New Homeowners Looking for Help: Hydronic Heating

Rosecliff

We recently bought our first home: an older, ranch on a slab with hydronic heating. The heating system worked fine though the winter, however a few days ago we stopped getting heat. The boiler was maintaining temperature, and the system was maintaining pressure, so we assumed the circulator must have seized - it was extremely hot to the touch. Earlier this morning we drained the boiler, replaced the circulator, and are now attempting to refill the boiler - without luck. We're not sure why we're unable to get the boiler to fill back up, and would appreciate any insights from the community.

After replacing the circulator, we:

1. Left the electric off.
2. Closed the boiler drain valve (red circle).
3. Opened the boiler supply valve (cyan circle).
4. Opened the bleeder key on the "first" radiator in the system.
5. Drained the water until we got only air.

We're not hearing any sounds of running water near the boiler at all. Any ideas what we could be missing?

(Also, it also turns out that the circulator was moving just fine; so not sure how else to diagnose the problem....)

hot_rod

circulators get hot like that when they are seized up, or air locked and not moving fluid. You need valves in a few critical places to force water through every pipe and radiator. Bleeder on radiators may not be enough to get air out of the piping. It looks like a water heater pressure relief valve on the 

If so the valve should be at the boiler and a 30 psi relief valve

Maybe a drawing of the boiler piping would help see if there are purge valves installed

Was the system noises before it quit? That would be an indication of air in the lines.

Rosecliff

Hot Rod-

No, no odd noises at all before the system quit. We haven't had any gurgling in the pipes since we worked all the air out when we first moved in. Agree completely that the piping is a bit messy to follow. The pressure relief valve sits between the supply valve and the boiler; we haven't touched it at all, since it seemed to maintain the correct pressure until we drained the boiler this morning.

Any suggestions on where should we look for purge valves? On the return side?

Rosecliff

We attempted a drawing of the heating system, with all of the relevant valves, etc. marked.

Jamie Hall

They didn't do you any favours at all.

First, it's a pressure reducing valve -- not pressure relief valve. But that''s minor.

You don't show the location of the circulating pump on your diagram?

To really effectively purge a heating system of air, you need to get a really good flow of water through it -- 5 gallons per minute would not be too much. However, if that is all the valves and drains you have, I'm not sure how you are going to do that.

The first thing I would do is an extension of what you have already done (I know: the definition of insanity is to do the same thing that didn't work, and expect a different outcome, but...): that is open the bleeder on each radiator in turn, making sure while you are doing it that the pressure in the system really does stay high enough that you get a good run of water out of the bleeder. Then go on to the next one... and so on. Start with the highest elevation first. Then go back to the beginning and do it all over again.

Then try the system and see if you get any better results. You might get enough of the air out that way so that the automatic air valve near the expansion tank can take care of the rest. If not, it may be that more drastic measures are needed...

HVACNUT

Any valves and drains on this pipe going away from the boiler? The supply splits right where it goes into the slab. Is the split on the return accessible? It's one zone but two loops so they need to be purged independently. 
And that's a terrible location for a circulator without isolation valves. 

Ironman

Where are you located?

hot_rod

This pic shows a T&P water heater relief in the upper corner. If it is into any boiler piping it is not the correct valve

EBEBRATT-Ed

Sounds like the prv is not feeding water

Rosecliff

Well, strangely, after bleeding the radiators again this morning, checking the screen on the pressure reducing valve (fine), and letting the system sit untouched for a number hours, we're back to working pressure and heat in the house. I suspect our system just takes that long to refill; we simply weren't being patient enough.

That being said, I'm not convinced we've actually solved the original problem. The (new) circulator is still extremely hot when it runs; and per many of your comments, sounds like there are a number of things that we should address. I think a few of our assumptions, and the schematic, need updating based on a few of the comments above. I'll revisit tomorrow with fresh eyes and provide updates. For now, going to go enjoy a warm bed.

hot_rod

The pump will run a bit warmer than the fluid it is moving. The system fluid runs through the motor, called a wet rotor circulator. Yours is also under the jacket near the burners, Check it with a temperature gun or strap on thermometer to know if it is too hot.

If it runs with valves closed it is dead-heading, a term coined by Jerry Garcia, it will be smoking😚

Ironman

There’s also a screen on the inlet of the back flow preventor that may be clogged. It shouldn’t take hours for the system to fill.