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RADIATOR FAULTS

Radiator Cold at the Top

A radiator that is warm at the bottom but cold at the top usually contains trapped air, though low system pressure or circulation problems can also contribute.

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Turn the heating off and allow the system to cool before bleeding or adjusting radiators

Radiators contain hot pressurised water. Stop if a fitting is seized, leaking heavily or boiler pressure repeatedly drops.

MOST LIKELY CAUSES

Start with these

Trapped air Air collects at the top and stops hot water filling the panel.
Low boiler pressure Insufficient pressure can reduce circulation.
Recently drained system Air often remains after maintenance or refilling.
Local circulation issue A partly closed valve or restriction may reduce flow.
◫ Symptom variations Match the exact heat pattern, sound or leak position. ⌄
  • Top section stays cold
  • Gurgling noise
  • Radiator heats after bleeding
  • Pressure drops afterwards
  • Several upstairs radiators affected
✓ Quick checks Simple checks before removing fittings. ⌄
  1. Confirm the heating is on.
  2. Check whether one radiator or the whole system is affected.
  3. Inspect TRV and lockshield positions.
  4. Look for leaks, air and corrosion.
  5. Let the system cool before bleeding.
1 Step 1 — Cool the system Turn the heating off and allow the radiator to cool first. ⌄

Turn the heating off and let the radiator cool before opening the bleed valve.

2 Step 2 — Bleed carefully Turn the heating off and allow the radiator to cool first. ⌄

Open the bleed valve slowly and close it when water appears.

3 Step 3 — Check pressure Turn the heating off and allow the radiator to cool first. ⌄

Inspect boiler pressure afterwards and repressurise only as instructed.

⌁ Common causes explained Why radiator faults develop. ⌄

A radiator that is warm at the bottom but cold at the top usually contains trapped air, though low system pressure or circulation problems can also contribute.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Check automatic air vents.
  • Inspect circulation and pump performance.
  • Confirm expansion vessel condition.
  • Check for system leaks.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • Bleed valve
  • Automatic air vent
  • Radiator valve
  • Pressure-related components
! When to call a heating engineer Conditions that should end basic troubleshooting. ⌄
  • Boiler pressure keeps dropping.
  • A radiator or valve is leaking heavily.
  • Valves are seized or corroded.
  • Several radiators remain cold.
  • The pump or boiler may be faulty.
? Frequently asked questions Common radiator questions. ⌄

Should I bleed radiators while heating is on?

No. Turn the heating off and allow the system to cool first.

Why did boiler pressure drop?

Releasing air can reduce pressure in a sealed system.