Hi my central heating pump keeps stopping and getting red hot. It has 3 speeds. I normally have it on speed 2. It runs for a bit then stops. If I move it to speed 3 it will run again but doesn't sound right. I took it out today and the impellor is clean and moves round freely. I checked the motor resistance and had a reading of about 200ohms. I then put it back in and refilled the system. Turned the heating back on and after a while had the same problem-the pump had stopped and was red hot. I gave it a little tap with a hammer and it started up again. What could be causing it to seize?

Likely the pump is going bad. I've never heard of a CH pump. Is that a model or brand?