Next to our hot water tank, there is some sort of pump which comes on when either the bath or shower is turned on. I'm not sure if it's always been this way or if we're only noticing it now, but occasionally the pump will continue to run for around 15 minutes after the bath taps or shower has been switched off. Before I make my self look like an idiot and incur a call out charge for potentially no reason, does anyone know if this is normal?