Thermal instability (geothermal wells applied)

Good afternoon everyone,

I really need help calibrating my model. Everytime I start my simulation it happens that, after a certain period of time, temperature on a certain point on the border start increasing, reaching anomalous temperatures over the years.
My model is a the city scale, it is an unconfined acquifer with a fluid flux from North-Ovest to East and some geothermal wells (for which I have already re-checked all the thermal and hydraulic time-series thanks to a simulation in a smaller model involving the same conditions).
Why does it happens? Someone can help me?
I have tried to simplify it removing building and BC of the third kinds, just leaving the soil thermal properties and a costant temperature (BC of the first kind) on the north and south and West borders.

I am really desperate.
Thanks to those who will try to help me.

Hi Maria,
The problem you are describing may be related to the combination of flow and heat transport boundary conditions. Can you check whether the rate budget means sense (or fulfill your expectations) in terms of the Fluid-Flux boundary? FEFLOW uses a backward approach for the budget calculation, i.e. it uses the resulting primary solution (head, concentration and temperature) to compute the fluid, mass and heat rate budgets. That means that sometimes what you set (e.g. Fluid-Flux BC) is not always what you get. Finer the mesh discretization is, better these two numbers are approaching to each other.

Cheers
Carlos