Qick plumbing question

[evesdad]

if you have got two motorised valves its a fully pumped system. Each valve actuator has an end switch which provides power for the pump and boiler (usually the orange wire). These switches sometimes stick, so when the valve body springs closed (the whirring noise you heard) the pump and boiler still run but there water has nowhere to circulate. The boiler actually boils which is the resulting banging noise you hear!