I have hot water heat. My pipes make a single banging sound when the thermostat shuts off in each zone. Only when they shut off. I upgraded the system with a new expansion tank, direct pump, and air scrubber. The boiler's operating pressure is 30 psi and water feed to the boiler is 12 psi. It is an American Standard boiler.

The boiler pressure seems to be set at that higher end of the setting hear For now I would set the automatic fill at 8 or 9 lbs and when the boiler cooled down release some pressure out of the pressure relief valve and reset the cold starting at 9lbs and see how that does. The main reason any boiler is set st higher psi on the system is because of Lift to get to top rads. And overcome gravity fighting that. Try a bit lower pressure and get back Its worth a try and easy to do.
Before you re adjust re bleed all baseboard/rads to make sure its not air hammer in the system that a zone valve could cause. The banging is inductive to air in the system
I'm curios what was wrong with the old tank and how was the new sized and who did that? Also the Direct pump explain that more please?
I'm leaning to air in lines and when the Zone valve completely shuts off that air in the system can easily go thump. Just like shutting of a faucet with air in line or at high pressure in a line.

Signed 21 Boat

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The boiler pressure seems to be set at that higher end of the setting hear For now I would set the automatic fill at 8 or 9 lbs and when the boiler cooled down release some pressure out of the pressure relief valve and reset the cold starting at 9lbs and see how that does. The main reason any boiler is set st higher psi on the system is because of Lift to get to top rads. and overcome gravity fighting that. Try a bit lower pressure and get back Its worth a try and easy to do.
Before you re adjust re bleed all baseboard/rads to make sure its not air hammer in the system that a zone valve could cause. The banging is inductive to air in the system
I'm curios what was wrong with the old tank and how was the new sized and who did that? Also the Direct pump explain that more please?
I'm leaning to air in lines and when the Zone valve completely shuts off that air in the system can easily go thump. Just like shutting of a faucet with air in line or at high pressure in a line.

Signed 21 Boat

If I Helped To Answer Your Question Please Rate My Answer

First, I made a misstake. The boiler pressure is 17 psi at 190 F. The pump is a Wilo Star-S set to #3. The air scrubber is a Spirovent. The previous tank was an old steel air tank. After describing my system to the plumbing supply. They suggested an Amtrol Model 30. I will bleed the zone again. Could the pump be set too high. The counter guy said to leave the pump at 3. I'll have to look at the pump instructions again. 1 is 41, 2 is 60, 3 is 80.