Radiators cold upstairs but hot downstairs?
Upstairs radiators that stay cold while the downstairs ones are hot usually have trapped air (air rises to the highest radiators), a system that needs balancing, a pump that is struggling, or sludge slowing the flow. If the upstairs radiators are cold at the bottom, or the water runs black when they are bled, sludge is the likely cause and a powerflush is the fix.
Air rises to the top
Air in a heating system collects at the highest point, which is usually the upstairs radiators. A radiator full of air at the top feels cold at the top and warm at the bottom. Bleeding releases it, but on a sealed system it lowers the boiler pressure, which then needs topping up.
The system is out of balance
Hot water takes the easiest route. If the radiators nearest the boiler (often downstairs) have their valves wide open, they take most of the flow and the upstairs radiators get little. Balancing means setting each radiator’s lockshield valve so the flow is shared fairly. It is a careful job that takes time.
Sludge is slowing the flow
Sludge narrows pipes and blocks radiators. The pump then can’t push enough water to the far end of the system, and the upstairs radiators lose out first. The signs are radiators that are cold at the bottom, black water when you bleed them, and a boiler that is noisy or slow to heat the house.
The pump
A pump that is set too low, worn or sticking can heat downstairs but not reach upstairs. An engineer can check its setting and whether it is working properly.
Hot upstairs, cold downstairs?
The reverse is less common. In older homes with gravity-fed pipework, or where pipes run under the ground floor, it can point to blocked pipes or sludge on the downstairs circuit.
In Kent?
Kent Powerflush, Gas Safe 660156, covers Faversham, Canterbury, Whitstable, Herne Bay, Thanet, Sandwich, Deal, Dover, Folkestone, Ashford and Sittingbourne, up to Maidstone, Sevenoaks and Gillingham, and Rye.
Local pages: powerflush in Canterbury, powerflush in Margate, powerflush in Sandwich, or see all the areas we cover.
Questions people ask
Why are my upstairs radiators cold after bleeding?
If bleeding didn’t help, the cause is more likely sludge, balancing or the pump than air. Cold patches along the bottom point to sludge.
Will a powerflush fix cold upstairs radiators?
If sludge is the cause, yes. A powerflush clears sludge from every radiator, the pipes and the boiler, so the hot water can reach the whole house again.
Can I just turn the downstairs radiators down?
Turning down the downstairs radiators can push more heat upstairs for a while, but it doesn’t fix the cause. Proper balancing, or clearing the sludge, does.
Related guides
Hot radiators across East Kent
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