Why is my radiator cold at the bottom but hot at the top?
A radiator cold at the bottom is almost always caused by sludge and magnetite buildup settling at the base. A power flush or chemical cleanse will fix it.
Why is My Radiator Cold at the Bottom?
A radiator that's hot at the top but cold at the bottom is one of the clearest signs of sludge and magnetite buildup in your heating system.
What is Happening?
Magnetite (black iron oxide sludge) forms naturally in heating systems over time through corrosion of steel pipework and radiators. It's denser than water and settles at the lowest points — the bottom of radiators.
This sludge layer insulates the bottom of the radiator from the hot water circulating above it, creating the characteristic cold bottom / hot top pattern.
This is Particularly Common in London Because...
London's hard water accelerates corrosion. Many central London properties have older iron pipework. Systems without a magnetic filter (Magnaclean, Fernox TF1) accumulate sludge much faster.
How to Fix It
Option 1: Chemical cleanse — add a descaler/sludge remover to the system, run for a few weeks, then drain and refill with fresh inhibitor.
Option 2: Power flush — the more thorough option, using a high-velocity machine to physically dislodge and remove all sludge.
Prevention
Fit a magnetic filter to the return pipe. We fit Magnaclean or Fernox TF1 on every new installation and power flush.
Call RARE on 020 7458 4949 — we cover all W1, SW1, NW3 postcodes.
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Power Flushing London
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