Hi network. Just wanted to say my heating pump started jamming up about once every month. I, like you tapped it with a mallet to get it going again but it got progressively worse untill it stopped completely. Just thought I'd warn you as it will always stop completely on the coldest day of the year. The impeller on mine had got furred up. I would find out about getting a replacement incase it does fail completely soon. It might be worth flushing the heating system to clean it out and then adding some corrosion inhibitor such as Furnox to the system.