Thermal store and Aga
 

Hello. We have an oil fired Aga and it is connected to our thermal store.When the water gets too hot in the thermal store the excess circulates around the radiators. This system has worked perfectly for 4 years. Suddenly the water is starting to boil in the thermal store, bubbling into the expansion tank and going out through the overflow pipe. The thermostat has been changed and the pump is working. We have checked for blockages in the water pipes.We are stumped.Does anyone have any ideas please?

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