2026-07-22

Why Is My Radiator Cold at the Top But Hot at the Bottom?

This is one of the most common heating complaints we hear, and thankfully it's usually one of the simplest to fix.

What's causing it

Heat rises through water, so if the top of a radiator stays cold while the bottom warms up, there's almost always a pocket of trapped air sitting at the top of the radiator, stopping hot water from circulating through that section.

How to fix it: bleeding the radiator

• ✓ Turn your heating on and let radiators warm up, then turn it off
• ✓ Find the bleed valve (small square fitting) at the top corner of the radiator
• ✓ Using a radiator key, turn the valve slowly anti-clockwise
• ✓ You'll hear a hiss of escaping air - hold a cloth underneath
• ✓ Once water starts to dribble out steadily, close the valve
• ✓ Check your boiler pressure afterwards and top up if needed

When it's more than just air

If you're bleeding the same radiator every few weeks, or several radiators in the house are affected, that points to a bigger issue such as a faulty automatic air vent, a leak introducing air into the system, or a pump that needs attention.

If bleeding doesn't solve it, or keeps coming back, our central heating team can take a proper look at the whole system.