Circulation Pump Issue

Over the past weekend when working in the shop, I noticed the circulation pump on the hydronic system would start making a whining noise. It sounded like it was starving, but if I switched the system off for a few seconds and then back on again the sound would go away for a few hours before returning. It could also be the pump itself so I did some quick research on Google to see what the problem might be.

I quickly found that these pumps like to operate under at least 15 pounds of system pressure. That pressure is normally very easy to achieve because a system like this is connected to the city water supply and you would simply open the intake valve for a few seconds to raise the pressure. Well, my system is totally closed and isolated from any external pressure source. I wanted to avoid adding another valve or opening the system up if possible, so I came up with a "backdoor" approach. It actually worked great, so I figured I'd detail it here in case I need to do again in the future.

I didn't take any pictures, but what I ended up doing was releasing all the air pressure from the expansion tank (15psi), then attaching an air nozzle quick connect to the male end of a garden hose. Once that was done, I poured just over a gallon (4 liters) of pre-mixed Anti-freeze into the hose before attaching it to the drain valve of the water tank. After that, I set the air compressor to 40psi and opened the drain valve on the tank.

I could hear the liquid and air being forced into the tank while lifting the hose above the height of the tank working from the far end of the hose towards the tank to make sure all the anti-freeze solution was forced in. The air release valve did a great job of bleeding the air without so much as leaking a drop of fluid! The whole filling process took no more than a couple of minutes and once the hose was empty, I shut off the drain valve to seal up the system again and re-pressurized the expansion tank to 20psi.

After cleaning up, I checked for leaks and then turned it back on. The air release valve continued to burp and hiss for some time as it worked out the remaining air, but the pump whine is gone and after 12 hours of run time it still sounds great.

I'll call this issue resolved for now.