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 pin stuck
The valve remains closed even when turned up.
Lockshield closed
The return side may have been shut during balancing.
Air trapped
The radiator may be partly or fully airlocked.
Local blockage
Sludge can block the valve, tail or lower panel.
Symptom variations Match the exact heat pattern, sound or leak position. ⌄
- All other radiators work
- One pipe stays cold
- TRV setting makes no difference
- Heat returns briefly after bleeding
- Radiator warms when tapped
Quick checks Simple checks before removing fittings. ⌄
- Confirm the heating is on.
- Check whether one radiator or the whole system is affected.
- Inspect TRV and lockshield positions.
- Look for leaks, air and corrosion.
- Let the system cool before bleeding.
Step 1 — Confirm it is a local fault Turn the heating off and allow the radiator to cool first. ⌄
Check the boiler and other radiators are normal.
Step 2 — Check TRV and lockshield Turn the heating off and allow the radiator to cool first. ⌄
Make sure both sides are open and not damaged.
Step 3 — Bleed and retest Turn the heating off and allow the radiator to cool first. ⌄
Remove trapped air and run the heating again.
Common causes explained Why radiator faults develop. ⌄
When only one radiator is cold, the fault is usually local to its TRV, lockshield, bleed condition, pipework or internal sludge.
Advanced diagnostics Heating-engineer checks and repair work. ⌄
- Remove and test TRV head.
- Inspect valve pin and lockshield.
- Flush radiator and tails.
- Check local pipework for blockage.
Parts that may need replacing Common components linked to this fault. ⌄
- TRV head
- TRV valve body
- Lockshield valve
- Radiator tail
- Bleed valve
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.