Suction on hydronic radiator bleed valve, is my pressure reducing valve too low?

Jells

I was servicing a 3rd floor hydronic system with cast iron baseboard and the boiler in the basement. But when I went to bleed a rad it was sucking not blowing! ****? The circulator seems to be working, I opened the drain and fill arm on the pressure reducing valve in the basement and flushed some water through the loop, but still get vacuum on the bleed.The system is 16 years old and don't recall this, though I'm not great with regular maintenance like bleeding, in this case the tenant said the rad in the room at the end of the loop wasn't heating well. The rad is about 28' above the boiler. This gauge appears to say around 13 psi, which at ~1/2lb per ft seems like it might not be enough pressure to get there. The other boilers for the lower floors read same pressure. What am I missing? Is the pressure reducing valve failing?

STEVEusaPA

First I’d confirm pressure with another gauge. You probably need about 18 psi.
Make sure you’re filling with the circulator off.
Also, if you’re not pumping away from the expansion tank you could be going negative at the top of the system.
https://youtu.be/tZRuqiQkukE

hot_rod

A positive 5 psi at the highest point, ideally, so 28 X.433= 12.1 psi + 5= 17 psi.
The expansion tank location or connection needs to be on the suction side of the circulator.
Also when you raise fill pressure, the expansion tank needs to be isolated and then precharge set at 16- 17 psi for that fill pressure.

dopey27177

When filling or bleeding air from any water heating system the circulating pump needs to be off otherwise you may suck air into the system.

Hot Rods formula is perfect to determine the pressure in the water heating system.

Jacob Myron

EBEBRATT-Ed

I have run into this before.

I would bet that the circulator is pumping towards the expansion tank

Jells

EBEBRATT-Ed said:

I have run into this before.

I would bet that the circulator is pumping towards the expansion tank

I don't think so, all appears correct. Here's 2 of the 3. I'm going to try and increase pressure, I have another gauge I can put on. I've never had to mess with the pressure reducers, I didn't even realize that they are adjustable. Are all of them???

hot_rod

correct on the pump/ tank relationship, assuming that circulator is pumping into the boiler return? Should be able to adjust any fill valve. But sometimes they don't work real well if they have been sitting for years, it may leak through and over-pressurize, keep an eye on a good pressure gauge.

Buy a pressure gauge with a hose connection, plumbing supply or box stores, and screw it onto that valve below the circulator to get an accurate read, move it to other boilers.
Or build your own with a nice gauge and hose to 1/4 fip adapter, like this

Jells

I already have one with a hose bib adapter, but it's a little higher range than that one.

hot_rod

0-30 or 0-60psi will work, then gauge on the boiler is too coarse and hard to see a few psi differences.