Why Are My Radiators Cold and What Should I Do If There Is No Heating?
One of the most frustrating heating emergencies is having a running boiler with domestic hot water, yet every radiator in your home remains icy cold.
If your radiators are cold, first identify the pattern: radiators cold at the top need bleeding with a radiator key to release trapped air; radiators cold at the bottom indicate heavy magnetite sludge requiring a chemical flush; a single cold radiator often has a stuck pin inside the thermostatic valve (TRV). If all radiators are cold simultaneously while hot water works, your circulation pump or motorised diverter valve has likely failed.
How Do I Diagnose Why My Radiator Is Cold (Top vs Bottom vs Whole)?
1. Cold at the Top, Hot at the Bottom
This is the classic sign of trapped airlocks. As heated water circulates, air bubbles rise and collect at the top of the radiator panel, preventing hot water from circulating through the upper fins.
Solution: Bleed the radiator using a brass radiator key until water trickles out. (Always check boiler pressure afterwards, as bleeding reduces system pressure).
2. Hot at the Top, Cold in the Centre/Bottom
This indicates a heavy buildup of central heating sludge (corroded black iron oxide). In older Victorian properties in Islington, Camden, and Hackney with aging steel or cast iron pipework, heavy sludge settles at the bottom of panels, restricting flow.
Solution: A chemical system flush, magnetic filter installation, or powerflush conducted by an independent heating professional.
3. Entire Radiator Completely Freezing
Check the thermostatic radiator valve (TRV) head. During long summer months when heating is off, the internal spring-loaded brass pin frequently seizes in the closed position.
Quick Fix: Unscrew the plastic TRV head and gently tap the small exposed metal pin vertically with a coin or small pliers until it springs freely up and down.
All radiators cold simultaneously across the property?
If every radiator is cold while hot water works, your circulation pump or 2-port/3-port motorized diverter valve has likely failed.
Frequently Asked Questions About Cold Radiators
Why are my radiators hot at the bottom but cold at the top?
Air has entered the heating system and naturally accumulated in the top chambers of the radiator panel. Bleeding the radiator with a radiator bleed key will quickly release the air pocket and restore heat.
Why are all radiators cold even though I have hot water?
If hot water works from your taps but all radiators remain cold, the central heating circulation pump has seized or your motorised diverter valve (which directs heated water between taps and radiators) has failed.
How much does it cost to replace a motorised diverter valve in London?
Prices vary by system, part, labour and appointment time. Ask for a written quote that lists diagnosis, labour, parts, VAT and any return-visit fee. See our guide to comparing boiler repair estimates.
In what order should I bleed radiators in a multi-storey London house?
Always start on the ground floor with the radiator furthest from the boiler, work through ground-floor rooms, and then proceed to the top floor, finishing with the radiator furthest away upstairs.