Risk of cracking gas hot water boiler when adding fresh water

steam_nutmegger

I have a new gas fired Burnham boiler for a hot water heat system. Installed two months ago. Model X2. A week after installation (the first week was warm so rarely heat on), I noticed a puddle in basement under a heat pipe drain spigot that was dripping. I tightened the spigot and that stopped. I should mention that this is a vacant rental I check weekly. The heat ran fine for five weeks. Today I went in (after a few much colder days) and the boiler was racing like it was going full tilt. I lowered the thermostat to see if it would stop (because I thought it might be faulty not turning off). When the boiler stopped running, I checked the pressure gauge and it was almost zero. I keep the water main off as a precaution. I turned on the water and there was a massive whooshing and thumping noise. I have steam in my own house so I thought after opening the main I could add water gradually. I turned off the main and the pressure was about 16. I raised the thermostat and it ran normally. I went back a few hours later and there was not water leaking and it was warm. I raised thermostat and it ran fine. Is there any risk I damaged my brand new boiler? With my steam I always let it cool two hours to condense and then check gauge glass and add slowly if need be.  If pressure is again low next time I check, does that mean a leak somewhere? Should you ever need to add to a hot water heat system? Thank you for any input!

 

hot_rod

does it have a autofill valve? Leave it open for a few days to add water as any air vents out

After that shut iff the fill  if pressure drops again you may  have another leak 

EBEBRATT-Ed

If you have any air in the system the pressure may act funny.

Once the air is out (maybe the installer did not bleed it good enough) you should be able to fill it to 15psi and shut the valve off at the boiler.

Then shut the valve off at the main if you want the water off and open a faucet somewhere to relieve the pressure between the main shut off and the boiler.

Once your sure the air is out the boiler pressure should vary between 15-25 psi depending on the boiler temp. If it does not you could have a bad expansion tank.

If the boiler is hot check the temp first before adding water. If it only needs a little just add it slowly.

WMno57

steam_nutmegger said:

If pressure is again low next time I check, does that mean a leak somewhere? Should you ever need to add to a hot water heat system?

Rarely. On existing systems there may be small leaks at the radiator bleeders. Small leaks between radiator sections that go up the chimney. If you see white or green efflorescence around valves, that's a small leak. On a new system, as @EBEBRATT-Ed mentioned, it may have not been completely bled.
Does the rental have internet? Maybe you could leave a hotspot cellphone and wifi camera there to monitor the pressure gauge?

steam_nutmegger

Thanks for the replies. Some more info. The house is

one hundred years old. The heating pipes have green

at almost every joint. That is why I want the water off

so if it leaks, only the water in the heat system comes

out. There is no Internet. But i should get it in Jan so

I can have some Axis cams in basement to zoom in

on the pressure gauge and thermometer.  The system

has a fill valve. As told to me by installer, when the

pressure drops below a certain point, the valve opens

letting in water. Right now the pressure is around 17.

I have no way of checking the boiler temp or able to

add water slowly. If I need to add, does lowering the

thermostat to shut if off and then waiting how long?

Half hour, hour, two hours? I wait two hours on my

own steam boiler but that is just to condense so i

have an accurate glass gauge level. 

I spoke to the installer only after I added water and 

he told me not to worry as the cold water goes into 

the heat piping and not right into the hot boiler. Does

that sound right?

Why was the boiler racing and shuddering and pouring

out steam through the chimney? Is that a sign that it was

close to the low water cutoff point? Even if I did not crack

it, is that a bad thermal stress to add water to a hot boiler?

Once pressure drops, wouldn't that valve just suddenly

open and add cold water anyway? Though I guess the

boiler water level would not be as low as it might've been.

It runs moderately now and just wafts steam exhaust.

EdTheHeaterMan

Steam coming out a chimney on a water boiler is not a good sign.

Why was the boiler racing and shuddering and pouring
out steam through the chimney?

How do you know it was steam, and not just flue gas condensation? Water is a byproduct of combustion because the combustion air has oxygen in it, and the fuel has hydrogen in it (It's a Hydrocarbon) and hydrogen combined with oxygen just right can make water. Just sayin'

You have an interesting situation, where there are signs of multiple leaking fittings, you only visit once a week, and you have the potential for expensive repairs if something happens because you leave the water on, or if you leave the water off.

HeatingHelp.com is good, but we are not that good to be able to prevent a disaster in a vacant building. Perhaps you can make a special Christmas visit to make sure your investment is safe with multiple visits this week with the water left on for a day or two while the automatic feed does its job of maintaining pressure while the air vents do their job of eliminating air is the system. If properly designed and installed, that will only take about 48 hours of operating time during this cold weather.

Then go back and shut the water main off to see what happens next week. In vacation home towns (where I did lots of work) there were services that checked your vacant vacation home once a week during the winter season, but would check daily when the weather was below freezing. Only seemed reasonable to check daily when below freezing, don't you think? Are there any friendly neighbors by the vacant home that you could trust to check that the heat is on daily during the freezing months?

EDIT: I just thought of something I said about being properly installed. Can you take some photos of the new boiler with the near boiler piping, from floor to ceiling from at least 2 different angles so we can critique the install to see if the air will vent properly or if it is designed like the old school plumbers did in the 1960s and 70s that create air problems. We still have installers that dont understand how to install boiler properly or how to read manufacturers instructions

Zman

These can be a compromise between leaving the water on or off. https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon

It sounds like you may have added cold water to a dry and hot boiler and it flashed to steam. This may have damaged the boiler.

Does you boiler have a LWCO (low water cutoff). If not, it really should!

steam_nutmegger

Thank you for the suggestions. Hope everyone had a Merry Christmas. I have not been back to the house but temps have been above freezing since. I attach some photos from the day of installation. The chimney gas I saw coming out may have been flue gas condensate as temp was 21F and I had not yet added more cold water. But it was streaming out in huge volume and intensity. After adding more water, it was just wafting out as usual when running. The boiler does indeed have a LWCO so (if working properly) the boiler could not have been exceedingly low. From the photos, does new cold water from the main feed into the heat piping and not straight into the boiler? I like the idea of the Pressure Pal reservoir. Is there anything bad about having an even larger size like 17 gallons? Yes, I need to find ways to have someone go in daily when below freezing plus get Internet so I can have some basement zoom cameras that I can access from anywhere, anytime. Thank you!

steam_nutmegger

Photos

hot_rod

nice to see large piping to the indirect

Doug_7

Hi Steam_nutmegger -

Virtually no risk of cracking the boiler by adding cold water to the system to increase the system pressure.

Follow the cold water addition piping - the additional water flow goes straight into the expansion tank to compress the air and increase the system pressure. The boiler loop is full of water - an incompressible fluid. The expansion tank absorbs all of the added make-up water.

Once all the air is gone from your boiler loop, you should have a stable system pressure that does not change much week-to-week.

You could add a simple Low-Pressure switch to the boiler-water system and connect it to a Voice-Dialer programmed to phone you if the pressure drops below a set pressure. Need a phone line.

hot_rod

Doug_7 said:

Hi Steam_nutmegger -

Virtually no risk of cracking the boiler by adding cold water to the system to increase the system pressure.

Follow the cold water addition piping - the additional water flow goes straight into the expansion tank to compress the air and increase the system pressure. The boiler loop is full of water - an incompressible fluid. The expansion tank absorbs all of the added make-up water.

Once all the air is gone from your boiler loop, you should have a stable system pressure that does not change much week-to-week.

You could add a simple Low-Pressure switch to the boiler-water system and connect it to a Voice-Dialer programmed to phone you if the pressure drops below a set pressure. Need a phone line.

Additional water added to the system would only go into the expansion tank if the tank pre-charge pressure was lower than the pressure you are adding.

If static pressure in the boiler is 5 psi, the tank pre-charge at 12 psi, water will not go into the tank until static pressure, at the tank connection, rises above 15 psi.


If the system didn't have an expansion tank, or it was valved off and you hooked a 60 psi garden hose to a boiler with 30 psi, what happens?

Doug_7

If the static pressure in the boiler is 5 psi, and the expansion tank pre-charge is at 12 psi, that means there is zero water in the expansion tank. In this situation, the expansion tank can't do its job. Boiler pressure will be very erratic.

If the boiler loop is already full of water and the static pressure in the boiler is 5 psi, the first ounce of water you add will jump the boiler pressure to 12 psi. The second ounce of water and all additional water will then flow to the expansion tank - no where else to go. The water you add to the system can't go to the boiler, because the boiler is already full of water and water is incompressible.

You should not let the boiler pressure drop below the expansion tank pre-charge pressure. If you want to run the boiler pressure at 12 psi then you should drop the expansion tank pre-charge pressure to something lower like 9 psi so the expansion tank has room to work.

If the system didn't have an expansion tank, or it was valved off and you hooked a 60 psi garden hose to a boiler with 30 psi, the boiler pressure will immediately try to jump to 60 psi - and blow the safety relief valve. The boiler is already full of water and water is incompressible. Why we have expansion tanks.

Try to visualize the water level in the expansion tank. If the expansion tank pre-charge is at 12 psi, then the expansion tank is empty of all water at a boiler pressure of 12 psi, and the expansion tank is half full of water at at a boiler pressure of 24 psi. You are a happy camper with a boiler pressure of 15 - 18 psi.

Best operating pressure depends of course on the height of your system.

hot_rod

You suggested

Follow the cold water addition piping - the additional water flow goes straight into the expansion tank to compress the air and increase the system pressure. The boiler loop is full of water - an incompressible fluid. The expansion tank absorbs all of the added make-up water.



Let say the tank is pre-charged to 12 psi, boiler static is 5 psi. You turn on a fill valve set to 12 psi. Water will go into the boiler, not the tank as the tank is at 12 psi. So the boiler system pressure needs to go up 8 psi before it matches the tank pre-charge.

I'm adding additional water to the system, which shows up as a pressure increase.

If you increase fill pressure at the fill valve to 12.5 psi, water can then enter the expansion tank that is pre-charged to 12 psi.

You should not let the boiler pressure drop below the expansion tank pre-charge pressure. If you want to run the boiler pressure at 12 psi then you should drop the expansion tank pre-charge pressure to something lower like 9 psi so the expansion tank has room to work.. ???

The expansion tank is in the system to accept the pressure increase as the water is heated, and expands. It doesn't have a job, work, to do until the heated expanded water rises above it pre-charge pressure. With few exceptions the pre-charge should match the fill valve pressure.
If the tank pre-charge is lower, you are reducing the capacity of the expansion tank by allowing fill water into it.
Chilled water expansion, and solar thermal tanks are some times set at lower pre-charge to allow a "safety seal" of fluid into the tank as pressure will drop as the water gets cooled. The tank needs to be sized accordingly however.

Depending on system volume, temperature increase, and tank size it may be just a few psi, or it could raise 10, 15 or more psi. The Net Expansion Tables in Amtrol Engineering book give you the factors. I believe the Amtrol tables use 27 psi as the max. pressure for these calculations.

i.e. fill water at 55° to final temperature of 180 the factor is.02738.

So 50 gallons X .02738= 1.369 gallons the tank needs to accept, for the system to stay below 27 psi.

Doug_7

I would not run a boiler at a static pressure of 5 psi with the expansion tank pre-charged to 12 psi because it is not a stable condition.

Sure the expansion tank will protect against increases in boiler pressure due to thermal expansion, but this is not a stable operating pressure situation - pressures will fluctuate greatly and you risk pulling in air through any higher air vents.

If the boiler system is liquid full (no air) like it should be, and you add some make-up water, there is no place for the make-up water to go other than to the expansion tank. Water is incompressible so a tiny amount of added water increases the system pressure very fast to the recharge pressure.

Only if the boiler system is NOT liquid full (i.e. contains tramp air) like it should NOT be, is there any place for the make-up water to go other than to the expansion tank. Air is compressible.

Only if the boiler system is not liquid full (i.e. contains tramp air) would there be any risk of cold mak-up water hitting the boiler - which was the original concern.

For a stable operation the boiler system should be liquid full (no air), and the boiler pressure should be at or a little bit above the expansion tank recharge pressure.

It is OK for the expansion tank to operate with a small amount of boiler system water in it. This gives the most stable operating pressure. It is when the expansion tank goes empty that pressures go squirrelly.

hot_rod

My understanding is the only job of the hydronic expansion tank tank is to accept the volume of expanded water, period.

Where the installer connects the tank into a closed loop system establishes the PONPC.

A mis-applied expansion tank can cause pressure issues in the system, but that is not the tanks fault, or responsibility That is on the installer.

If the system pressure and tank pressure are 12 psi, then there is no water in the tank, nor does there need to be?

What "squirrely" condition would you see if the tank were empty?

Only if you pull a sub-atmospheric condition at an air vent would air be able to enter the system. My suggestion is 5 psi positive pressure at the highest point in a system. 5 psi positive at any auto air vent.

If a gauge at the very top point of a conventional cast boiler, at an auto air vent in the top of the boiler jacket for example, was reading 5 psi, and all the piping and radiation is below the boiler 5 psi would be an adequate pressure.

Some mod cons have low pressure safety switches so fill or pump ∆P needs to be 10 psi or more.

Typically fill valves and expansion tanks are factory set at 12 psi, adequate for multi level applications, the highest point about 17' (17 X .433 + 5 = 12.3 psi) above the gauge at the fill and tank connection.

Doug_7

We agree that if the system pressure and tank pressure are 12 psi, then there is no water in the expansion tank.

We seem to disagree on whether there needs to be water in the tank at all times. I claim there always needs to be water in the expansion tank, so it can do two jobs - absorb the expansion and contraction due to temperature changes and stabilize the system pressure.

If the boiler is up to temperature and the system pressure and tank pressure are both 12 psi then the tank is empty - it is as if the expansion tank was not there. Now shutdown the boiler - what happens - the system cools down, the water contracts, the pressure drops rapidly because water is an incompressible fluid which contracts and cannot be replaced by water from the expansion tank. It could actually pull a vacuum. That is the "squirrely" condition you would see if the expansion tank were allowed to go empty - rapid pressure changes.

The expansion tank has two purposes - to absorb the expansion and contraction due to water temperature changes and to stabilize the system pressure - which it can only do if the expansion tank never runs out of water.

Running the expansion tank out of water creates an unstable pressure situation. When an expansion tank is sized you take into account both the volume of thermal expansion, and you provide a heel of water for pressure stability. Slightly oversizing the expansion tank does the trick - It just works better.

hot_rod

We seem to disagree on whether there needs to be water in the tank at all times. I claim there always needs to be water in the expansion tank, so it can do two jobs - absorb the expansion and contraction due to temperature changes and stabilize the system pressure.

I see some advantage to extra fluid in the tank IF you expect temperature drop below the ambient or fill water temperature. Solar and chilled systems as I mentioned.
If you fill the boiler with 55° water it probably will not drop below that in an operating heating system. If the system temperature drops to 45, maybe you see a few psi drop on the gauge, so what?

Amtrol, Zilmet, Wessel, pick any brand, they all indicate matching pre-charge to intended fill pressure.

The caution if you over charge the tank is that you still have, or leave adequate capacity for the expected thermal expansion. How do you know or regulate how much water to over-charge. How do you assure you still have adequate acceptance capacity? Shake the tank?

A low temperature radiant, operating between 65 and 90° would see a small amount of expansion. Running a system from 65- 180 or higher obviously requires more expansion space.

I profess the system does not care if there is fluid in the diaphragm type tank as long as static fill pressure is adequate and does not drop. Unless there is a leak the pressure should not drop.

One condition where I have over-charged a tank is a brand new system which still has some entrained air coming out. If the fill valve is left off as 50% or contractors do, then that over pressurization will assure that the air purged out is replaced with water and not drop the fill below the required static. It's a guess at best, but a little piece of mind.

If the fill valve is left on, as I recommend, no need to over-charge the tank.

If a fill valve left on frightens an installer I suggest a fill tank like Axiom:)

Doug_7

Ha Ha - Funny one hot_rod - but you're not going to trick me into trying to shake my expansion tank, when I can easily tell from the pressure gauge exactly how full it is. Besides it is too heavy.

We provide expansion tanks that are correctly sized for both thermal expansion and to provide the heel of water necessary for system pressure stability. The system is designed to operate for years with a stable operating pressure, without water addition, and with the water fill-valve firmly closed.

Nice of the suppliers of expansion tanks to do the thermal-expansion calculation for you - but there is a lot more to it than that.

We do not leave water fill valves open because of the risk of a catastrophic water leak. I recently installed a new expansion tank in a building that had such a catastrophic water leak 25 years ago, when one of a thousand connections on the original installation failed catastrophically and leaked hundreds of gallons of water. That was 25 years ago on the original installation. The continuous water supply from the open water fill-valve flooded and ruined the flooring in all 3 floors of a newly occupied residential building. $$$

Naturally the connection that failed was the 3/4" water supply to a fan-coil on the third-floor, and naturally it happened at 3 AM. A 3/4" compression fitting popped off. The one fitting that had not been properly tightened to manufacturers specifications and checked with a Go-NoGo gauge.

Owners never forget such major property-damage incidents. Very infrequent but very destructive. So if you leave the fill valve open, you are taking a known risk. Just make sure the owner is informed of this risk in writing and your liability insurance is paid up.

Lots of pros leave water fill valves closed for good reason. Our service company wouldn't have it any other way.

hot_rod

Is it possible your over charge into the exp tank is causing the squirrley pressure variations you witness as it heats?

Looking at a #30 Extrol, it is a 4.4 gallon tank with a 2.5 gallon acceptance.
The manufacture doesn't want the bladder pushed more than 50- 60% which is where the acceptance number comes from. Different opinions on that %, 60% is a bit too much IMO.

4.4 X 60% = 2.6 gallon. Pushing the diaphragm beyond that really shortens the life of the diaphragm/tank.

Installers like to complain that tanks have been cheapened and fail more often, I suspect most, many are improperly applied and adjusted.

So suppose you are charging 1 gallon into the tank for your reserve, you acceptance is now 1.6 gallon. Use actual numbers if you have them.

A system with 50 gallons of water, filled with 50° water, heated to 180, needs 1.3 gallons of acceptance. So your pressure increase will be higher, quicker, more squirrley as you reduce the size of the expansion tank by over-charging it.

Another option is the #60 tank. Notice the tank is much larger 7.6 gallons, but acceptance is still 2.4. This is because the diaphragm is crimped into the tank in the same place as the #30.

However, you have a much larger air space below, so you lessen the pressure variation as the water heats.

If you glycol your systems the numbers change, 50% glycol in that same 50 gallon system requires 2.1 gallons acceptance, getting tight on a #30, probably going to pop a 30lb relief
If you add that " 1 gallon reserve". Your tank is now under-sized.

Bag or bladder type expansion tanks can take near 100% acceptance.

After 40 years of hydronic work I got my hands on the Amtrol Engineering Handbook and learned a lot about the theory, concepts, sizing, application and troubleshooting of compression, bladder and diaphragm tanks. I think an online version is at the Amtrol site.

It should be required reading along with "Pumping Away" for all hydronic folk. Both talk about the importance of Boyles Law for tank sizing.

Good reads both, to share with your team.

Pros and cons on leaving a fill valve open. All hydronic system continue to eliminate as the heat and cool throughout the season. Systems with ramp style purgers are never 100% air free IMO, no way to eliminate the micro bubbles.

So as air purges out your extra reserve in the tank gets used, more air out now you have no way to add water. That turns into a call back, possibly a no heat call if the boiler has a 10 psi pressure safety.

A compromise is leave the valve open for a week so the system can adequately deareate, but until the temperature ramp up you will not get all the small bubbles eliminated.

I have no problem with some extra fluid in the tank as long as you know the tank is sized adequately. I promote that on solar thermal systems. Our packaged solar thermal systems held 6-8 gallons of glycol, we included a #30 tank to allow for the over-charge and the wide temperature swings.

I think we just have a difference of opinion what the tanks job is.

Accept the heated/expanded water, up to the acceptance number, while staying 5 psi below the relief setting. The Net Expansion tables are handy for this.

Have an adequate air charge to push that water back into the system as it cools and contracts.

Anything else the tank "seems" to do to the system, is more than likely an application issue. Pumping at the expansion tank for example.

It's not about squirrels
`

Doug_7

Is it possible your over charge into the exp tank is causing the squirrley pressure variations you witness as it heats?

My statement on "squirrelly pressure variations" was in direct reference to the system you mentioned where the static pressure in the boiler is 5 psi and the tank pre-charge at 12 psi. That system will have "squirrelly pressure variations" bouncing between 5 psi and 12 psi because that expansion tank is empty of water - an operating condition that we would not allow.

I do not have squirrelly pressure variations - by design I have rock-solid steady boiler system pressure.

This is the direct result of correctly sizing the expansion tank to maintain a heel of water at all times, in addition to having the required capacity to absorb the thermal expansion at design conditions. With our correctly sized expansion tank, we have the same boiler pressure, day after day, week after week, month after month. Designing one expansion tank to do two jobs seems smart to me.

Rock-solid steady boiler system pressure is exactly what we want. We don't want the fill-valve left open because of the risk of water damage, and we don't want to have to frequently check the boiler system pressure in case a small water leak develops.

I think everyone understands these two different design philosophies - fill-valve open / fill-valve closed.

It's definitely not about squirrels

hot_rod

My statement on "squirrelly pressure variations" was in direct reference to the system you mentioned where the static pressure in the boiler is 5 psi and the tank pre-charge at 12 psi. That system will have "squirrelly pressure variations" bouncing between 5 psi and 12 psi because that expansion tank is empty of water - an operating condition that we would not allow.ll pressure, then addition pressure above the pre-charge will allow water into the tank

5 psi system pressure was just for the example of how water would go into the boiler/system up until it reached the tanks pre-charge. Water would only go into the tank if the fill pressure exceeds the tanks pre-charge.
A 12 psi fill valve setting will not push any water into a 12psi pre-charged tank. At least in a tank where the diaphragm exposed area was equal on both sides. (Fire protection dry valves excepted) Agreed?

If the tank is empty, no water in it, at 12 psi pre-charge, static fill at 12 psi and the fire turns on, pressure rises, once it rises above 12 psi only then will water be pushed into the tank. An empty tank has the published full acceptance.
Pressure should rise steadily as long as the boiler is heating.

The tank pre-charged to a pressure, say 12 psi and the fill valve set at 12 psi is what the tank manufacturers recommend. Any installer reading the installation instructions, would tend to follow that procedure. Any trainer explaining expansion tanks setup would use that manufacturers suggestion.

That leaves us to the last point, there does not need to be water in the expansion tank for it to do its job properly.
The people that build expansion vessels tend to agree, as they all state that in the install sheets. If they needed to have some water in the tank to work properly, accurately, wouldn't they tell you that?

I believe your point is the system will vent some additional air, and that added water in the tank prevent pressure from dropping. Basically doing the fill valves job

You are using your tanks as a small volume, small capacity fill valve, is that the "dual purpose"? A tank with a 2.6 acceptance, how much water do you put or allow into the tank? An additional gallon, or ounce

Doug_7

Of course there does not need to be water in the expansion tank for it to do its job of protecting against thermal expansion. The expansion tank manufacturers are selling expansion volume - nothing else. No one is arguing that point.

There is no additional air to vent - the boiler water system is kept liquid-full. Sucking in air is a no-no.

Make-up water goes only to the expansion tank, because that is the only void space - the boiler is full.

I think everyone understands the implications of leaving the fill-valve open or closed - Your choice.

We choose to leave the fill-valve closed and we like the pressure stability provided by designing for an additional water volume in the expansion tank - Our choice.

End of story.