Pump Control for DHW loop

[McKraut]

When you use a plate exchanger to heat your DHW, the boiler is supposed to be supplying the heat. How do you prevent the reverse from happening if the boiler temp falls below the HWH tank? If the HWH temperature is set for 160* and the boiler is down to 120*, doesn't the HWH then become the heat source for the boiler (until it is re-fired)? Is there a way to shut down the circulator on the zone or on the HWH to stop this?
Thank you,
Bob

 

[salecker]

Get an aquastate in line to control it.

 

[gthomas785]

2 aquastats wired in series, one calls for heat when the DHW tank cools off and the other breaks the call for heat if the boiler outlet temp is too low.

 

[McKraut]

2 aquastats wired in series, one calls for heat when the DHW tank cools off and the other breaks the call for heat if the boiler outlet temp is too low.

Can you give me a specific aquastat model #/manufacturer that would work for me?
Thank you,

Bob

 

[gthomas785]

Well I don't know how your system is piped but here's a pretty generic strap on one that can be used as a high or low limit

https://www.supplyhouse.com/Resideo-L6006C1018-High-or-Low-Limit-Circulator-Strap-On-Aquastat-65-200-DegreeF-range-5-30-DegreeF-Adj-Differential

 

[gthomas785]

I assume you're already cycling the circulator off some kind of thermostatic control on the DHW tank? In that case you just need the one additional sensor at the boiler

 

[McKraut]

Yes, I am. I was on the same website checking out their aquastats. Thank you for the information. This will be a big help.

Bob