Steam boiler sight glass questions and answers, set #3.

This article series describes how to find & use the sight glass (or sight gauge) on a steam heating boiler to check or set steam boiler water level.

Steam Boiler Sight Glass Repair Q&A#4

These recently-posted questions & answers about the sight glass on steam boilers appeared originally at SIGHT GLASS, STEAM BOILER - be sure to review the advice given in that article.

On 2019-04-02 by (mod) - steam boiler sight glass can be cleaned

Anna

A steam boiler sight glass can be cleaned by turning off the top and bottom valves at the sight glass itself, then when the boiler is cool AND IF the valves are actually shut and not leaking, the sight glass can be removed and cleaned with a small diameter bottle brush or the like.

To slow the dirt-clogging or obscuring of the steam boiler sight glass, your steam boiler may need to be cleaned - drained of sediment, and depending on water quality, use a chemical treatment.

On 2019-04-02 by Anna

The sight glass gets very dirty and I can’t see the water line. How to prevent?

On 2019-04-02 by (mod) - LWCO leak

Go Bruno, and let us know how the repair works out.

On 2019-04-01 by Anonymous

I have two LWCO valves on the boiler but have a small leak and need to fix......therefore, i needed to know.
thank you,
Bruno

On 2019-04-01 by (mod) -

Yes, Anon, if the valves at the top and bottom of the steam boiler sight glass are closed no water enters the sight glass - the steam boiler will still operate, but you cannot see the water level in the boiler.

Watch out: if your steam boiler does NOT have an automatic water feed valve then you could lose heat by failing to notice that the boiler needs water.

On 2019-03-31 by Anonymous

will the steam boiler work if the sight glass valves are kept shut?

On 2019-03-31 by bruno

will the steam boiler work if the sight valves are shut?

On 2019-02-27 by (mod) - slow leak from the top of your sight glass

Bob

I think you're telling me that there's a slow leak from the top of your sight glass. If that's the case you can turn off the water into the sight glass at the top and bottom and then disassembled the sight glass in order to replace the seal or gasket.

On 2019-02-27 by BOB

QSLOS DRIP From top inside sight glass that moves to top or over top.

On 2019-02-20 by (mod) - When adjusting the water level with the sight glass, what should the valve settings be?

Except for the case when the sight glass is leaking and the valves have to be closed the normal position is open at the top and bottom so that the water level in the boiler can be continuously monitored.

Sometimes the technician may slightly close the bottom and top valves as an effort to deal with surging however that's not the best repair for surging problems in the boiler.

On 2019-02-20 by Chris

When adjusting the water level with the sight glass, what should the valve settings be?
Open on bottom/ open on top, I noticed that the water level doesn't fluctuate when the top is closed.

On 2018-11-26 by Bob Kosiba

Vaporstat set at 1.0 psi, but boiler will not go above 7 oz.
Vaporstat is not turning off the boiler at the 7oz setting.

It is working properly. If I set it at less than 7 oz, it will shut off the
boiler when it should. There has been no water loss in three weeks of operation
so I don't suspect a leak. There is a small drip at one of the radiator
valves intermittently.

On 2018-11-24 by Anonymous - steam boiler normal operating pressure

Bob,

At the risk of being irritating (sorry) I intended to make clear that most residential steam boilers operate at around 0.5 psi. So your system may be operating perfectly normally - check the setting on the vaporstat.

More details are in the reply I posted on Nov. 14 (below).

If I've misunderstood or missed something let me know.

On 2018-11-24 by Bob Kosiba

Vaporstat turns out to be working properly, but pressure will not go above 7 oz. Water level does not go below LWCO. Burner keeps working, but will not increase the pressure above the 7 oz.
No water loss indicated in the sight glass over a three week period.
Any ideas?

On 2018-11-14 by (mod) - normal residential steam boiler pressure levels

Bob:

also see the article dedicated to steam boiler pressure controls at

PRESSURE CONTROL, STEAM BOILERS

and this article on normal steam boiler pressures

STEAM BOILER PRESSURE

On 2018-11-14 by (mod) - Honeywell vaporstat L408J - No matter the setting on the main, the Gauge attached reads .5 psi.

Bob

IF you mean that setting the gauge to a higher or lower pressure is not changing the boiler pressure, even after a heat-on cycle (that would drive the steam vents and thus allow pressure to escape the system)
and

IF the control does not turn off the burner ever,

THEN

yes I agree something's wrong either with the control or with how it's mounted and wired.

In that case let's review the installation details in the IO manual that I give below.

OR otherwise

The control may be working perfectly correctly. It would be quite unusual for a residential steam heating system to want to operate at pressures above 0.5 psi, in fact that's a bit high for many.

Here is what Honeywell says

In all models, the differential is subtractive from the main scale setpoint.

The upper operating point is determined by the main scale setpoint, while the lower operating point is determined by the main scale setting less the differential setting. Operating points are shown in Fig. 7.

Adjust the main scale setpoint for the desired operating pressure by turning the main scale adjusting screw (see Fig. 8) on the top of the case until the main scale setting indicator is at the desired value. Adjust the differential setting by turning the differential adjusting screw until the differential setting indicator is at the desired value.

The scales are marked in psi and kPa.

Consult the operating manual for your steam boiler to confirm the desired or default operating pressure. If you think you need to set pressure higher than 0.5 psi, most likely there is something else wrong with your system such as a condensate return problem.

Below I illustrate this Honeywell L408J1009 control for other readers, and in case you don't have the instructions for your Honeywell vaporstat, you can obtain a copy from Honeywell at any supplier, from Honeywell, or at this link:

Honeywell VAPORSTAT L408J1009 IO MANUAL [PDF] at InspectApedia.com

On 2018-11-08 by Bob Kosiba

Installed a Honeywell vaporstat L408J. Wired across the R and B terminals. No matter the setting on the main, the Gauge I attached reads .5 psi. Switched to a brand new ounce gauge and with 1.5 psi set on the main get 7 oz reading on the gauge. Is this a defective vaporstat or am I missing something?

On 2018-10-16 by (mod) -

I would check to see if the bottom and top connectors that hold the sight glass are debris-clogged.

On 2018-10-16 by Anthony Ardito

I have a false reading on the water level in my boiler when i go to fill it up i dont see the water rising in the site glass and then the water is coming out of the boiler vent then i have to drain it down to proper levels what is tje problem, my friend say he believes it the bottem valve on the site glass is clogged up is he rogjt.

On 2018-10-12 by (mod) - how can the water in the sight glass pulse down from over 3/4 the height

Bob

If the water is actually pulsing then the boiler is surging; that can be due to contaminants in the water; there are also anti-surge additives for steam boilers.

at STEAM BOILER FLOODING / SURGING REPAIR

you will find a discussion of surging problems and solutions.

On 2018-10-12 by Bob Kosiba

I guess my main question is how can the water in the sight glass pulse down from over 3/4 the height
down to LWCO is 2-3 minutes. Is that much water in the boiler being turned to steam in that little time?
If not, what is happening inside the boiler?

On 2018-10-11 by (mod) -

Bob

I don't want to add confusion by guessing further beyond my competence.

But that pulsing down problem acts as if there is an internal blockage in the system somewhere.

When you drained the system did you get a lot of sludge-crud? Could there be more?

Have you been flushing the LWCO as is usually required?

About the old over-fill problem: if you were able to drain the boiler and subsequently delivered steam to the building then any remaining problem would be a subtle one such as having flushed rust and debris into a horizontal section or low section of condensate return piping, causing clogging.

Beware of over-filling the boiler: if you push water out of the top of a steam boiler you can prevent it from sending steam and heat probably won't be delivered as the pressure control will sense over-pressure in the boiler and shut it off.

If there are improperly sloped condensate return pipes that could also aggravate the condensate return problem.
Such as debris clogged pipes.

Also beware of adding a lot of cold water to a hot steam boiler at once - you can crack a section - damaging the boiler or destroying it.

I'd take a look at STEAM BOILER FLOODING / SURGING REPAIR at https://inspectapedia.com/heat/Steam-Boiler-Flooding.php

On 2018-10-11 by Bob Kosiba

No automatic feeder. When I say 3/4 I mean 3/4 of the Height of the sight glass (almost to the top.

I just now filled it to within a 1/2 inch of the top with the boiler off. When turned on, it took maybe 5 minutes to pulse
down to where it cut off.

A minute later it came up above LWCO, proceeded up to 1/2 height, then started pulsing down
again to LWCO, and around we go. I don't believe it was always acting like this.

Some years ago I accidentally left the fill water valve on and filled the system on all three floors. After I drained it and cleaned
up the mess of water on the floors, it seemed to be working OK. Could this have any bearing on my problem?

On 2018-10-11 by (mod) - why does water pulse in the sight glass

Bob

I would not assume the boiler is under-sized;

First I'd find the water fill mark indicator on the boiler or sight glass assembly. I'm not sure what 3/4 means in your question: 3/4 an inch above the sight glass bottom? 3/4 of the sight glass height?

There should be a mark on the boiler and also an indicator in its instructions giving the proper sight glass and boiler water levels.

Next: I'd want to check out the automatic water feeder and LWCO (low water cutoff valve) to be sure that they are working properly.

Next I'd check out the condensate return: you could have a blockage or delay in condensate return

Only if this problem you describe has been the case at every heating cycle since the boiler was first installed new would I be quick to suspect its size as a possible problem.

You will want to review our boiler size discussion at RADIATOR VOLUME & BTUs

We describe using Fernox at BOILER CLEANER CHEMICALS / TREATMENTS

On 2018-10-11 by Bob Kosiba

Used Fernox cleaner, left it in 4 days (cold weather so it got circulated). Drained the the boiler, refilled with Fernox Protector added.

Water level in sight glass set just above 3/4. When boiler is fired up, it pulses down to below LWCU and shuts off fire until the water pulses up
again.

Does this mean the boiler is too small for the house?

Before firing up the boiler this fall, I drained the system, flushed and refilled to 2/3 up on the sight glass. I have a manual feed. I added boiler cleaner (Fornax) through the relief valve pipe, then put the relief valve back properly.

When I turned on the system, the boiler started up OK, but the then the water in the sight glass eventually went down to the cutoff level, shutting off the boiler. Then it returned to a level allwing the boiler to come back on and kept recycling like this.

I had to adjust the water level in the sight glass to higher than 3/4 the way up to keep the level from going down to below the cutoff when the boiler is operating. What happened? I could keep the sight glass level at 1/2 to 2/3 up last year without it going to the cutoff level.
Thanks,
BK

...

Continue reading at SIGHT GLASS, STEAM BOILER - topic home, 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 HEATING SYSTEMS & CONTROLS - home
• WATER FEEDER VALVE, HYDRONIC BOILER
• WATER FEEDER VALVE, STEAM

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