Hydronic floor system keeps over pressurizing itself

[Shibby021]

Last night I fired up my heat on, its a slab radiant floor heating with Hydrosmart 120 tankless boiler heating the system up.

I set the system pressure to 18psi, but it kept pushing over 30psi, I bleed the excess pressure out few times over the night before I went to bed. I just woke up, the system is off but zero pressure....

This is pretty much new system First ran it last January so not a year old yet. Last season it ran great, just that every time it stops, it loses few psi, then when fired up again, it gets some of its pressure back but never back near to 18psi, after few cycles it eventually ended up at zero psi. I never did anything to it since.

Couple days ago, I decided to run each line for 2 min each in a bucket to see if any bubbles came out. Nothing did so I pressurized the system to 18psi and left it alone and closed both manifolds. Next day It dropped to 10 psi. This was with the air separator cap open 1/8 turn to 1/4 turn. I decided to close the cap, and next day it stayed at 10psi.

I am guessing I have some issue with the air separator or perhaps the pressure tank as the pressure tank is screwed to the bottom of the air separator.

*** edit 1 add photo of my system that I made myself.

 

[Reach4]

The air precharge pressure should be the same as the cold system pressure. Eighteen psi is on the high side. https://terrylove.com/forums/index.php?threads/how-much-psi-for-my-boiler.55106/

Close the valve to the automatic refill valve. If the over-pressurizing still happens, your thermal expansion tank is too small.

This is based on comments from others, because I have no relevant experience.

 

[Sponsor]

 

[John Gayewski]

Over pressure is usually the expansion tank. Then check the fill valve. Reach is right, 12 psi is normal fill pressure.

Unscrew the air fill cap on the expansion tank if there's any water in there it's bad. If no water is present seperate it from the system and check the charge, it should be 12 or so. Your expansion tank looks big enough for this system.

 

[Shibby021]

I checked tank air pressure, it was at 35psi, I drained it below the tank fitting but did not take the tank off, and bleed the air to 12psi. Will that work or do I need to take the tank off and pour the water out and check the air pressure?

It's running now at 130f as of 3:45pm cst.

When it was turned on, I set it to 12psi on the hot side, and that would make the cold side 16psi.

It's 4pm, 15 mins 14psi/19psi

It used to reach around 30 psi within 15 mins of runtime. SO it's a improvement so far.

 

[Shibby021]

4:37pm checked and pressure was still holding 14/19 so I turned off the system, came back at 4:55pm to find out its at 0psi.

I am supposed to run it with the air separator bleed cap slightly open or is it supposed to be closed?

I turned the system back on and after 20 minutes it is 14/19 again, so I turned it off and closed the bleed cap on the air separator, 20 mins later I checked again and its down to zero again.

 

[John Gayewski]

You have to take the tank off. Set the tank at 12. Then reinstall the tank. Since you don't have a valve before the track is a pain. It doesn't even look like you have room for a valve.

The idea is the tank can take the extra water created as it gets hot and expands.

 

[Fitter30]

Top pump the valve to the left between the two back to back tees open it 100%. With valve closed there is no hydraulic separation. The other possible problem is the length of pipe entering minimum 8 pipe diameters leaving 4 the tees and hopefully the valve between the tees is full port. Lower fill pressure to 10-12 lbs is more than enough water. 10 lbs = 23' with all pumps off water under 100°. Readjust ex tank pressure to fill pressure. Do see where the.make up comes in.