When this high efficiency hydronic heat and DHW-coil boiler system was initially installed, the domestic hot water would become suddenly ice cold for a few seconds while taking a shower. The boiler was cycling off because of the heat exchanger temperature. A stainless-steel insulated 20 gallon tank was added between the boiler and the domestic hot water line to temper the cold pulses. Ah, bliss. And the teens loved the infinite hot showers. Of course, every night the water in the tank with cool off and we would have to run hot water in order to heat it up again.
A hydronic circulator pump was connected to the stainless – steel tank with a rising-plug or piston type check valve between the pump and domestic cold water supply line to the boiler. The pump was controlled by an aquastat which was sensing the temperature in the insulated stainless – steel tank. This worked very well for many years. Then the check valve failed.
When the valve was replaced, the carbon steel pin which acted as a guide for the piston was found to have corroded away. This obviously was a poor design choice because it was a very small amount of wet carbin-steel in electrical contact with a very large amount of brass. The same thing happened with the replacement check valve.
Discussing this with a manufacturer of the valve, we found that this type of valve was not designed for potable water (lead eek) and therefore it should not have been installed in the first place. A swing check valve was installed in its place because it was impossible to find a potable water rated rising plug check valve.
After that, the swing check valve would chatter constantly whenever hot water was being used. In hopes of improving the installation, the check valve was moved further downstream from the pump to avoid turbulence. That did not help.
A normally closed solenoid valve (controlled by the same aquastat as the circulating pump) was installed in the same pipe. The chattering stopped as long as the pump was not running. However, as you can imagine, when the stainless – steel tank got cold and hot water was being used the valve would chatter.
Subsequently, the swing check valve was replaced with a spring-loaded disc check valve. The chattering was somewhat less noticeable but still present.
Thank you for reading this far.
Can you recommend a solution to the chattering?
sketch illustrates the schematic layout of piping. Controls, and safeties are not shown.