If the pump sounds like it’s running, but one radiator or more stays cold, there may be an airlock in the pump. Find the pump and identify the bleed screw. Place a bowl under the pump and open the bleed screw to allow the air out. As soon as the water appears at the screw, tighten it up and test the system. It is always possible that the small feeder tank in the attic is running dry and letting air into the system.

Sometimes the rotor in the pump will stick, and although you can feel a little vibration in the pump, the actual mechanism will not be turning. Some pumps have a cover screw that can be removed to access the spindle of the pump. Turn the spindle with a screwdriver until it is moving freely and test the system. Hampstead Plumbers replace pumps.

There are two types of circulating pump: a single speed (fixed-head), and variable speed. While a variable speed unit is slightly more expensive, it is considerably more flexible than a single speed pump and well worth the extra cost. To adjust the speed of a central heating pump, there is usually a small rotary switch. Some pumps require you to remove a cover or use a very small screwdriver or allen key.
A Hampstead Plumber can adjust the speed.

Sometimes the pump impeller will jam on a bit of pipe scale and the system will fail to heat up. Before deciding to replace the pump, have a quick look to see if this is the case, if it is, remove the debris and refit the pump. Make sure that the entire system is completely free of debris before a new pump is fitted.

Control valves are electrically driven. Before replacing a valve, check that the control unit, power supply and wiring are all okay. Some systems are fitted between two large service valves. This is very useful in that you don’t have to drain the entire central heating system to take the pump out. These make it easy and convenient to change the pump and can be inspected easily.
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