Steam Boiler Sight Glass Q&A #2

How to clean a dirty sight glass on a boiler
Does the boiler have to have a sight glass?
Water level in the sight glass never changes
What is the safe level of water in a boiler sight glass?

Dirty Steam Boiler Sight Glass Cleaning

Sight glass filled with rust and sediment & I'm seeing frequent boiler water additions.

I have an old Burnham water heater [steam boiler] and it has been cleaned less than a month ago.

I have been noticing that the water feeder has been filling water at least 7 times in 24 hours. I am not sure what is going on. I hadn't noticed this until recently.

The water level in the sight glass goes down extremely low until the water feeder fills again to less than 1/2?

the glass is filled with rust and sediment about 1/4 inch high and when i questioned the tech he said it was an old system.

The water heater feeder is UNI-MATCH Universal. Any suggestions. l - On 2018-01-22 by LC -

by (mod)

It's likely that the same sediment and crud that is showing up in your steam boiler's sight glass is also clogging the water level sensor or float or control on your boiler.

You'll need the boiler to be thoroughly cleaned. The boiler is drained, flushed, and probably treated with an appropriate steam boiler chemical.

How do I flush or clean out the boiler sight glass?

On a Weil-Mclain 68 steam boiler about 20 years old, i have always periodically "flushed" a few gallons of dirty water out of the system using blowdown valve (i think that is what it is called -- you can see it attached to black structure (yellow handle) to right of sight glass in picture above.

Now the water barely comes out, so it must be clogged. is this something I can clean out myself? On 2015-12-21 by will wallace

by (mod) - Quick & easy steam boiler sight glass cleanout

Will

Boiler experts like the Hartford Steam Boiler Inspection & Insurance Co., recommend a quick and simple steam boiler sight glass flush procedure to clean it out.

Excerpting from HSB's Boiler Maintenance Log Instructions (cited below)

WATER COLUMN OR GAGE GLASS (Steam Boilers) –

For low pressure steam boilers, flush water column, and gage glass weekly.

Open drain valve quickly to void small quantity of water.*

Water level should return quickly to normal operating level when valve is closed.

* All Discharges must be piped to a safe place.

We continue: If you need to disassemble the sight glass for more-aggressive cleaning such as using a bottle brush or replacing the sight glass, it's best to use the brand and model of your boiler to pick up a copy of the boiler's installation and maintenance manual.

If you don't have your boiler manual find it

at MANUALS & PARTS GUIDES - HVAC - home - Master Index to All Brand Names & HVAC manuals, wiring diagrams, installation and repair guides

It may be something a homeowner could do but there are risks including scalding burns, having to drain down the boiler if the valve can't be isolated by shutoffs, and on old equipment there's a risk that you take the valve apart but can't reassemble it because you need replacement gaskets or o-rings.

So consult the manual and consider asking your heating company to do the job.

The service tech will

1. Turn off heat and let the boiler cool down to a safe temperature for draining and repair
2. Drain the boiler water level to below the bottom of the sight glass lower control
3. Loosen the control valve fittings that secure the sight glass
4. Loosen and as necessary remove the top and bottom control valve assemblies
5. Separate the sight glass control valves from the sight glass itself
6. Use a bottle brush to clean the interior of the sight glass - or replace it with a new sight glass
7. Re-assemble the sight glass assembly onto the boiler and carefully snug up the sight glass fittings at the upper and lower control valves
8. Re fill the steam boiler
9. Turn up the thermostat, call for heat, let the boiler return to full operating temperature and then check for leaks

Details are at

HSB, HEATING BOILER LOG [PDF] (2020) The Hartford Steam Boiler Inspection and Insurance Company Attn: Inspection Services Hartford Steam Boiler PO Box 61509 King of Prussia, PA 19406 USA, Email: NSCINSP_hotline@hsb.com - local copy saved as Steam-boiler-Log-HSB.pdf

SIGHT GLASS REPLACEMENT

and at STEAM HEAT TROUBLE SHOOTING MANUALS

Safe Water Level in the Sight Glass

What is a "safe" water level on the boiler sight glass?

I have two Weil-Mclain boilers. One seems to consume a little more water than the other. In order to compensate for this, and not have the boiler quit, because of low water, I add additional water to the sight glass.

What would be too much water and what is a low lever whereas the boiler will not come on. Thank you On 2017-04-08 by Guy P.

Reply by (mod) -

Good question, Guy. My OPINION (which means I don't know) is that if water is above the "SAFE" level marked on the boiler behind the sight glass but that you can also still see some air in the sight glass above the water you'll be OK.

In our photo of an HB Smith steam boiler shown here my yellow arrow points to the safe water lever line affixed to the boiler face just behind the sight glass. If water is an inch or so above or below that it's OK

but

Watch out: if you don't see water in the sight glass the boiler is unsafe to run and if the sight glass is full of water the boiler is flooded.

Too much water in the boiler will cause malfunction as you'll end up pushing water up the steam riser.

Typically the "safe" water level indicated at the boiler sight glass will be around the middle of the sight glass and in turn, that level is probably in the top 1/3 of the heating boiler's internal water cache.

How low should the water go when the low water shutoff LWCO works ?

How low should the water go when the low water shutoff works
The reading on the sight glass On 2017-04-06 by Tim Murphy

by (mod) re:

Darn good question, Tim.

I think that if water is anywhere BELOW the SAFE LEVEL marked at or behind the sight glass but still visible, that would be a safe LWCO level to shut off the boiler. That would be consistent with the instructions for LWCO's I've read.

The manufacturer marks a "safe" water level right on the boiler.

That is in fact the point at which the LWCO valve should operate.

On some LWCOs such as some McDonnell Miller models there is also a line marked right on the control body too.

Be sure to take a look at your low water cutoff control - LWCO - Or LOW WATER CUTOFF CONTROLS

What happens if we we put too much water in the sight glass?

Our sight glass was empty, so we manually added water (per previous instructions from our HVAC company)only to the correct fill mark. Now the sight glass is overfull, all the way to the top, so the boiler must have added too much water somehow.

How do we drain some water from it, so it gets back to the correct level? What can happen from the sight glass being overfull? On 2015-02-22 by Renee

by (mod) - steam boiler over-full may surge or if flooded, you may not get steam heat out of the system

Ask your heating company about adding an automatic water feeder valve and a low water cutoff valve if you don't already have working versions of those on your steam boiler.

Renee the boiler should have a drain valve. Let the boiler cool to avoid scalding burns and don't force an old stuck drain or you may get into new trouble.

Sometimes crud clogs the sight glass ports and can confuse water levels.

The boiler drain can be used to drain excess water from a boiler but better is to use the flush valve on the low-water cutoff control.

See STEAM BOILER FLOODING / SURGING REPAIR where we explain the causes of water too high in the sight glass or in the steam boiler - and what to do about it.

Is it safe that the boiler sight glass is hot?

The water level sight glass is hot. Is that OK? On 2018-01-06 by John

Reply by (mod) - It's normal but hot water risks a scalding burn

In a steam boiler the water is boiling when the burner is on, and even in a hot water (hydronic) boiler the water temperatures are often well above a scalding temperature, so I offer a two part answer

1. It is normal for the boiler sight glass to be hot from the hot water inside the boiler when the burner has been running
2. Watch out: if the sight glass breaks anyone nearby could be badly burned by scalding water (and of course the boiler would have to be shut down and cooled and the sight glass control knobs closed before the boiler could be refilled and run in an emergency-heat status while waiting for sight glass replacement.

Steam Boiler Sight Glass Water Level Doesn't Change

Sight glass water level doesn't change when I add or remove water in the boiler

Water level on sight glass doesn't move when adding or removing water On 2020-09-21 by Michael Kenny

Reply by (mod) -

Michael

Someone may have left the sight glass valves turned off.

If opening the top and bottom sight glass water valves doesn't fix this problem, the valves feeding the sight glass may be clogged.

To clean those you'll need to cool down the boiler, drop the water level below those fittings, dis-assemble, clean, restore.

Sight glass water level doesn't rise when I fill the boiler, then it over-fills

I have a false reading on the water level in my boiler.

When I fill it up I don't see the water rising in the sight glass, and then the water comes out of the boiler vent [sic - he probably means out of the pressure relief valve!]

Then I have to drain it down to the proper level.

What is the problem?

My friend say he believes it the bottom valve on the site glass is clogged up. Is he right? - On 2018-10-16 by Anthony Ardito

Reply by (mod) - boiler over-filled, relief valve dumps

First be sure that the top and bottom sight glass control valves are fully open.

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

That may require a service call from your heating company to clean the valves and the sight glass itself.

As a residential steam boiler usually runs at less than 1 psi of pressure, if you are over-filling the boiler from the house water supply side, it's easier to push the pressure way over the proper operating level if you overfill the boiler up into the steam piping itself - up above the boiler's top level. Buy t

Watch out: if water is coming out of your boiler's pressure/temperature relief valve then the system is at an unsafe pressure or temperature and you should have it examined by a trained steam heat service technician right away.

No Boiler Sight Gauge?

Can a steam boiler work if there is no water level indicating sight gauge?

Can a boiler work without a water level indicator? On 2017-09-07 by Umar

by (mod) - not in a practical nor safe way

Watch out: The boiler can run without a water level indicator but the danger is that if you cannot monitor the water level the boiler could be damaged, ruined, or even explode if there is no way to check that a safe water level is being maintained.

If you're relying on an automatic water feeder you can't know if it's working properly.

If you're adding water to the steam boiler manually, you have no way to add the proper amount.