Solar Thermal Heated Water From Cylinder To Shower Pump Is Too HOT During Summer

After using my shower during any hot summer day, the shower pump always attempts to start with the usual starting noise whenever we close any hot water tap. Sometimes, the sporadic noise persists for a long spell! On each occasion, the noise ceases when we open any hot water tap and close it gently. I have been advised to install a TMV to the pipe between the Hot Water Cylinder and the Shower Pump. Before doing so, I thought it would be useful to ask the community for advice from those with similar experience of the problem

Question: If your have experienced this problem, could you please advise on the solution- was it a TMV or something else?