Air-locked Pump:If a circulating pump runs but some of the radiators remain cold, then, there could be air in the pump itself. Fitted on the pump casing is a screw called a bleed-screw. Place a bowl underneath the pump. This will catch any water, then, use a bleed key to open the bleed screw slowly to allow the air to bleed out. Once water appears, tighten it up and retest. An Archway Plumber can do this job.Speed Adjusting:A central heating pump can have its speed easily adjusted by altering or turning a small rotary style switch fitted that is fitted to the pump casing.Circulating Pumps x 3: Fixed Head (Single Speed), Variable Speed Circulator, Fixed Head (3 Speed).Information: A variable speed unit will cost more, but has a flexibility that really is worth the extra cost.Rotor Sticks:These motors can sometimes stop running. This is usually down to pump motor sticking. The symptom doesn’t mean that the pump will need to be removed and replaced. There may be a light vibration at the casing, but this doesn’t mean that the motor is spinning. The vast majority of these pump motors will have an access cover to expose the pump’s rotor, so, with a medium sized screwdriver you can turn the rotor manually. This usually frees it up.Pump Removal:Most pumps are situated between two isolating spindle operated valves, which need two large adjustable wrenches to undo their large nuts. Make sure not to over tighten. Archway Plumbers carry these tools.Valve Replacement:Control valves for these systems are normally electrical, so if you think there is an issue, always visually check the cables and terminals before you consider replacement. Pump Impellers:The pump impellers can sometimes jam and the pump will stop pumping. It is good practice to visually check the impeller initially, most times the impeller block or jam can be removed by hand.