Hot water to FWA system (similar to car heater) - "Radiator" cold - no heat to house.

Riick

My house heater is a Peerless Gas Boiler to FWA system similar to an automobile's heating system. The boiler and A/C system were new in 2000. In 2020 the circulator get stuck; wacked it and it started up, but, following summer, installed new Taco 007e.
Currently: No heat. Boiler fires up, circulator shows amber LED indicating it's running normally, but there's no hot water getting to the "radiator" in the air handler.
Opened the air-release valve at top of radiator, and got 1/2 second of air, then water.
So... I think the possibilities are (a) the circulator is lying to me, or (b) there's something clogging the 3/4" copper leading from (or away) from the radiator, or, (c) the radiator itself is clogged up, or (d) the system is somehow air-bound {but I can't figure how that could be happening}
Any help in diagnosing what's going on, and, if it's a clog, how to get rid of it, most appreciated!
Thanks in Advance.
//

Jamie Hall

The pump lights may say it's running -- but is it? Does the pipe beyond it get warm or hot?

EBEBRATT-Ed

Go to the boiler and look for the pressure /temperature gauge.

The pressure should be 12-15psi. If the pressure is low you will not get heat. Where is you coil (radiator ) located??

Do you have more than one zone? Or is that one coil the only zone? Do you get domestic hot water off the boiler?

Post some pictures of the boiler and air handler if you can.

What you have is known as a "Hydro Air " system. Nothing wrong with it.

Riick

Nope, one pipe from boiler to circulator hot, no heat from return pipe. No vibration from the circulator pump whatsoever. System is heating only, no zones, there's a separate 40gal H/W heater. I'll post some pix.

hot_rod

There could be an air lock anywhere in the piping to the radiator. Do you have a purge valve on that circuit?

Riick

Yes, there's an air-release valve plumbed to the top of the radiator. Have already opened it, to cure possible air-lock, but got just a little air, then water.

Jamie Hall

Riick said:

Nope, one pipe from boiler to circulator hot, no heat from return pipe. No vibration from the circulator pump whatsoever.

How about beyond the circulator?

Riick

OK.. Drained the entire system; there was a LOT of water in the upper radiator section, 3-4 gallons out of maybe 7 gallons total? Refilled, and found that wide-opening the air-release valve on radiator splashed water all over the place, BUT, just cracking the valve gave me a hissing amount of air, and no water. It took a few minutes until I got consistent water at that valve, and with that, *finally* water began to be warm on pipe leg down to the boiler.
When I installed the new circulator, which BTW, now hums & vibrates a bit, I set up the direction of flow to fill radiator from the bottom; appears I need to reverse that so it fills from the top? How can a sealed system like this one ((there are no visible leaks anywhere)) get enough air to airlock it??
In any event, looks like I've got heat again, now, how to avoid this problem in the future

Jamie Hall

First, there is a small amount of air dissolved in the makeup water. As that water is heated, the air comes out of solution and happily collects at high points, unless it is swept away and removed with an air scoop or microbubble separator or somesuch.

Second, and rare if the pressures and piping are all correct, is that there may be locations in the system where the actual pressure when operating is less than atmospheric, and air can actually be sucked in. Note that these locations may not leak otherwise -- leaks can be one way, particularly if they involve a seal.

So the next thing to do is make sure you do, in fact, have an air separator on your system. The second thing to do is to look at the piping. If your circulator is pumping towards the expansion tank, it may well have very low pressures when running on the intake side. The pump should always be located so that it pumps away from the expansion tank, and there should be nothing except some pipe and usually the makeup water connection in between the tank and the pump.

hot_rod

It sounds like a piece of rust or crud is stuck in the circulator impeller if it vibrates or makes noise.
Hopefully you have isolation valves so you can pull the motor head off and inspect.

Rev the pump to the highest speed to help with rogue air problems, it is often enough to move bubbles along.