Top of tank to bottom of tank temps

[Wildfire]

Hello. What is a normal temperature difference from the top of tank to bottom? My solar feeds at bottom with cold water, and boiler backup is in middle, and hot water comes off top. On the nice sunny days, my Resol controller has been shutting down because the collector temp is over 200f degrees. The bottom of tank is around 130f and top is only at around 110f, so my boiler ends up coming on after noon time every day. Kinda pointless. Also the installer didn't setup the boiler in the Resol. We just have a aqua stat in the middle turning the boiler on.

[J.P.M.]

Hello. What is a normal temperature difference from the top of tank to bottom? My solar feeds at bottom with cold water, and boiler backup is in middle, and hot water comes off top. On the nice sunny days, my Resol controller has been shutting down because the collector temp is over 200f degrees. The bottom of tank is around 130f and top is only at around 110f, so my boiler ends up coming on after noon time every day. Kinda pointless. Also the installer didn't setup the boiler in the Resol. We just have a aqua stat in the middle turning the boiler on.

Something is amiss - as in things are not flowing much. I'd call for service. Since the top of a tank is usually warmer than the bottom, and you describe the reverse.

I'm guessing this is a system where the domestic H2O circulates through the collectors without a heat exchanger loop.

If so, the degree of water stratification in a DHW tank depends on many variables. When operating at a small flowrate the stratification can be VERY approx. 5-10 deg. F., more or less, and controlled by lots of variables. I run about 1.7 GPM in a single loop system through 2 X 32 ft^2 panels in series and 3/4" connecting plumbing to an 80 gal tank. The tank stratification is about nil, with the collectors running up to about 13-14 deg. F warmer than the tank under a full mid day sun in April.

[peakbagger]

Sounds like you have a bad sensor of maybe a circulator is toast.

[Wildfire]

The solar loop is not circulating dhw, it is glycol. And the boiler loop is closed that is on the top. Circulator for the solar loop works because it brings the bottom of the tank temp up.

[LucMan]

Not possible, hot water rises to the top. You have a defective sensor (s) or controller. Ohm out yor sensors at a known temperature and compare to the chart in the manual.
Or the sensors are reversed.
If your collector temp is 200 degrees your pump should be runnining to tranfer the available energy into the tank. The high limit should be set at 150-160 depending on what type of storage tank you have.