0psi cold fill pressure and 20psi while running

extrol60

I have a Lochinvar boiler WHB199N that's been working great for 4 years for radiant in-floor heating, and the expansion tank was just replaced from a Cash Acme T60 to an Extrol 60 Pro of the same size.

The Cash Acme was very old and kept the cold and hot pressure at 12psi. It was swapped out due to age. The new Extrol Pro ran at 20psi at 140F when the contractor left. I didn't see the cold pressure until 2 days later at 0psi at 90F. It seems really low, but nothing was leaking.

When watching the pressure gauge while the system kicks on, the pressure rises steadily to 20psi and stays there. I conjecture the pressure tank is set to 20psi and limits pressure to 20psi when hot, but I don't understand why it drops to 0psi about an hour after the boiler stops running. The temp/pressure gauge is at the boiler outlet.

I have added water once, and the pressure limiter keeps it to 13 psi and the gauge shows 13psi. After the system cycles, it goes back to zero. Any ideas what to do here? Thanks in advance for your help.

neilc

post a picture showing the new tank, circulator(s), and boiler, all in one shot,
any chance a isolation valve to the tank was left closed ?

STEVEusaPA

Did you check the pressure of the tank before installing it?

Jamie Hall

Any water out of the pressure relief valve?

When the new expansion tank was put in, did they make sure that the system was completely purged of air?

And don't assume you don't have a leak of some kind. Run the pressure up to 13 psi as you have done, cold, and then close the manual feed valve so the pressure reducinb valve can't maintain pressure. Come back two hours later and check the pressure. It shouldn't have budged.

extrol60

neilc said:

post a picture showing the new tank, circulator(s), and boiler, all in one shot,
any chance a isolation valve to the tank was left closed ?

All valves look open. Here are the pics. The in/out to boiler goes through the right wall of the tank/circulators.

extrol60

STEVEusaPA said:

Did you check the pressure of the tank before installing it?

Pressure is factory set to 15psi at sea level and is 20psi at current altitude. The hot temp max of 20psi reflects the tank set pressure.

extrol60

Jamie Hall said:

Any water out of the pressure relief valve?

When the new expansion tank was put in, did they make sure that the system was completely purged of air?

And don't assume you don't have a leak of some kind. Run the pressure up to 13 psi as you have done, cold, and then close the manual feed valve so the pressure reducinb valve can't maintain pressure. Come back two hours later and check the pressure. It shouldn't have budged.

I didn't watch the job as these are my long time plumbers. I don't hear any gurgling. No spewing/dripping from micro bubbler.

@Jamie Hall I ran the pressure up to 13psi with the system off, then turned off the external water input valve. When system turned on the pumps, the pressure drops to 5psi (equalizing) before it heats up and reaches 20psi. Then when it cools down to 100F, pressure drops to 0psi. Thoughts?? Thanks.

neilc

extrol60 said:

All valves look closed.

open, all valves look open , , ,
and I don't see any isolation for the tank,
so,
as per Steve's's question, was the tank checked for precharge before installing?

extrol60

neilc said:

extrol60 said:

All valves look closed.

open, all valves look open , , ,
and I don't see any isolation for the tank,
so,
as per Steve's's question, was the tank checked for precharge before installing?

Typo, sorry. Pressure is factory set to 15psi at sea level, which is 20psi at current altitude. The hot temp max of 20psi reflects the tank set pressure. I don't know if it was checked.

neilc

with that leaking air separator, and that bandage hose, is that air vent still open? are you sure?

extrol60

neilc said:

with that leaking air separator, and that bandage hose, is that air vent still open? are you sure?

Thanks for the quick replies @neilc The micro bubbler hose is dry (maybe just a fail safe). I checked several times while the system is running and not running. How do I check if the air vent is still open? Is it the white thing at the bottom right of the pic? I don't see or hear anything.

neilc

I am refering to the micro bubbler air vent,
where that hose doesn't belong,
though if you had air up there you would have different issues, so, nevermind.

extrol60

As a general question, should the expansion tank precharge be set to a similar pressure as the fill limiter, or should it be higher?

For example, my fill limiter goes to 13 psi but the expansion tank is (probably) 20 psi. I think the previous tank was more like 13-15 psi.

neilc

the tank air pressure, and the system cold water fill pressure should match, 12, 15, 20is a little high unless you're 3 floors up,
tank needs to be checked while it's disconnected from the system pressure,
and none of this explains why your cold pressure is at 0(zero).

EBEBRATT-Ed

@extrol60

Factory setting. That is what your not getting.

The tank is supposed to be set at 15psi from the factory. If the plumber did not check it before he installed it (and many don't) then there is no way of knowing what the pressure in the tank is. It could be a bad tank. It might have the wrong air charge from the factory. At this point everything is a guess.

But pressures changing point to an expansion tank issue.

The tank should be taken off and the pressure checked. It must be disconnected from the system or isolated from the system with no water pressure on the bladder to check it.

The pressure should be set the same as the water feeder....usually 12-15psi.

Best practice is to install a ball valve between the spirovent and the tank so it can be isolated and a drain valve installed between the new ball valve and the tank.

extrol60

neilc said:

the tank air pressure, and the system cold water fill pressure should match, 12, 15, 20is a little high unless you're 3 floors up,
tank needs to be checked while it's disconnected from the system pressure,
and none of this explains why your cold pressure is at 0(zero).

I don't normally have the auto fill connected. I only fill it when I see the pressure is lower than 13. Before this expansion tank change, I top it off maybe once every 6 months (pressure was really constant).

Could it be that the system just doesn't have sufficient water? Given I can't add any water past 13 psi and the running pressure is 20 (goes immediately to 20 psi when the recirculation pumps kick on).

hot_rod

Looks like you don’t have a fill system connected. I see a Caleffi fill valve and backflow. Looks like a hose valve on the backflow inlet. Like you need to connect a garden hose to fill.
The system needs cold fill pressure to 12 psi

neilc

but before you jack the water pressure up,
and while it's reading 0,

check the air pressure at the tank, set it to 12, 15, whatever you intend to fill the water to,

Jamie Hall

It is also remotely possible that you have a lot of air in there somewhere. That could, quite easily, bring the pressure down to zero as it cools off.

At this point, it might be interesting (?) to bring the installer back and ask him or her to explain why the system pressure doesn't hold as it should. Let us know what he or she says...

jeff4444

I just had a similar experience with the pressure going up at higher temperature and down, way down at cold room temp. My case it turned out the pressure gauge itself as bad.  Search for my recent post. I replaced the pressure temperature gauge for $35 at Home Depot. Don’t know if it’s the same problem but that’s what I had.

extrol60

hot_rod said:

Looks like you don’t have a fill system connected. I see a Caleffi fill valve and backflow. Looks like a hose valve on the backflow inlet. Like you need to connect a garden hose to fill.
The system needs cold fill pressure to 12 psi

@hot_rod Good eyes on the Caleffi, and then I see you are their trainer. The vent bleeds water when I leave the fill hose attached. Is there a quick fix for that? Thanks for your help.

EBEBRATT-Ed

You would have to replace or rebuild the backflow preventer to stop the leak.

hot_rod

Fairly simple to disassemble and clean. There is a check in the very end of the fill valve also. It should hold so you could remove the entire BFD to clean, without loosing system water.

The first seal to be made when water enters, the cartridge slides to close off the vent opening, see example. If it drips right away, something is stuck in that spool /seat.

Then the two checks pop open to allow water into the system.
Most often a piece of crud in one of the checks.

If any of the seals have a nick or chunk missing in the seals, replace the assembly.

Notice the label is riveted on. If someone plugs the vent port and the valve has failed, it will seep from the rivet holes to indicate it failed.

But don't plug the vent hole! Ideally it is piped to the floor, as per code.

extrol60

Thank you everyone for your detailed help and timely replies to resolve my boiler pressure swing issue. I am documenting below for future readers.

It appears the Extrol 60 Pro tank was set to factory default of 15psi, which is 20 psi adjusted for altitude. Plumber didn't set it to match limiter pressure. The symptom is pressure goes to 20psi when heating and to 0psi after it cools off.

The reason... Since cold fill pressure limiter is set to 12psi, and the pump traps the 20psi water/glycol in the zones when the zones turn off, the rest of the system is starved and goes to 0psi. This resolves as soon as any zone turns on equalizing the pressure.

Also, leaving a hose attached for autofill only hides the problem at hand, but you still see the pressure swings if the delta between tank and limiter pressure is more than 1-2 psi. I personally believe letting pressure swing widely between cold and hot will degrade your tank's diaphragm much faster.

extrol60

hot_rod said:

Fairly simple to disassemble and clean. There is a check in the very end of the fill valve also. It should hold so you could remove the entire BFD to clean, without loosing system water.

Thank you @hot_rod for the complete instructions on cleaning.

neilc

still makes no sense that you have zero, then 20, when heating,
did the old tank do this?
get another gage on there somewhere,
cold fill to 12,
if it climbs to 20 when heating, then you're still ok,
or the tank is preset higher than the 12,

extrol60

neilc said:

still makes no sense that you have zero, then 20, when heating,
did the old tank do this?
get another gage on there somewhere,
cold fill to 12,
if it climbs to 20 when heating, then you're still ok,
or the tank is preset higher that the 12,

Here is my thinking on why the problem happened. When the expansion tank was set to 20psi, it wasn't really doing anything (other than limit the max pressure to 20). Because my fill is limited to 12, I can't get enough water into the system to be anywhere near 20 psi.

The system has 3 circulation pumps, all with internal check valves. In particular, the pump that feeds the heating zones is the biggest and all the zones have cutoff valves (set by the thermostats) on the return side. When heating, I can hear the cutoff valve(s) close before the circulation pumps stop. That seems like it would build a lot of pressure in the zones and then trap it there (all cutoffs are off, and the pump check valve will prevent backflow. Thus the heating zones (which are the majority of water volume) at pressured up while the feedthrough loop is likely a little starved of water and thus pressure. At the same time, the expansion tank has nothing to give back because it's set too high and always empty. So the loop with my gauge shows 0 psi.

As a test, I manually clicked open one of the zone cutoffs and the gauge jumped up to like 17 psi. Clearly pressure/water was being trapped.

Anyway, when I set the expansion tank equal to the limiter, it started storing some water as intended and that expands back into the feedthrough loop after the zone cutoffs click off. Hence the pressure seems to be more constant.

Maybe this theory holds water

hot_rod

Unless you have checks in the pump and also on each return, you cannot trap pressure in a zone or circuit. The other end, the return end is open to the rest of the system.

Static fill pressure of 12 psi at the boiler gauge.
static pressure will be a bit lower as you go up, a bit higher if you have piping below the gauge.

.433 psi for every foot of elevation change. so 10' above the gauge the pressure will be 4.3 psi lower
.
So for multi level homes, 12- 15 psi is adequate.


Here are the water expansion tables.
If you fill with 50° water and heat it to 180, the factor is .02757

If your system holds 35 gallons of water 35 X .02757= 2.4 gallons of acceptance volume. A #30 tank is plenty large enough.

If you know your system volume, enter that number,

EdTheHeaterMan

I wonder why there are 2 boiler pumps and one system pump? (Pumps A and B ) Perhaps the IFC check valve on one of the boiler pumps is keeping the water pressure in the system disconnected from the boiler pressure gauge. I would need to draw the system on paper top see if that is the case. That could be problematic if the zone3 valves are working against that pressure. The test that @extrol60 did by opening a zone valve and the pressure got released to the boiler gauge is pretty conclusive in my opinion. IFC on the system pump at the supply side and the zone valves at the return side, could lock that system pressure in.


I had to help a friendly competitor with a similar problem. He replaces a Taco 007F5 with a Taco 007 IFC and the system locked up. Zone valve would not open as a result of the hot water in the baseboard radiator being isolated by the IFC valve and the zone valve. After the water cooled down there was such a vacuum created in the baseboard rads that the zone valve motor was not strong enough to open the valve. (I think the zone valves were on the supply and the pump was on the return just the opposite of yours)

The fix for that job was to remove the plastic IFC from the Taco 007.

Your fix is to get the expansion tank to be the same pressure as the fill pressure (as it should be).

SuperTech

Is there enough room to install the expansion tank so it's vertical? I hate seeing sidewards expansion tanks. Every time I come across one on the job it has a failed bladder/diaphragm. 

extrol60

hot_rod said:

Unless you have checks in the pump and also on each return, you cannot trap pressure in a zone or circuit. The other end, the return end is open to the rest of the system.

The return end is trapped by those silver rectangular box-like valves, which is electronic. They close when a zone turn off and opens when on. There is a manual override on each one, and opening one can equalize the pressure from 0 to almost 20. That's how I figured out how the zones are trapped. Perhaps a safety feature?

I like the expansion table. Thanks.

extrol60

SuperTech said:

Is there enough room to install the expansion tank so it's vertical? I hate seeing sidewards expansion tanks. Every time I come across one on the job it has a failed bladder/diaphragm. 

Not really. Space is very limited. I wonder why the horizontal ones fail. Is it because the diaphragm becomes lopsided and stretches unevenly when it fills?

hot_rod

Really no need for the checks in the pumps if you have zone valves on the supply. Unless there is some odd piping that could cause reverse flow. Hard to see what is missing in the rest of the piping

Nipple up is preferred mounting for the tank. All the manufacturers now show horizontal mounting as an option.

Good, better, best. Nipple down, horizontal, nipple up.