There is a logical procedure to follow when troubleshooting an appliance or a system such as your hot water system. There are many manufacturers of boilers, pumps, and accessories. Each heating system is custom assembled to meet the pattern of the house.
Imagine calling an automobile dealer and telling him that your car won’t start. What would be the things he would need to know in order to help? Would he have to know the manufacturer and the model of the car?
Heating systems require the same information. There are some pumps that become ‘stuck’ and need to be loosened and restarted. This is best done by a person who knows how to start the pump without damage. He would first need to be able to identify if it is that pump.
Have you given the necessary information to identify any part of this system other than that of a gas hot water system with a circulator of unknown manufacture? A licensed plumber would know by sight what to do.