Cold at the top, warm at the bottom
Trapped air. Bleed the radiator with a bleed key (see our how-to-bleed-radiators guide).
Cold at the bottom, warm at the top
Sludge build-up. Iron oxide sediment settles at the bottom of radiators and blocks flow. A power flush or magnetic filter fit resolves this — common on systems over 8 years old across KT postcodes.
One radiator completely cold
Check the TRV (thermostatic valve) hasn't seized in the closed position — remove the head and press the pin, it should spring back. If the pin is stuck, the valve needs replacing. Also check the lockshield valve at the other end is open.
Upstairs cold, downstairs hot (or vice versa)
System imbalance — the pump isn't distributing flow evenly. Balancing the lockshield valves resolves this. It's a common tune-up job on Kingston terraces and Twickenham flats.
All radiators lukewarm
Boiler thermostat set too low, failing pump, or blocked heat exchanger. Turn the flow temperature up to 70–75°C. If radiators still don't get hot, book a heating diagnostic.
Radiators not heating evenly? Book a diagnostic across KT & TW.
Call 07932 898534Frequently asked questions
Can I fix uneven heating myself?
Bleeding radiators and freeing TRV pins is DIY. Balancing lockshields, replacing valves, and power flushing are engineer jobs.
How much does a power flush cost?
Typically £450–£800 depending on the number of radiators. See our power-flushing guide for a full breakdown.
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