Your questions answered

Question:

One radiator has a big cold spot. How can it be fixed? -KL, Fulwood

Answer:

Cold spots in radiators have two causes. Firstly, it may be sludge, particularly in downstairs radiators – an accumulation of corroded material which prevents the hot water from flowing through it. This generally means your system needs power flushing with a special machine, so you will need to call a plumber. Secondly, the cold spots may mean your system will need rebalancing, especially if the cold spots are in the radiators furthest away from the boiler, where the water flow is weaker. If all the radiator lock-shield valves (not the thermostatic valves which control temperature) are open, water will always take the easiest route and may not flow fully into the radiators most distant from the pump. You can try rebalancing the radiators yourself, though a plumber will have more experience in doing this. You need to get an equal flow of water through each radiator. Shut down all the lock-shield valves and reopen them, counting the number of turns you use on the valve. For the radiators nearest the boiler, count out a certain number of turns to reduce the flow but do not open them fully. For radiators further away from the boiler, open the lock shield valves fully. It is then a question of adjusting valves until you get an equal distribution of water and heat.

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