Oil Backup Struggles to Xfer Heat to Tank

[Rory]

I'm on my third winter with my Tarm Solo 30, using 670 gallons of unpressurized storage which also houses my DHW coil. I have my old oil furnace tied in as a backup, using a Johnson setpoint controller which I turn down in the summer and up a bit in the winter. The furnace occasionally comes on, but I typically have another fire going before I expect much out of it. Yesterday was the first time I've left overnight in the winter with the expectation of the oil taking over, so I bumped the setpoint up to 160 and left a full fire going in the Tarm. Today, although the house was warm, my tank was only 126 where the Johnson was reading while the furnace was stalled with 180 degree water in the jacket. It doesn't seem as though it's able to transfer the heat into the tank quickly enough. The oil furnace is close to my tank, while the Tarm is about 50 degrees away. I'm wondering if the pump at the Tarm should kick in with the oil furnace circulator, or if the resistance of the water to the Tarm should allow flow from the oil furnace through the heat exchanger in an efficient manner.

Please don't ask me to print a diagram of the setup, as I don't know where it is.

Any thoughts?

 

[RobC]

Is it possible that your oil boiler supply water is going directly to zones when zones call for heat ? Sounds like your expecting the OB to heat storage like the Tarm does, including the DHW which is potentially problematic with the way thing are working now.
One way to check is to let Tarm go out tomorrow and when the oil comes on be there and see exactly what happens. Feel the pipes and see where water is going.
Does your circulator at the Tarm have a flow check valve ? That combined with the Tremovar should create enough restriction that the water won't circulate through Tarm. While on oil you don't want to circulate water through Tarm.

 

[Rory]

Well, it turns out that the relay controlling the circulator into the oil furnace was flaky. My plumber replaced the entire control unit which includes the relay on my oil furnace and everything seems to be ok now. The heat exchanger in my tank can absorb nearly all the heat my furnace will produce, giving me a longer run time until thermal shutoff, and the circ will continue the heat exchange loop after the furnace shuts off. To be clear, I now have 3 circulators in the the system - one from the Tarm to the storage tank, one to drive the heat zones, and the original pump which pulls return water into the oil furnace and now drives the tank loop as well when the oil furnace is running.

 

[NYEDGE]

Glad things are working now.
I agree with the previous posts that you don't want to heat your storage with the oil boiler, only supply heat to the zones as needed.

 

[Rory]

Glad things are working now.
I agree with the previous posts that you don't want to heat your storage with the oil boiler, only supply heat to the zones as needed.

If I took your advice I wouldn't have any domestic hot water if I didn't burn wood for whatever reason.

 

[NYEDGE]

Glad things are working now.
I agree with the previous posts that you don't want to heat your storage with the oil boiler, only supply heat to the zones as needed.

If I took your advice I wouldn't have any domestic hot water if I didn't burn wood for whatever reason.

Sorry, didn't notice your DH coil was in the storage.