I live in a condominium unit and have a thermostatic control valve in my shower. I have just been advised that it is faulty (asymptomatic to me because I don't have any problem with water temperature which has always been set at the optimal 38 degree C ). The alleged faulty valve is causing temperature fluctuations in showers on floors above and below me. How can I verify that my valve is faulty? Can I install a check valve ( what type ?) in my hot or cold water supply lines to the shower to prevent future potential crossover problems ( will happen over time arising from a faulty in the valve due to wear and tear ) affecting showers in other unit(s) on the same supply line due to a faulty valve in my shower?