DEALING WITH COLD RADIATORS
If one or more radiators are cold, or significantly cooler than the rest, suspect an airlock caused by air getting into the system or the presence of gas due to a chemical reaction between air, water and metal.
1. Before you start, turn the system off and give the air a chance to settle.
Hold a container under the valve to catch any drips and then open it very slightly with the key. If there is an airlock, you should hear a hiss of escaping air which will be followed by a dribble of water which gradually becomes a steady flow. When this happens, close the valve.
Occasionally, due to leaks, lack of water in the system. Or a design defect in the pipework, the airlock may be more serious. In this case bleeding the radiators could have no effect.
Open the bleed valve on the affected radiator and get one or more assistants to stand by with containers to catch the drips.
Find the pump (normally near the boiler) and locate the flow regulator. Note what setting it’s on and then. Using a screw driver, turn it full on and then off in 15 second bursts.
If you still have no success, the only other thing to try is bleeding the pump itself.
You should find the bleed valve on top of the pump casing: open and close it again very briefly using a screwdriver — a hiss of air betrays the fault.
2. If the radiator valve itself has seized up, drain the system and dismantle the valve. Clean the jumper gently with wire wool and reassemble it: if you can’t get a replacement rubber 0ring use PTFE tape instead.
Frequency: You’ll almost certainly get airlocks if you’ve had to drain and refill the system.
Pipework problems are less common than pump and radiator faults, though old age and hard water take their toll of pipes, radiators, valves and boilers. The majority of problems are minor ones and easily dealt with
Minimize them by adopting the correct procedure.
But if you are constantly plagued by airlocks or you have to bleed a radiator every week. Suspect another fault. Check that the expansion tank is at the right level: if it is dry, the ball valve has probably jammed. Balancing: Sometimes, what seems like an airlock in a radiator is in fact caused by an incorrectly set lockshield valve. These balance the flow between one radiator and another and are preset during installation. But if the radiator has been removed for any reason, the setting could have been disturbed.
3. If you suspect that this might be the case, remove the cover and use an adjustable spanner to open or close it a few turns to admit hot water to the radiator.