Heat loop question

When you make this statement: "I have a low hot water loop on my steam boiler."

This could be an open system where that copper pipe has less than 3 PSI static pressure using the water directly from the steam boiler that actually produces the steam. .

When you add the last 4 words: "I have a low hot water loop on my steam boiler from a heat coil"

This could mean that it is a closed system where there is a tankless coil inside the steam boiler and the static pressure inside that copper pipe and DirtMag is 10 PSI or more. That would mean you need a circulator, water feed, expansion tank, a pressure relief valve, and perhaps an air scoop.

I also see a white expansion tank, which is indicative of a water heater open system. With these three different possible heating system designs, I have to ask: why is your picture only showing the DirtMag?

Your limited steam boiler photo reminds me of the person who posted this photo on an automobile help site

What Am I missing here? I was told that I can fill my tire with air pressure using this small valve in the tire rim. I have been adding air from my compressor for over two hours and that tire is not getting filled.

When asked to post a photo from a little further back, the answer was obvious

I was wondering if you might have a picture of that DirtMag that also includes the boiler, circulator, and expansion tank, along with more angles so we can see the entire system. That will help us determine where the dirt might be coming from. Also, what kind of radiators are on the copper "low hot water loop"?

We may even be able to tell you how to find if you have Ghost Flow as @Jamie Hall mentioned.

That is a nice job. …and you actually have two zones of hot water radiators if I am not mistaken. One is an open system using steam boiler water (the lower zone) and the other is a closed system using the tankless coil going above the boiler. Which system is the Dirt Mag query about? It appears to be on the open system. behind the boiler as viewed from this photo:

As long as the radiators are all below the water line on the low zone in the open system, you should not get gravity or ghost flow. That usually happens with radiators that are above the boiler, since hot water is lighter than cooler water.

It is unlikely that 180° boiler water is leaving the boiler and flowing down to lower radiators when the pump is off. You may be experiencing some other problem, or perhaps not all your radiators are below the water line on that open loop.

A flow check may not solve your problem and could only add to the pump’s tendency to cavitate when the boiler is steaming for the main zone.

Didn't we just see this boiler?