Radiators Cold at Bottom

Magnetite sludge from internal corrosion

Steel radiators corrode from the inside, producing iron oxide (magnetite) — a fine, dense black sludge. This settles at the bottom of radiators and in the lowest points of pipework, blocking flow. London's older systems without inhibitor are particularly affected.

No inhibitor or magnetic filter

Systems without corrosion inhibitor produce sludge rapidly. A Fernox or Sentinel inhibitor dose and a magnetic filter (Magnaclean/Fernox TF1) prevent further accumulation after a power flush.

Age of heating system

Systems over 10–15 years old without regular servicing and chemical treatment accumulate significant sludge volumes. Power flushing restores full heat output.

Low-quality fill water

If the system has been repeatedly topped up with untreated tap water, scale and oxygen introduced with the water accelerate corrosion.

Can I fix cold radiator bottoms without a power flush?

Individual radiators can be removed and flushed with a hosepipe, which removes sludge from that radiator. But sludge circulating in the pipework will re-deposit quickly. A full power flush is the only complete solution for system-wide sludge.

How long does a power flush take?

Typically 4–6 hours for a standard London property. Larger or more heavily contaminated systems take longer. We complete the full job in a single visit.

How much does power flushing cost in London?

RARE power flushing starts from approximately £500+VAT for a standard system. We provide a fixed price before starting — no surprises.

How often should a heating system be power flushed?

In most cases, a single power flush followed by inhibitor dosing and a magnetic filter installation prevents the need for future flushes. Servicing the filter annually is sufficient ongoing maintenance.