Constant issue with air getting into oil heat system

PIngerick

We have an oil furnace that also provides household hot water. The system is a Weil McClain system installed in 2018. Has two zones for a ranch home. Since we bought the house in 2020 we’ve had issues. One of the zone pumps keeps burning up and has been replaced twice but still there is air in the system which causes gurgling and eventually the heat stops working. Seems like air keeps getting into the system but the HVAC techs can’t seem to fix it. Had it serviced at least 9 times since late 2020. Any insights are appreciated!
—Pat

Big Ed_4

Does the heating pipes run into a slab floor ?

PIngerick

No the boiler is in an unfinished basement 
Correction. Zone one which is the one the serves the majority of the heat and seems to have the air problem is not under a slab. However zone two heats a large family room that is on a slab. So I’m guessing those pipes are under a slab floor. 

Big Ed_4

post photos of system ....

PIngerick

As I mentioned zone one is the problem. Zone two seems to work fine. Zone two is on a slab. Zone one is over the basement 

SuperTech

I've seen constant problems with boilers that have the copper pipes run into slab. I would isolate the zones that go into the slab and see if it loses pressure. I was recently on a call that had the same problem with air getting into the upstairs zone. The 3/4" copper pipes had turned green where they went into the slab. When isolated the pressure on the boiler would drop to zero in about ten minutes. Another indicator of this problem was the boiler water was extremely brown and rusty when drained from the constant introduction of fresh oxygen rich water rusting out the boiler. 

Jon_blaney

I also think you have a leak in the slab zone. The auto fill is dumping air laden water into the system. That fill water is possibly effecting the air separator's function because of the fills location. An infrared camera could be used to find the hotspots. Copper in a slab, no if but when it will leak.

HVACNUT

Certainly seems like a slab leak. 
Also needs a Firomatic valve at the burner.

STEVEusaPA

@Jon_blaney there's nothing wrong with the fill/air separator/expansion tank/circulators. Actually it's piped correctly.
Slab leak or not, it would only kill the circulator (air) if the air separator wasn't working. And not 9 times in 1.5 years.
Has anyone autopsied the circulators? Maybe you need mag separation.

PIngerick

Thanks for the suggestions. How would I go about checking the circulators and a possible slab leak?

Jamie Hall

To check for a leak is really pretty simple -- in slightly warmer weather. Start with the system cold and note the pressure on the gauge. Close the valve on the line from your domestic water to the autofeeder. Watch the pressure in the system -- it should stay constant. If it drops over a few hours, you have a leak. To find out which zone, bring the pressure back up again and this time close not only the valve to the autofeeder, but the isolating valves (I hope they're there...) for one of the zones. If the pressure drops, it's in the zone which is still open. If it doesn't, it's in the zone you isolated.

Jon_blaney

check for a leak by turning off all water users, sink, showers, etc. Stand and watch the water meter and see if you have any flow. Should be zero. Have both zones calling for heat.

PIngerick

Is there an easy way to purge air from the system?