nigeldodd

The sensor is correctly calibrated. The temperature stratification is as I have described, 40 deg C at the bottom and 90 deg C at the top. It roughly agrees with the graph that Radian has posted above.

The observation that hw tanks exhibit such stratification in temperature is very interesting. I am not sure if this thread is still live, but I will give my two Eurocents worth. My situation is slightly different. I have a Powermax gas boiler with an integrated 100 litre tank and the immersion heater is at the bottom. I have a homemade diverter with the temperature sensor also at the bottom. Recently this temperature sensor was reading 40 deg C and, alarmingly, the pressure/temperature relief valve at the top of the tank opened and hot steaming water started gushing through the tundish. When opened a hot tap, the temperature of the water was 90 deg C. The stratification effect is real and in my case a barrier to storing the maximum amount of energy from the solar pv panels in the form of hot water. I will put another temperature sensor at the top of the tank and use this to turn off the diverter. My strategy now is to dump power into the hot water at the beginning and end of the day while in the middle of the day, when the sun is at its strongest, to dump the energy into the car.