Radiators Not Heating Up: One Radiator or a Whole Floor

Narrow it down first

Turn the heating on and give it twenty minutes, then go round the house and feel each radiator. The pattern tells you a lot:

• One radiator cold all over, the rest hot: a valve problem, usually
• The radiators nearest the boiler hot, the furthest ones lukewarm: the system needs balancing
• Upstairs cold, downstairs fine: often air, or a zone valve on a two-zone system
• Downstairs cold, upstairs fine: possibly a blockage or a failing pump
• Warm at the top, cold at the bottom: see radiator cold at the bottom

One radiator cold, the rest hot

Check that the control valve is open. Thermostatic radiator valves have a pin underneath the head that can stick down after the summer. Take the head off (most unscrew or pop off) and press the pin gently; it should spring back up. If it is stuck, a few careful taps and some wiggling can free it.

If the valve still will not let water through, or the radiator stays cold with both valves open, the valve may need replacing. Our page on radiator valve replacement explains what that involves.

Far radiators lukewarm: balancing

Water takes the easiest route. If the radiators closest to the boiler are wide open, they grab most of the flow and the ones at the end of the run get little. Balancing means adjusting the lockshield valves so each radiator gets its fair share. Our step-by-step guide on how to balance radiators takes you through it.

Radiator still cold after bleeding

Bleeding lets air out, so if a radiator is still cold afterwards the problem was not air. It may be a stuck valve, a closed lockshield or heavy sludge. Bleeding also lowers the boiler pressure, and if pressure drops too far the boiler may stop heating any radiators properly, so check the gauge afterwards.

If you have not bled radiators before, our how to bleed a radiator guide explains how to do it safely.

Whole floor cold

If a whole floor stays cold, the cause is usually bigger than one radiator. Some homes have separate heating zones for upstairs and downstairs, each with a motorised valve that can fail. A weak or failing pump may push enough water to the nearest radiators but not the far ones. Build-up of sludge in older systems can block pipes as well as radiators. These need an engineer to diagnose, and are part of our central heating work.

Need it sorted? Book a central heating visit

Note which radiators are cold and what you have tried, then call or WhatsApp 07429 632804, or use the quote form.