I recently had a new propane water heater installed. At the time of the installation, the plumber told me that the recirculating pump was not working and that this would cause my gas bill to be high. I still have hot water immediately at every faucet in the house, so I question if the pump is bad. It is a Grundfos pump and the installation was done when the house was built (1991), so it is the type with the extra return line, not the type that can be added to any water system. Can you tell me why a failed pump would cause in increase in gas use? Would I still have immediate hot water, if the pump was not working?