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RADIATOR FAULTS

Radiator Not Heating

A radiator may stay cold because a valve is closed or stuck, air is trapped, flow is unbalanced, pipework is blocked or the heating system is not circulating properly.

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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

TRV stuck closed The pin may seize after long periods without use.
Lockshield closed The balancing valve may be shut too far.
Trapped air Air prevents hot water entering fully.
Local blockage Sludge or restricted pipework can stop circulation.
◫ Symptom variations Match the exact heat pattern, sound or leak position. ⌄
  • Radiator completely cold
  • One pipe hot and one cold
  • Heats only when others are off
  • TRV makes no difference
  • Gurgling or partial heat
✓ 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 — Confirm heating demand Turn the heating off and allow the radiator to cool first. ⌄

Check the boiler and other radiators are operating.

2 Step 2 — Check both valves Turn the heating off and allow the radiator to cool first. ⌄

Open the TRV and confirm the lockshield is not closed.

3 Step 3 — Bleed and rebalance Turn the heating off and allow the radiator to cool first. ⌄

Remove trapped air and adjust balancing if flow remains poor.

⌁ Common causes explained Why radiator faults develop. ⌄

A radiator may stay cold because a valve is closed or stuck, air is trapped, flow is unbalanced, pipework is blocked or the heating system is not circulating properly.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Check TRV pin movement.
  • Measure pipe temperatures.
  • Inspect for blocked tails.
  • Assess pump and bypass settings.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • TRV head
  • TRV body
  • Lockshield valve
  • Bleed valve
  • Radiator tail
! 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.