Jammed Rotor:Pump motors can occasionally stick and not run, (this does not mean that the pump needs replacing) and although there may be a slight vibration at the casing, this doesnt mean there is any rotation. Most of these pump motors will have an adjustable cover allowing access to the pumps spindle. Using a medium sized screwdriver to turn the spindle manually will usually free it up and let it spin once again,Air in the Pump:When the pump is running but one or more radiator stays cold, there may be an airlock inside the pump itself. Go to the pump and find the bleed screw. Put a bowl under the pump to catch any trickles of water, then, using a bleed key, open the bleed screw to let the air out. As soon as the water appears at the screw, tighten it up and retest. Boiler Repair London can do this job.Pump Speed Adjustment:The central heating pumps speed can easily be adjusted via a small rotary type of switch fitted to the pump casingThere are three types of circulating pump:Single Speed (fixed head).Automatic Variable Speed Circulator. 3 Speed fixed Head.Note: While a variable speed unit is slightly more expensive it is more flexible which justifies the extra cost.Tools:Usually the pump is situated between two isolating spindle valves, which require two large adjustable wrenches to undo their large nuts. Make sure not to over tighten. Boiler Repairs London carry these tools.Valve Replacement:Controlling valves are normally electrically powered, so if you think there is a problem, always check the cables and terminals visually before you think about trying to replace. Impellers:Sometimes circulating pump the impellers can jams and will not pump. If a pump stops pumping, always check the impeller first as any blockage can normally be removed by hand, sorting the problem.