Expansion tank pressure

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kyoboof

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saskatchewan
I have a Coaire Tankless water heater. It has a built in expansion tank. What should the pressure be inside of this tank?

Thanks.
 

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pressure should be set at whatever the incoming water pressure to the house is.any more questions I would call manufacture for assistance
 
Thanks so much. I had one person tell me 15-20 psi. Does that sound correct?

Ill have to buy a gauge.

I would love to be able to contact the manufacturer but they went out of business and completely shut their doors and all support. Now i'm stuck with a problem that only the kind internet folks might be able to help with.

Most plumbers i've talked to don't have a clue unfortunately and just quote me 5-6k for a new one right away.
 
May I assume this unit is not being used on a hydronic heating system in addition to your domestic hot water?
Do you have a recirculation system for your domestic hot water?
The only reason I ask is because an expansion tank isn't typically required for an on demand tankless hot water unit unless it has a recirculation system. If that was the case, it would be your water service pressure.
But if by some chance it did include a loop for a heating system then that would require an expansion tank set at the typical 12 to 15 psi.(That's probably what that person was thinking when they told you 15-20 psi.
 
33D08D07-1C3D-47F3-AA38-670623C3490F.jpeg FC24572A-F9F9-41F7-A678-C0E33D51FA38.jpeg E830E289-B846-4F4A-B95E-13C065161EA7.jpeg 33D08D07-1C3D-47F3-AA38-670623C3490F.jpeg FC24572A-F9F9-41F7-A678-C0E33D51FA38.jpeg E830E289-B846-4F4A-B95E-13C065161EA7.jpeg The tankless heater is also used to heat the house I have a life breathe furnace. It’s not just used for the domestic hot water.

Here is a picture of the whole set up.
 
Here is my original post as well describing the whole problem

“I have a Coaire natural gas tank-less water heater that is suppose to still be under warranty.Unfortunately the company shut down and parts are no longer available.

The issue i'm having is no hot water or heat. Well, I have hot water SOMETIMES.

If I pressure up the system It will hold pressure while the hot water is running. I can have a shower, run laundry or the dishwasher, and I haveplenty of hot water. Once I shut off the taps, the system slowly loses pressure and drops to zero and throws an error code.

This system has a built in expansion vessel that doesn't seem to be building pressure. Maybe a few PSI after the system has been running.

What should the internal expansion tank be running at/holding at PSI wise?

Everything ignites fine, the pumps seem to be running fine and I cant find any leaks.

I have told I need a brand new heater by some"unreliable" sources. Looking for some good advice.

Thanks so much guys.”
 
I have always done what instructions say and that’s 2 psi below incoming pressure. This info is in the instructions for any expansion tank on shelf. But you have to determine the resting pressure of that zone first. You have to pretend or physically remove tank from system. Any water weight will give false reading at valve on expansion then slowly bleed back to eaqualize
 
Do you know who installed the system?
How old is the system?
Do you know if it ever worked properly from day one?

EDIT: I see many of those units were recalled back around 2014. Don't know when they went out of business.
No owners manual?
How about complete model name/number to try to find something on the WEB?
If the problem is in the controls, you'll have to try to get someone familiar with the system. Easier said then done.
 
Last edited:
In the meantime...

For the purpose of discussion...

There are 4 vertical water pipes entering the bottom of the unit.

I'll refer to them as numbers 1 thru 4 with #1 being on the far left.

#1 & #4 are the heating system lines.

#1 has a pressure gauge that appears to be reading(in the green zone) at about 26 psi. It also has a red hose that comes from the furnace. Just above that line, within the box appears to be a Grundfos circulator. I suspect, if you look closely, this line connects to what I assume to be the expansion tank just above it. If this is true then we can say this is the expansion tank for the heating loop, which should have no impact on the domestic hot water system.

Line #2 is the cold domestic water line, which feeds both the tankless unit as well as line #4(heating system loop), thru a backflow preventer and PRV with integral pressure gauge. Although I can't read it, I would think this gauge would be reading the same static pressure as the gauge on line #1, being on the same loop.

Line #4 shows a red hose that I'm guessing runs back to the furnace. However, there's a vertical white line that appears to have a red hose attached to it also. I can't see what's happing there. Is there a tee connection there, or what? And where does that white hose go when it drops down?

Also what's troubling me is that #3 line which should be the hot domestic water coming out of the unit. I can't see what it is doing behind that backflow preventer. It almost looks like that horizontal cold water line could be connected to it.???

How exactly do you, "pressure up the system..."?

And when you say, "It will hold pressure while the hot water is running. .....Once I shut off the taps, the system slowly loses pressure and drops to zero and throws an error code." Are you looking at the units electronic controls/readout???
 
I know that if a prv has gone bad, it will show the symptoms you are describing, (strong pressure at first then no pressure at all) you can check it by putting a guage on it and running water on the tub )IT SHOULD NOT DROP more then 5 psi if so try replacing the prv
 
I know that if a prv has gone bad, it will show the symptoms you are describing, (strong pressure at first then no pressure at all) you can check it by putting a gauge on it and running water on the tub )IT SHOULD NOT DROP more then 5 psi if so try replacing the prv
He said, "Once I shut off the taps, the system slowly loses pressure and drops to zero and throws an error code.
At this point we don't know what pressure he's referring to. In fact, he may not know what pressure it is referring to.;)
 
Thanks so much. I had one person tell me 15-20 psi. Does that sound correct?

Ill have to buy a gauge.

I would love to be able to contact the manufacturer but they went out of business and completely shut their doors and all support. Now i'm stuck with a problem that only the kind internet folks might be able to help with.

Most plumbers i've talked to don't have a clue unfortunately and just quote me 5-6k for a new one right away.
You should try to find if the company had authorized service reps. I other words, a person familiar with the system, that can trouble shoot it.

BTW...What was the error code? I've been doing a little research and although I can't find this specific unit I have found that the error codes are pretty much the same for most manufacturers.
 
In the meantime...

For the purpose of discussion...

There are 4 vertical water pipes entering the bottom of the unit.

I'll refer to them as numbers 1 thru 4 with #1 being on the far left.

#1 & #4 are the heating system lines.

#1 has a pressure gauge that appears to be reading(in the green zone) at about 26 psi. It also has a red hose that comes from the furnace. Just above that line, within the box appears to be a Grundfos circulator. I suspect, if you look closely, this line connects to what I assume to be the expansion tank just above it. If this is true then we can say this is the expansion tank for the heating loop, which should have no impact on the domestic hot water system.

Line #2 is the cold domestic water line, which feeds both the tankless unit as well as line #4(heating system loop), thru a backflow preventer and PRV with integral pressure gauge. Although I can't read it, I would think this gauge would be reading the same static pressure as the gauge on line #1, being on the same loop.

Line #4 shows a red hose that I'm guessing runs back to the furnace. However, there's a vertical white line that appears to have a red hose attached to it also. I can't see what's happing there. Is there a tee connection there, or what? And where does that white hose go when it drops down?

Also what's troubling me is that #3 line which should be the hot domestic water coming out of the unit. I can't see what it is doing behind that backflow preventer. It almost looks like that horizontal cold water line could be connected to it.???

How exactly do you, "pressure up the system..."?

And when you say, "It will hold pressure while the hot water is running. .....Once I shut off the taps, the system slowly loses pressure and drops to zero and throws an error code." Are you looking at the units electronic controls/readout???

Great news! We managed to fix the unit. for now.

Sorry for the late reply. Its people like you who make the internet a better place! very knowledgeable. Thanks so much. To answer your questions!

When I said I Pressure up the system, there is a little black valve above (line 2) you open that up and it pressures up the system to desired PSI then I close it.

Behind the back flow preventer is a mixing valve.

The error code was a"A6"


Now, I had a plumber come in and basically tell me everything in this unit was screwed. from the expansion tank to the pump, ect! he quoted me 6k for a new unit and said that'she only option. It certainly surprised me how little knowledge most plumbers have on these systems. I talked to quite a few plumbers.

All we did was replace the PRV valve with a new WATTS valve and plumbed in a inline gauge after the prv valve to get an acurate reading on the system. It seems to be holding around 15 psi and spikes up to about 20 when the hot water and heat are running

For now everything is good. i'm still very concerned for future problems as nobody seems to know a thing in this city. im grateful for these forums and everyone's help!

this leads me to my next question. How would a guy properly descale this unit?
 
You should try to find if the company had authorized service reps. I other words, a person familiar with the system, that can trouble shoot it.

BTW...What was the error code? I've been doing a little research and although I can't find this specific unit I have found that the error codes are pretty much the same for most manufacturers.



From what I can tell there is only one company in the city who still has parts for this unit and thats the only company who can access parts to this unit as well. When the company who makes the heaters shut down they gave all the remaining parts to one company and this is the company who tried to rip me off for 6k.

The unit is a Coaire COBWH -099Z

I cant find any info online
 
Well great to hear the good news!
I laughed out loud when I read your comment regarding the parts company was the same company that wanted to rip you off.
It is a complicated system and I wouldn't expect the average plumber to know all the ins and outs.
Well the error code doesn't correspond to any of the ones I came across on some YouTube videos. I'd take a long shot in the dark and say the pressure was too high and shutting it down. :D
Thanks for clearing up the mystery on why that cold water line looked like it was connected to the hot water line. I should have known it was a tempering valve. Particularly since I just replaced my tempering valve a few days ago, on an oil burner fired heating boiler. Never dawned on me that those systems used them.
I'm not very knowledgeable as far as hands on plumbing experience. I dabbled in plumbing engineering and like puzzles and researching. They say learning new things everyday wards off dementia.
Good luck with your tankless!
 
Well great to hear the good news!
I laughed out loud when I read your comment regarding the parts company was the same company that wanted to rip you off.
It is a complicated system and I wouldn't expect the average plumber to know all the ins and outs.
Well the error code doesn't correspond to any of the ones I came across on some YouTube videos. I'd take a long shot in the dark and say the pressure was too high and shutting it down. :D
Thanks for clearing up the mystery on why that cold water line looked like it was connected to the hot water line. I should have known it was a tempering valve. Particularly since I just replaced my tempering valve a few days ago, on an oil burner fired heating boiler. Never dawned on me that those systems used them.
I'm not very knowledgeable as far as hands on plumbing experience. I dabbled in plumbing engineering and like puzzles and researching. They say learning new things everyday wards off dementia.
Good luck with your tankless!


Thanks! diehard. I knew NOTHING about plumbing before a week ago. I’m a mechanic so I pick up quickly but this stuff can be complicated, especially when the plumbers don’t even know how they work. Haha!!

Keeping the brain active is key!

Thanks for all the help.

On a side note.

If anybody knows the proper way to descale these things please let me know!
 
Thanks! diehard. I knew NOTHING about plumbing before a week ago. I’m a mechanic so I pick up quickly but this stuff can be complicated, especially when the plumbers don’t even know how they work. Haha!!

Keeping the brain active is key!

Thanks for all the help.

On a side note.

If anybody knows the proper way to descale these things please let me know!
Oh yeah, I forgot about that. Others may know best but I did notice a lot of videos addressing that subject. I didn't watch them though. YouTube is a valuable resource.
 
Do you have this valve setup at the very body of your unit? I can't tell by the picture. If you do you can get biodegradable cleaner
to pump through the unit and clean it out. There's lots of videos on how to do this.Descaling valves.jpg
 

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