Boiler pressure loss.

nibs

First of all HAPPY NEW YEAR.
This morning woke up to cold house, Rinnai combi shut down due to pressure loss.
Topped up the system and it ran the air remove cycle and it started up as usual.
Hydronic pex in slab, no pressure loss since installation about 6 years ago.
No visible signs of leaks, Amitrol expansion tank 5 yrs old, seems to be ok, tapped it with the back of knife, rings until the mid point thuds after that, so sounds ok.
No inslab joins for the pex.
Did have an issue a month ago and cleaned some crud out of the strainer on the return line, but has been fine since, also at that time took out the ignitor and flame sensor & cleaned then reinstalled..
Any clues, would be appreciated.

Big Ed_4

If you keep the system feed valve closed , you need to maintain the pressure in the compression tank , assuming there are no water system leaks ....

nibs

Ed it happened very suddenly, and it seemed like about a gallon of water had to be replaced, so far after about 30 hours run time the pressure is staying good. No visible leaks,

hilltown

Did the pressure on the controller match the pressure on the analog gauge.?
Have seen the boiler pressure sensor have debris at the orfice causing fluctuation in what the controller is reading vs the analog. Clean the pressure sensor out and haven’t gone back.

nibs

Happened again last night, & there is a damp spot directly under the relief valve. Took much less fill water to bring the pressure up, this time, am thinking that the expansion tank has failed and the relief valve blew, because there is no functioning expansion room, will put a catch pail under the relief valve to see if we can verify the source of the leak.

GGross

What is your cold fill pressure set to?

nibs

I fill manually and try to keep it at about 14psi but today I bring it up to 14 and it drops. looks now like the leak is at the condensate tray area, above the circ pump. Problem of course is where is the water coming from, gonna pull the condensate tray now & see what we can see.

mattmia2

What is the air pressure in the expansion tank with it removed from the system?

EBEBRATT-Ed

It probably is the expansion tank. When the pressure starts to fluctuate wildly from a hot to a cool boiler it's probably the ex tank.