Fix a cold radiator
Save £50–80 in 20 mins — no heating engineer needed
Most people call a heating engineer for this. You probably don't need to.
Last updated: March 2025
Only basic tools needed — most homes already have them.
Before you start
First work out which part of the radiator is cold — hot at the top and cold at the bottom means sludge; cold at the top with hot at the bottom means trapped air (bleeding needed).
This guide covers the two most common causes: trapped air (bleed it) and a stuck valve (open it). Both are simple fixes.
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Tools & materials
- ✓Radiator bleed key— most homes have one — buy if not
- ✓Small cloth or old towel— to catch the drip when bleeding
- !Flat-head screwdriver or pliers— buy — to adjust the lockshield valve cap if needed
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Identify the problem
With the heating on, feel across the radiator with your hand. Cold at the top = trapped air — go to step 2. Cold at the bottom only = sludge (needs a power flush — call a heating engineer). Completely cold = closed valve — go to step 4.
Most people get this done in under 5 minutes.
Where beginners go wrong
Not having a cloth ready when bleeding — water squirts out without warning once the air escapes.
Leaving the bleed valve open — it only needs a quarter-turn and should be closed as soon as water appears.
Forgetting to check boiler pressure after bleeding — bleeding releases water from the system and drops the pressure.
Stop and call a heating engineer if...
The radiator is cold at the bottom — this is sludge and requires a power flush
Multiple radiators throughout the house are cold — indicates a circulation problem
The boiler pressure drops to zero within 24 hours of repressurising
Cost breakdown
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
Want everything in one go? Get it on Amazon
What you just learned
You now understand how air and circulation affect radiator performance. You know how to bleed radiators, read TRV settings, and identify when a problem is beyond a simple fix.
Most people would pay a tradesperson for this.
⚠️ Watch out if you rent
Landlords are responsible for a functional heating system. Bleeding a radiator is reasonable self-maintenance. If a radiator is cold due to a faulty valve or sludge, report it in writing.