Cold at the bottom, warm at the top usually means sludge. Here's how to diagnose it and when to book a power flush. Call 020 8050 9933.
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If a radiator is warm at the top but cold at the bottom, air isn't the problem — sludge is. Iron oxide and debris settle at the base of the radiator, blocking hot water flow. Left untreated it damages the pump and heat exchanger. Here's how to check and fix it.
Cold at the top → bleed the radiator (trapped air). Cold at the bottom → sludge (needs flushing). Cold all over → valve closed, pump failing, or airlock further up the system.
Turn the thermostatic radiator valve fully open (usually setting 5). Some valves stick — gently tap the pin with a spanner handle to free it.
We connect a magnetic flushing unit and circulate cleaning chemicals through the system at high velocity. Takes 4–6 hours and restores full flow.
Fit a magnetic system filter (Magnaclean) and add corrosion inhibitor annually. Boiler manufacturers now require this to honour warranties.
Chemical inhibitor and hot flush yes, but a proper power flush needs pumps and gauges beyond DIY tools.
Every 5–8 years, or whenever fitting a new boiler.
Not if done correctly. We inspect for pinhole corrosion first and quote replacements if needed.