sidearm heat exchanger

I have my HW tank thermostat set at 130, just wondering if my boiler supply is below 130 as it was this morning cold night,does the sidearm action reverse where the HW tank tries to heat the supply water? If this is the case I should probably put on some sort of thermostatically controlled valve to shut off the supply if it drops too low. Any recommendations would be appreciated.

I think it could, yes. That's why I put a simple check valve in my sidearm heat return line. I'm not sure how good it works as I've kind of neglected my sidearm circuit until I get other things finished up, but last week when my storage was cold and hot water tank hot I did some checking just feeling for warmth with my hands & there didn't seem to be any heat moving through either side of the sidearm. I also have a NC zone valve plumbed into the sidearm heat supply line but it isn't wired up yet. I want to find a simple control that I can use a surface probe on my tanks with & if it drops to a certain point, it will open the zone valve circuit so the zone valve closes.

I had to install a check valve on mine, as thermosyphon action will cause you to lose that heat in water heater.

All heat exchangers work both ways. Side A to B or side B to A. Whichever is higher temp loses heat to the other side. Heat always flows from the hotter medium to the lower regardless.

This can definitely happen. I put a full bore ball valve in line with the DHW port on my sidearm to stop it. I didn't use a check valve because I was concerned about reducing flow when the boiler is operating. When I'm using my boiler for heat, I just shut off my water heater and open the valve. Not using the boiler for heat? Close the valve, turn on water heater. It has also occurred to me that I can use my water heater to keep the boiler from freezing in an emergency, but I don't expect to ever have to do that.

Is there an electric valve that will shut it off automatically?

Maple, Honeywell makes an aquastat with a remote sensing bulb. You can get one of those, put the bulb on the tank (or the supply line leaving the tank), and wire your ZV through there. The one I have has an adjustable set point, and I just dial it in where I need to. I use it for enabling my backup boiler when my storage tanks arent hot enough.

Thanks Guys I'll go to the suppliers websites and get an aqua stat to solve this issue. K

I tried the check valve method but after a couple of seasons the valve stuck open and I ended up removing it anyway. the aquastat/zone valve solution works much better.

You could probably get one from Taco. In conjunction with a snap-switch mounted on the supply line from your boiler (snap-switch = thermally activated switch ... Senasys makes + sells a broad variety), you could probably completely automate it.