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Update

Hey guys,

So I did the following:

Replaced supply and return flex lines out to TigerLoop brand lines

Changed out pump inlet brass elbow to a new 1/8"NPT M by 3/16" Flare M (not easy to find)

Changed out brass nozzle oil line from pump to nozzle

After this, I now read 0" of vacuum during prepurge and when the burner is running.

Hopefully zero inches of vacuum is a good number 😀

I did notice with the old flex line that the vacuum gauge needle would bounce when I wiggled the flex supply line - perhaps this is where the leak was.

Thanks again for all the help!

A two pipe system returns unburned fuel back to your oil tank preferably with a top fed oil delivery and return piping.

Take a picture of the boiler and post it. @EdTheHeaterMan will know if/where the aquastat is, or where to put one. At the very simplest, you could add a strap-on adjustable aquastat to the supply pipe coming out of the boiler that would cut power when the supply water temp hits the adjustable setpoint. But I would assume the boiler itself must have provision for an aquastat to be mounted on it somewhere.

Hi, That grey box that has the upside down Honeywell… could you get a photo of that, with the cover removed? 😊

Yours, Larry

@person56 said:

"One additional question is what should normal temp range be when running full load? My boiler seems to hit highs of around 220, which seems like a lot. "

Say what? You do know that water boils at 212 degrees at atmospheric pressure, right? 220 is dangerously close to becoming a steam boiler bomb. The only reason your boiler water hasn't turned to steam already is the slightly higher pressure.

So I think we found your problem, or at least one of them. Your water temperature is way too high. Your aquastat should be set for 180 max as a safety. And you can set it lower if you still get adequate heat at lower temps. The lower the max temp, the less expansion volume you need.

On the subject of expansion tank sizing, what matters more than acceptance volume is the free air volume at max acceptance. The EX-30 has only about 2 gallons of free air volume at max acceptance, while the EX-60 has 4 gallons of free air volume at roughly the same max acceptance. The doubled free air volume means the max pressure in the EX-60 will be much lower for the same acceptance.

But fix your aquastat setting.