Heating System Pressure & Temperature FAQs

Boiler Pressure Too High FAQs
Boiler Pressure Too Low FAQs
Boiler Temperature Too High FAQs
Boiler Temperature Too Low FAQs

Boiler Temperature Too High FAQs

My house gets too hot after I replaced my Primary Control Aquastat - the aquastat won't allow a low-enough setting

My home heating system boiler was working fine until I had to replace the controller with Honeywell Aquastats .

Now the house gets too hot .the radiators they become too hot .my old regulator was set at 180.

However the Honeywell Aquastats the lowest range is 220F. How can fix this issue .thanks On 2017-02-18 by Al

by (mod) - no you've mis-read your manual - start by checking your thermostats

Al

What you describe doesn't sound right to me. There is no heating boiler aquastat whose LOW end is set so high as 220F.

Furthermore, it's the room thermostats that control room temperature. Start by checking the thermostat settings and compare those to room temperature.

If room temp goes above the set temp on the thermostat then a check valve or zone valve a the boiler may be stuck open.

Detailed help you need is at

AQUASTAT HI LO DIFF SETTINGS

and

THERMOSTATS, HEATING / COOLING - home

Buderus Hydronic Boiler GC144 overheating problem

My new Buderus Hydronic Boiler GC144 seems to be overheating water in the Economizer Mode. I hear popping noises from boiler and see water temperature going to 248F after the burner stops.

The circulator is not running in Economizer Mode, and I can not set Economizer to OFF.

Technicians that have come out say that it must be air in the system, but I think water is boiling in bottom of boiler. I have purged air from system and see no difference.

I have no problem with the heat circulating thru the system with a normal call for heat when the circulator runs. Suggestions on what to do next? On 2018-11-11 by John M

Reply by (mod) - problem with the boiler's aquastat or its sensor

John

For normal hydronic heating boiler,

Something certainly sounds wrong with the aquastat or boiler controls. It would be quite unusual for a boiler to reach temperatures over boiling.

That would mean that the system is under pressure and that the control high limit is abnormally High.

In fact I wonder why the temperature and pressure relief valve isn't opening.

It's possible that this is an unsafe condition. Have you tried giving a call to the manufacturer's technical support line?

by John M: Problem was improper plumbing: the installer reversed the supply and return lines to the boiler.

Thanks for your quick reply. I also believe that I found the problem. The installer has reversed the supply and return lines to the boiler.

As installed right now the temperature sensor on the Aquasmart is reading the cold return flow from the baseboards, not the hot water exiting to heat the house.

This is causing the sensor to confuse the Aquasmart. I have already placed a call to the installer to contact me. Thanks Again John

by (mod) - Buderus Hydronic Boiler GC144 overheating problem solved!

John

Nice going. Let me know what the installer says when they show up. Your comments and troubleshooting will surely help other readers so I'll be sure to keep this information around. Thanks again for the follow-up.

What happens if the boiler high limit switch isn't working.

What is the problem if my hot water heating furnace high limit switch is not working? - (June 21, 2012) abbas

On my 10 year old hydronic residential boiler, I replaced the feed water regulating valve and backflow preventer, and relief valve. On a well water supply these parts were boogered up.

I adjusted the new feedwater psi to 12lbs. My expansion tank had 28lbs?(don't know why) I reduced the tank pressure to 12lbs as well. I didn't notice any water coming out of the schrader valve, so I assumed the tank (bladder type) was ok.

The boiler has a tankless heater coil for domestic hot water.

My perimeter heat has come on only twice so far. Since firing the boiler back up I noticed the pressure has creeped up from the cold 12psi to around 22psi.

This is over two weeks now. My aquastat settings are 160 and 180 with a 15 degree differential. And these settings are working fine. My relief valve weeped prior to the adjustments with the feedwater valve and expansion tank pressure.

My concern is, at boiler shut off temp of 180 will the boiler pressure level off close to 30psi.

Again, I'm at around 22psi now. The expansion tank was the only external componant not replaced. Thank You, John P (Sept 20, 2011) John

I just want ask : what type of gauge can be used to measure pressure and temperature on a heating boiler? (Apr 1, 2012) Muhd Nazlan from Malaysian s

Reply: high limit switch not working means the boiler is unsafe

Watch out: Abbas the problem with a Hi Limit switch that is not working is that the boiler is unsafe and can overheat, damaging or even ruining the heat exchanger.

If on a residential hot water heating system you see boiler pressures over 30 psi or temperatures over 200 degF, you should turn the system off and call for repair.

Our thermostat is turned down but our hot water heater won't turn off

Thermostats turned all the way down, 89 degrees outside, baseboard heaters are hot why is that? Is there a way to prevent those from heating making the house hotter than it needs to be? Not to mention burning gas and running up that bill? On 2017-06-14 by Chris

by (mod) - probably not an aquastat problem

Chris

Sounds like a zone valve stuck open or a check valve at the boiler stuck open. Use the on-page search box at the top or bottom of this page to find our article on

• HEAT WON'T TURN OFF

to read details, please take a look at that article, then ask more questions as you need.

by Chris

I have no clue what it is I'm looking at on this boiler. Is there a way to shut the water off to the baseboards without shutting off the bath hot water.

At least until my landlord get here to look at this? 90 degrees in the house in June at 9 o'clock at night is simply not acceptable.

Boiler overheats at end of call for heat

Hi, I have a hydronic boiler with lots of zones one of which is for the indirectly heated hot water system.

When the flame goes off and all zones are off, the boiler which operates at about 55C or 110F starts heating up and sometimes vents at the overpressure valve.

What could be causing this "latent" heat? I suspect either air in the top of the boiler or gunk in the bottom but I have tried to get rid of both, if there was any.

If I could add a "run-on" or "cool-off" time to the water pumps (of which there is 3) then the problem would be solved. (Nov 28, 2012) OsK

Reply:

OsK,
Thanks for the helpful comment on radiator & piping temperatures. I agree.

It is also helpful to feel comparable temperatures. For example, I (carefully as surfaces can be quite hot) touch and compare pipe temperatures on the inlet and outlet sides of a zone valve or a (quiet) Taco circulator to see if the valve has opened or the circulator is running.

Indeed for some applications we need to read temperatures more accurately, or we may even need to use thermography or other large area scanning tools (like finding where there is a break in readiant heat tubing in a floor), but just to see if something is open or working, the simple temperature comparison should be enough.

Finally, at least with some themographic equipment such as my Exergen scanner, the temperatures given on the digital readout are NOT accurate unless you are reading at the proper distance and from a flat black surface. Exergen even included a black crayon we use to make a mark on a shiny surface when we're looking for more accurate numbers.

We appreciate your helping-out OsK - together we are smarter than any individual.

...

OsK

About that odd hot boiler, I agree that it's an unacceptable condition, and regular spilling of a TP valve can be dangerous for some reasons beyond the obvious.

Is it possible that the boiler in question uses a tankless coil that is leaking into the boiler, increasing its pressure or even causing it to cycle on?

If not, check
- using our pipe feeling discussion, is there actually hot water from somewhere draining back into the boiler? (A bad check valve or zone valve?

- the primary control temperature sensor - is it properly placed, using the manufacturer recommended thermal grease, and working?

- the primary control itself

- or of course the problem might be something we haven't though of or can't see via just e-chatting

Exactly how hot should heating radiators actually get?

Exactly how "hot to the touch" should radiators get? Do you define hot to the touch as can't touch them for more then 5, 10 seconds? My radiators get luke warm (not "hot" to the touch)after the boiler has been running. (Nov 29, 2012) Craig 

Reply:

Craig, your definition of hot to the touch seems about right. Luke warm is ok if it is the last radiator in a long series chained together. If the input side of the radiator is warmer than the output then the radiator is doing its job radiating heat.

If the output of the boiler is too hot to touch and the return is cool, then the heat is being transferred to the radiators and hopefully making the rooms warm. If the return on the boiler is also hot while the radiator remains luke warm then there is a problem. I go around and check the radiators with my hand but I also use this temperature tool

- Mastercraft Digital Temperature Reader available from Canadian Temperature

by Craig

Hey Dan, Thanks for the response. The output is "Warmer" then the input, so I can say with confidence that it is circulating. However, the output right at the boiler, but I can hold it indefinately (its not too hot). I also came across a post regarding the expansion tank (old big steel kind above boiler), if it has water in it to empty it (about 40+ gallons removed) and it would recharge about 11 gals.

I then ran the boiler for 2 hours now and the output is still not very hot to touch. So recap- 1.burners are working fine, 2. the circulating pump seems to be working, 3. the expansion tank has "air cushion," and the thermastat at the burner control is on max.

Here it is really bizarre, I can touch the cast iron heat exchanger on the sides no problem, you would think that all the cast iron on the exchanger would be red hot when being cooked for 2 hours???? In the end the room temp maintains 68, I just have a gut feeling it isn't working they way it is suppose to be. BTW thanks for taking the time with managing this site, very helpful!

The output pipe is hotter then the input, I can say for certain the circulating pump is working, but even right at the boiler the output pipe isn't that hot, I can grab it right at the boiler for any amount of time. Crazy is the burners are working and the thermostat is on close to max

. Further, the cast iron heat exchangers aren't that hot on the sides. You would think the anywhere on the exchanger would be red-hot after cooking for hours. Today I emptied the 40+ gals. of water from the expansion tank, when I turned on the water again, the tank filled w/ about 11 gals. (watched water meter).

So pump works, burners work, expansion tank has "air cushion" but the output pipe and radiators are not that "hot" to touch. Thoughts? Thanks for maintaining this site, very helpful!

Reply:

Craig a waterlogged expansion tank causes relief valve spillage, not indequate radiator heating.

A radiator that is just warm is probably not getting enou heat delivered

Partially air bound or piping uninsulated or temps set too low, or rad valve partly shut
Etc.

Figure water leaving the boiler is 180 and maybe 140 at a radiator - bllpark,
It would feel quite hot, not ... Warm

Boiler Temperature Too Low FAQs

What are the right Lochinvar model RBN 135 serial d029094 aquastat settings

Lochinvar model rbn 135 serial d029094

My operating temp dial is set at 180 and my hi limit dial is set at 200

The boiler temp only gets up to 130-135 then kicks off untill it reaches 120 then kicks back on psi is steady at 20 all the time

I have a new circulator pump, new expansion tank, new auto fill valve. - (Feb 16, 2014) henry

Reply: aquastat settings may be wrong

Henry

Check the aquastat settings: someone may have set the LO limit too close to or even above the HI limit. If the settings are correct then I suspect a control or control sensor problem.

Our diagnosis and setting details for aquastats are

at AQUASTAT HI LO DIFF SETTINGS

Our boiler doesn't get hot enough - what do I change on the Aquastat?

I wired the boiler aquastat into a relay transformer system with circulator.

I have a Weil / McLain boiler with 2 zones using a what appears to be a 8182D Aquastat controller. I rewired things so that the thermostats control only the circulator on each zone respectively.

Since doing so the boiler seems to keep the temp at the low setting (140F) only and does not ever reach the hi setting of 180F.

What changes do I need to make so that the burner fires at 140 and turns off at 180? On 2018-12-22 by George

Reply by (mod) -

George, try the aquastat setting suggestions at

AQUASTAT HI LO DIFF SETTINGS

Boiler Pressure Too High FAQs

Boiler pressure too high, relief valve spills - getting to the root of the trouble

My boiler pressure has been reaching about 32 and relief valve has been releasing water I replaced valve then noticed pressure was exceding valve pressure expansion tank is fill-trol 110 the air vent seems to be releasing water occasionally do you think it is the expansion tank. (Dec 15, 2014) Roger

Reply:

Roger

You want to see this diagnostic article

RELIEF VALVE LEAKS

to get at the underlying cause: could be a bad expansion tank, pressure regulator, or other causes.

Watch out: a leaking pressure relief valve means the heating system is unsafe.

Roger said:
I turned boiler off and closed fresh water feed to expansion tank pressure was about 32 psi and stayed there for 2 hours left fresh water feed to indirect water heater open.

Water pressure from well does not exceed 72 psi

When I turned boiler on pressure rose to 35psi and back down to 30 psi while temp rose to 175 and then shut off and cools down to 120 with 22 psi and no zones on.

Reply:

Roger pressure over 32 psi is already too high in the boiler. When the boiler is COLD the pressure would normally be around 12 psi, heating up to under 30 PSI at maximum boiler operating temp. Higher starting pressure is needed for taller buildings.

With boiler cold drop pressure to 12-18 psi. Watch to see if pressure rises while boiler remains off. I understand in cold weather when you want heat this can be difficult.

If the boiler contains a tankless coil shut water off coming into the coil to see if that is the leak source.

Watch out: If your water pressure reducing / feeder valve that supplies water to the boiler is leaking or improperly set or if you manually added too much water (at pressure) into your heating boiler that could explan an abnormally (and unsafe) cold boiler water pressure.

Roger said:
I have changed the feed valve and air valve on top of separator but pressure still wants to remain around 30 my boiler is an Allied MG-100 so if i can shutoff the boiler and close the return line coming into boiler i should be able to check indirect heat water tank for leaks

Is that correct as the valves will release excessive heat will i have to take some pressure off the gauge first thanks for your patience.

Reply:

Roger

IF you set the boiler pressure to 12 PSI when the system is cold and leave the boiler off the pressure should not increase.

IF it does there is a leak into the boiler - sometimes from a leaky water feeder / pressure reducer valve or possibly from a tankless coil (or leaks into the boiler circuit heating an indirect-fired water heater) when the boiler has one.

Watch out: The TP valve releases heat and pressure trying to avoid a dangerous BLEVE EXPLOSION

Roger said:
when i drain the pressure and then open it the pressure goes to 20 psi should i have the return to the boiler open the expansion tank is new but must have 20 psi should i take some air out of it.

When I leave return open and boiler off the the pressure rises sounds like it might be the indirect fired water

Reply:

Did you tap the pressure gauge to see if it's sticking?

Roger said:
No tapping on gauge doesn't do anything I shut off boiler about an hour ago and no movement still at 20 psi where it goes when i cut in the feed valve after draining

Reply:

Roger if the gauge pressure does not fall when water is removed from the boiler, it's probably stuck or debris clogged and needs replacement. Try measuring boiler water pressure at a boiler drain using an independent gauge.

Watch out for scalding burning hazards.

Roger

gauge goes to zero when I drain boiler doesn't go up to 20 until i cut water back in

boiler just shut off at 175 degrees with 30 psi boiler cools down to 120 and now pressure is 27 boiler has been off for an hour and pressure is staying at about 27

I have replaced the expansion tank, feed valve, and air valve when i put new expansion tank in i didn't check air pressure as it was supposed to be preset amtrol filltrol but when i cut in water gauge went to 20 psi it seems that should have been 12

I can't figure why psi only drops 2 or 3 psi after boiler cools down

Reply:

Roger you'll only see 12 PSI when the boiler is *cold* and your system, if your home is 3 or more floors tall, may actually need a higher starting pressure. So when the boiler is off for an hour its temperature is still pretty hot. Still I'd think pressure would drop more than 2-3 psi.

If the relief valve is not spilling (which would be a second indicator of high pressure or temperature) I'd move on to make an independent measure of the actual boiler pressure, taking care not to get scalded.

At inspectapedia.com/water/Water_Pressure_Measure.php we show how you can buy or make an inexpensive independent water pressure test gauge that would work on the boiler drain - provided your boiler drain can be opened and shut without leaking.

Roger

the relief valve is spilling the house is a ranch with boiler in basement it really seems that the gauge is accurate the spillage doesn't occur until gauge reaches 30 which is valve setting

Can i close the return from indirect water heater and close zone valve to water heater to check for leakage from water heater into boiler circuit and turn boiler on it would be isolating the water heater from boiler

Reply:

Roger,

You should indeed be able to isolate the indirect water heater from the boiler - as the water heater too has its own pressure relief valve.

Heating Boiler pressure keeps climbing too high?

So the boiler was left cold overnight and the pressure was set at 12 PSI. 4 hours later it was at 16 psi.

Pressure was dropped back to 12 and about 4 hours latter it was 17. I dropped the pressure again and when I awoke at 11 AM it was at 18 psi.

So I dropped the pressure again to 12 and FIRED the boiler up. When I came back 30 minutes latter the boiler was at 17 psi. For grins I closed off all the heating zones at the returns using 2 ball valves. I left it this way for just a couple of minutes.

As soon as I opened the ball valves the pressure dropped from 17 psi to 4 psi. (yes 4 psi). (Aug 19, 2014) Donald Fletcher

Reply: boiler pressure and temperature increase are normal when the burner runs

Donald

Of course when the boiler is heated the pressure will increase.

When you left the boiler off did you shut off its water feed valve supply? If so, and pressure increased, either the valve didn't close fully (and the water feeder was overfeeding) or there is a leak into the boiler.

Opened what ball valve? The boiler water feeder? (you could also have a failed water feed valve)

Watch out: a tankless coil leak on a boiler will feed water into the boiler at house pressures and will cause over-pressure and unsafe conditions risking a BLEVE explosion.

By Donald Fletcher

YES, the water feed valve supply ball valve was closed (I call it a street fill valve). After that there is a BFP [Backflow Preventer Valve] and after that there is a pressure reducer auto feeder.

If the water is coming from the water feed valve supply it would mean the auto feeder is bad as well as it should not allow more water in. It's a 14 PSI auto fill valve.

After I fired the boiler up, 30 minutes pressure was at 17 psi. I closed the off the heating zones by closing the ball valves of the return side off the zones. When I opened those return side ball valves a few minutes latter the pressure fell to 4 psi. So I have no idea whats up with that. I have not been able to duplicate that pressure drop.

I will change the water feed supply valve and close it and repeat test tonight. If pressure still rises I will install new indirect water heater. I am still not confident the water heater is the problem though.

Reply:

Just being complete.

I suspect a coil leak into the system.

Donald Fletcher

Thanks again for your help. :)

Here's where I am with this. I replaced the street fill valve as a matter of course since the handle was broken and I wanted to eliminate any issues. The boiler sat overnight off and in the morning it was 100F.

I took enough pressure off so I could check expansion tank again, which proved out at 13PSI. I let the pressure reducer auto feeder valve fill the boiler back up. My 0-30 lb pressure gauge read 12psi. I left it like that, with the boiler off thinking I would see a pressure rise in a few hours. When I returned 2 hours later the pressure was 0 psi.

I opened the street water feed supply and again the pressure reducer auto feeder brought the pressure back up to 12 psi. 2 hours later it was 4psi. I filled the boiler again (12psi) and fired the boiler up. When hot, I turned all heating zones on, and I bled them but there was no air.

The boiler never returns to 12psi when cold. When cold its more like 17psi and when hot it's 18.5 psi. To my mind when cold it should go back to 12psi or at least very close to it. If the indirect water heater coil has a pinhole then my 60psi streetwater should have drove the boiler pressure past 30psi and tripped the 30psi pressure relief valve.

So for Wed night & all day yesterday and today the pressure has been the 17-18.5 psi I mentioned earlier. -(Aug 22, 2014) Donald F

Reply:

Donald

If the boiler "sat overnight" in an OFF condition I'd be quite surprised for it to be at 100F unless your home is over a thermal spring or something. Overnight with heat off I'd expect the boiler to be at room temperature (say 60 to 65 degF) and the boiler pressure to be down around 12 psi (for a 1 or small 2 story house).

I don't quite understand the combination of 100 degF and 12 psi. Perhaps these gauges are off, stuck, debris clogged, broken.

Then you left the boiler turned off and pressure dropped to zero - that sounds like a leak.

It's possible for boiler water to leak out if its pressure is above street pressure inside a coil, and to experience a leak in when street pressure is above boiler pressure.

Certainly though, if the boiler is shut off and cold it ought not drop to 0 psi.

Are there flow control valves or check valves on this system. Might one or more be sticking?

Donald F. said:

Just normally closed heating zone valves at the return side and ball valves on the supply side.

These ball valves are left open year round. A BFP and the pressure reducer auto fill valve. Both the BFP and the auto fill are out of the equation because 1st in line street fill ball valve is closed.

It did not lose pressure overnight. It was 12 psi when I went down there. I lowered the pressure to 0 to check expan tank, which was at 13 psi. I then represurized the boiler to 12 psi and 2 hours latter it was 0.

Tonight however the boiler gauge on the boiler to sustem side is reading 24psi and my master 0-30psi gauge is reading 21 so if this continues I will actually be happy because it will give more credence to coil pin hole theary.

I called the water company today and they said water pressure at their last street test 8" main was 71psi. I will continue to monitor boiler several times per day. I should have a better handle on it by Sat night. Aug 22, 2014)

Reply:

Donald,

If you stabilized the boiler at a known pressure, left it off, and made sure that no water at street pressure could flow into the indirect water tank from either its inlet or outlet piping (excluding thus backfill by gravity from above) or even more thoroughly, drained pressure off of the hot water tank,

then if there were a pinhole or larger leak into the heat exchanging coil inside the indirect fired water tank, boiler water should leak out into the water tank (contaminating it) or at best no water would flow.

Also see WATER PRESSURE TOO HIGH: DANGERS 

Why does the gauge on my steam boiler go all the way up to 18 psi

(Nov 29, 2016) joe said:
my pressure switch is set at 2 but the psi gauge goes all the way up to 18 psi - my pressure switch is set at 2 but the psi gauge goes all the way up to 18 psi is this normal

Reply:

Joe: on a normal residential steam boiler your operating pressure will be between 0.2 psi and 0.5 psi.

See STEAM BOILER PRESSURE for details.

Boiler Pressure Too Low FAQs

Boiler pressure drops to zero with the water supply turned off = a boiler leak

Can the "cold" pressure go to 0 if the water intake has been shut off (i.e. new water can not be introduced). Trying to determine if we have a leak, so we have turned the water intake off to ensure no new water can be supplied to the system.

Cold pressure starts at 12, but after 4 to 5 days it goes to 0. The boiler does run during this time.

When it is running, the pressure is either 15 or 19 depending on pump speed:

- pressure is 19 when pump set to medium position (temp rises to 150 before boiler shuts off due to temperature setting on boiler)

- pressure is at 15 when pump set to high (water temp only rises to 108 in this case).

But after 4 to 5 days, the cold pressure goes to 0. I this normal? Can it be caused by something other than a leak? (Dec 23, 2014) dean

Reply:

Dean

Cold pressure in a hot water heating boiler (hydronic) won't normally fall to zero unless there is a leak. Typically it'd be around 12 psi. A steam boiler pressure will drop to zero when cold.

I'd be looking for a leak.

Detailed help is at BOILER LEAKS, HOW TO LOCATE

How fast I can get 1 bar of pressure in my water heating tank ?

I have 10 liter capacity tank heating system..

So , I top the water until 8 liters
Below I have 3 kw heAter

Start the heater until 1 bar

Top area 2 liter volume I have
My question is how fast I can get 1 bar? (Oct 9, 2016) Poopathi

Reply:

Poopathi,

I don't fully understand your water heating system, but from just your note I don't think the pressure you seek is reasonable.

If you have a closed water tank in which you plan to heat water, and if you do not fill the tank completely, then heating water in the tank will produce only a very small pressure increase in the tank, almost below what you can measure, UNTIL you boil the water, producing steam that in turn raises pressure in the area of air above the water.

This is not practical nor is it safe for a water heating system - too hot, too dangerous.

Also your question omits some necessary data: the temperature of the incoming water, the starting pressure inside the heater (assumed 0 or 1 Atmosphere at sea level about 14.86 psi but reading "0" on a typical pressure gauge)

The article above describes pressure increasing in a fully enclosed and totally filled tank of water that is then heated.

For a FULL and ENCLOSED water tank, here is the formula describing electrical energy in watts, time, and water temperature rise:

Rated Hot Water Heat Output in Gallons per Hour = (KW x 3413) / (Temperature increase x 8.25)
or

Rated Hot Water Heat Output in GPH = (KW x 414) / (Temperature increase)

A 3 KW heater element has a rather modest heat output rate. If we have a single 3 KW heating element the calculation is

3 KW x 3413(constant) = 10,239

Assume: incoming water temperature of 55 degF.

Assume we want (because we're crazy and don't understand the danger) to boil our water: we need to raise its temperature to 212 degF.

212-55 = 157 degF; - necessary temperature rise
157 x 8.25 = 1,295.25

Now we divide:

10,239 / 1,295 = 7.9 GPH - we will require one hour to increase the temperature of 8 gallons (30 Litres) of water to boiling.

Next we calculate how much time will be required to heat up 8 litres of water to boiling, assuming sea level and the incoming temperature I gave.

8 Litres = 2.11 gallons

2/8 = 1/4, so we need about 1/4 of an hour or 15 minutes to boil 2 litres of our 55 deg water using a 3 KW electric heater.

Now we have JUST STARTED boiling the water. How long will it take for steam pressure above the water in the tank to increase pressure in the open 2 litre space to 1 bar?

1 Bar of pressure = 14.5 psi

Starting absolute pressure above the water = 1 bar at sea level
Starting gauge pressure above the water in the tank = 0 gauge pressure

To get to 1 bar of gauge pressure in the enclosed tank you will need to produce enough saturated steam in the 2 litre volume to increase the pressure to that level. (13 cu.ft. per pound) See Keenan and Keyes, THERMODYNAMIC PROPERTIES OF STEAM, by permission of John Wiley & Sons, Inc.)