The good news is that radiators rarely “fail” on their own. If bleeding didn’t work, it means something else is stopping hot water from reaching the radiator — and that’s almost always fixable without calling out a heating engineer.
You Might Have Bled the Radiator, But the System Isn’t Pressurised
After bleeding a radiator, the boiler pressure often drops. You might not notice it, but your boiler will. If the pressure drops too low, the boiler simply won’t push enough water around the system. The radiator you bled then becomes one of the first to stop heating.
Check your boiler’s pressure gauge. If it’s sitting under 1 bar, especially near the bottom end, top it up to around 1.2–1.5. I once bled two radiators in a row and didn’t realise the boiler pressure had tanked — suddenly half the house wouldn’t heat. Adding pressure sorted it instantly.
The Lockshield Valve Might Be in the Wrong Position
Most people never touch the lockshield valve (the one hidden under the plastic cap), but if it’s nearly closed or fully closed, no amount of bleeding will help. The radiator simply isn’t getting flow.
If the radiator stays cold but the pipe on the inlet side is warm, your lockshield valve is almost certainly restricting water. Even turning it a quarter-turn open can bring a radiator back to life.
I cover full radiator balancing here if you want a deeper look:
How to Balance Radiators Properly.
There Might Be Sludge Blocking the Bottom of the Radiator
Bleeding only removes air at the top — it does nothing for sludge at the bottom. If your radiator is cold at the bottom, warm at the top, or lukewarm across the whole surface, sludge is almost guaranteed to be the problem. The older the system, the more likely this is.
Sludge slows down the flow so much that hot water barely circulates. Bleeding won’t even touch it because the sludge sits below the bleed point. A simple sign is when the radiator takes ages to heat, then cools down faster than every other radiator.
Your TRV Might Be Stuck (Very Common)
If you have a thermostatic radiator valve (TRV) and it’s been set low for months, the pin inside can stick in the closed position. You can bleed the radiator a hundred times — no hot water will enter if that TRV pin isn’t lifting.
Take the TRV head off and check the little metal pin underneath. It should move up and down when gently pressed. If it doesn’t move, it’s stuck. A tiny wiggle with pliers usually frees it.
It’s one of the easiest fixes you can make, and loads of people don’t even realise it’s a thing.
The Radiator Might Not Be Getting Priority Flow
If your radiator is on a long circuit or sits far from the boiler, it relies on strong flow from the pump. After bleeding, the pressure drop or slight flow imbalance can push it to the bottom of the priority list — meaning the closer radiators heat first and yours barely gets anything.
This is exactly why balancing your system matters. Radiators closest to the boiler hog all the flow unless you restrict them a little. Once they’re slowed down, the weaker radiators finally get enough water to heat properly.
If other radiators in your house are heating too fast, that’s a huge sign of imbalance.
The Pump Might Be Running Weak
A weak or failing circulation pump won’t push hot water around the system properly, so radiators at the end of the circuit can stay cold. Sometimes pumps don’t fail suddenly — they just get weaker over time. You’ll notice that radiators heat slower and slower every winter.
If your downstairs radiators stay hot but upstairs remain cold (or vice versa), that’s another clue the pump isn’t pushing evenly.
You Might Have Air in the System, Just Not at the Radiator
Air can get trapped in pipework as well as radiators. If the pipe leading to the radiator has an air pocket, the radiator won’t get proper flow even if it bleeds normally. Sometimes turning off every other radiator and forcing heat only into the cold one helps push the air pocket out. It’s a quick thing to try before assuming anything else has failed.
What to Try Before Calling Anyone Out
If bleeding didn’t work, go through these steps:
• Check boiler pressure (top it up if it’s low)
• Turn the lockshield slightly open
• Test the TRV pin
• Feel the pipes — if the inlet is hot but radiator isn’t, it’s a flow issue
• Turn off all other radiators temporarily to force heat into the cold one
• Check for cold-bottom sludge
One of these fixes usually gets the radiator heating again.
How This Links to Heating Your Home Properly
A single cold radiator drags the whole system down. The boiler has to work harder, the house heats unevenly, and you end up using more gas than you should. Getting every radiator working properly makes your whole heating system more efficient — and cheaper to run.
If you want a full strategy for making your home warm without wasting money, I break it all down here:
How to Keep a UK Home Warm for Cheap (Complete Guide).
