiler.

Temporarily in an emergency to keep heat working one can on most steam boilers, turn off the water supply into the automatic water feeder and manually feed water into the boiler using a bypass piping loop that passes around the automatic water feeder - IF your boiler has that feature.

Take care to avoid shocking and cracking the boiler by sending in too much too cold water too fast.

Watch out: For safety it'd be best to have a trained professional repair or replace the water feeder asap.

see STEAM BOILER FLOODING / SURGING REPAIR

Water level in the sight glass is above the index marker. Boiler is over-filling, what do I do?

Sorry. Let me rephrase. The water level in the sight glass is above the index marker. Is there a way to regulate the water level so the water level can go back down. I am getting more water pushing through the system then before.

The sight glass on the boiler is above the water index line. Is there a way to regulate this. I believe my boiler is over filling On 2016-08-01 by David

Reply by (mod) -

David:

If your boiler has an automatic water feeder it or its control needs cleaning and adjustment or the activating LWCO (Low Water Cut Off) control needs to be flushed or repaired.

If your boiler is fed manually, someone over fed it, or perhaps it was fed water before condensate from floors above had returned to the boiler.

If the water level is still visible in the sight glass and only slightly above the indicator line on the boiler, say an inch or less, cleaning and water feeder may still need adjustment but it doesn't sound like the water level is dangerously high;

If the top of the water column is higher or is out of sight entirely then you should call for service and repair; that will involve both draining some water from the boiler and fixing its water feeder.

Water in the boiler sight glass goes past the indicator, almost to the top of the glass. Why?

The water level in site glass exceeds the level almost to the top of the site glass and then furnace turns off.

Where is this water coming from

The furnace should work in the reverse as furnace is putting put hear the water should drop in the site glass.

What is the problem when site glass fills up with water During heating. The water must be drain from the furnace everyday to below indicator level. On 2018-12-26 by Edward K. Parker

Reply by (mod) -

Kevin

When the sight glass shows water filling the boiler well above the recommended fill-level the steam boiler is flooding.

The result ultimately will be loss of heat - and there is risk of boiler damage as well.

The underling cause is usually a problem with the automatic water feeder valve (or someone over-filling manually)

or

sometimes a problem with delayed return of condensate to the boiler from the radiators.

See STEAM BOILER FLOODING / SURGING REPAIR

for detailed diagnostic and repair suggestions.