Indirect Storage tank inputs and outputs used with Tankless FlowMax90 boiler issue / question

videopete · Jan 25, 2023

I have an indirect storage tank being used in my home heating system (hot water is generated from a tankless unit and stored in this tank to be used by domestic water).
The tank is a GIANT 142ETE-9G7M.
It has two inlets on top. One inlet is connected to my furnace (hydronic air handler) that uses hot water coils (always hot) and the 2nd inlet has my House COLD water coming into a thermostatic mixing valve (COLD SIDE), and the HOT side of this valve comes from the Storage tank (2nd inlet), the MIX outlet of the mixing valve goes to my domestic hot water needs (faucets etc) I've attached some crude pictures (sorry) for reference.
This 2nd inlet is sometimes HOT (when my faucet is on I'm assuming hot water is coming out from here???) and then freezing cold (when no faucets are in use and cold water coming in from source??)
Can this mixing valve let water pass through from the COLD side to the HOT side (this is the only way I see water coming into the tank)??

My end game is to completely REMOVE this mixing valve as it's hit and miss with the water temp and simply get cold water into the tank from that inlet but that means I would have to use the 2nd inlet as HOT both incoming and outgoing - is this possible with a storage tank (one inlet with water going both ways ??)

I am not a plumber by any means and ANY help would be greatly appreciated.
My local plumbers (two that I've called so far) have no idea ?? which baffles me...so here I am asking on a forum hoping for some clarification.

videopete · Jan 30, 2023

Anyone with some advice ?

Geofd · Jan 30, 2023

Have you thought about changing the cartridge.in the mixing valve????

dmmsr · Feb 3, 2023

So if you re-pipe, you should pipe domestic cold into cold side of tank and cold side of tankless, install hot coming from tankless to the drain valve at the bottom with a tee to reinstall the drain valve. Put a check valve on cold side. Also need to install an expansion tank. install a recirc pump on cold water.
Then pipe hot side to domestic hot water. Use thermostat to turn recirc pump on and off.

videopete · Feb 6, 2023

dmmsr said:
So if you re-pipe, you should pipe domestic cold into cold side of tank and cold side of tankless, install hot coming from tankless to the drain valve at the bottom with a tee to reinstall the drain valve. Put a check valve on cold side. Also need to install an expansion tank. install a recirc pump on cold water.
Then pipe hot side to domestic hot water. Use thermostat to turn recirc pump on and off.

Thanks for the reply. I would prefer to keep it as simple as possible with only a few changes if possible (ie. not moving recirc pump, etc). Can I not move that House cold IN to simply go into the cold side of the tankless (it would be the same existing line that is on the recirculator pump coming out of the tank going into the tankless cold in). So the storage tank would simply be left with one HOT coming out for domestic (with no mixing valve) and one HOT going in (which is the current return from the air handler ). It's like your photo (cold going into the recirc line) except my recirc pump is at the bottom of that tank where the drain valve is and not using one of the top two outlets.
Also, my HOT OUT from the tankless goes into the furnace side where a valve/switch decides if a call for heat is ON, hot water goes to the furnace, if the call for heat is off, water gets redirected back into the storage tank from the top.