Why is My Radiator Not Working?

Radiator
Radiator

When your home’s radiator isn’t heating properly, it’s not only uncomfortable—it can also signal deeper issues in your heating system. Below is a more robust diagnostic path, combining checks you can do yourself with insights on when to call a pro.

Through a series of logical checks and this guide, you will be able to determine why your radiator is not working and in some cases rectify the problem.

Step 1: Check Other Radiators & Establish Scope

  • Multiple cold radiators? Then the problem is likely systemic—boiler pressure, controls, diverter valve, pump, or supply lines.
  • Only one radiator cold? Favour investigating local issues: valve problems, air, blockages, leaks, or sludge.

This distinction helps you zero in without needless work.

Step 2: System-Level Checks

Before diving into the individual radiator, rule out system-wide causes:

  • Boiler pressure too low. Combi and sealed systems typically require 1-2 bar of pressure. If it’s too low, hot water can’t circulate.
  • Faulty central heating control/timing. If the control panel is not signalling “heating on,” your radiators won’t warm even if the boiler is functional.
  • Diverter or zone valve fault (for systems with multiple loops). Sometimes water is diverted to hot taps but not the heating circuit.

If all system checks look okay, now move on to the specific radiator.

Step 3: Inspect the Thermostatic Radiator Valve (TRV)

A radiator may appear cold simply because its inlet valve is closed or stuck:

  • Remove the TRV head (often under a cap)
  • Look for the pin in the centre. It should move slightly up and down (a few mm).
  • If the pin is stuck (jammed in closed position), gently tap it or free it. Avoid unscrewing the body or you’ll cause unintended leaks.

If warming resumes after freeing the pin, the valve was the problem. If not, continue investigating.

Step 4: Bleed the Radiator & Handle Residual Air

Air trapped inside the radiator is a frequent reason for “top cold / bottom hot” behaviour:

  • Use a radiator key to open the bleed screw. You’ll hear air hiss — wait until water starts flowing, then close it.
  • If after bleeding, the radiator is still cold (or partially so), there may be further issues (see sludge, blockage).
  • After bleeding, check boiler pressure again, because bleeding can reduce system pressure.

Bleeding is low-effort and one of the first things to attempt, but it won’t fix all problems.

Step 5: Investigate Blockages, Sludge & Flow Impediments

If the radiator is still cold (or has cold spots), there’s a strong chance sludge or debris is interfering:

  • What is sludge? Rust particles, mineral deposits and dirt accumulate over time, turning water dirty and sludgy
  • Sludge tends to settle at the bottom and block the bottom passages or the return side of the radiator. That prevents normal circulation.
  • You might see water discolouring when bleeding or draining. That’s a sign sludge is present.

Remedies:

  1. Manual flush:
    1. Turn off heating, isolate the radiator, drain it.
    2. Remove it (or tilt it) and run a garden hose into the inlets, flushing until water runs clean.
    3. Refit and re-bleed.
  2. Power flushing (professional):
    1. Uses pressurised flows to break up and remove sludge.
    2. Effective for severe buildup, though pressure must be controlled in older systems to avoid damaging valves/joints.
  3. Replace radiator (in extreme cases):
    1. If sludge damage is too extensive, replacing the radiator may be more cost-effective and reliable.
  4. Ongoing maintenance:
    1. Annual boiler servicing can catch sludge formation early.
    2. Using inhibitors (chemical additives) can help reduce future sludge buildup. (Often part of pro maintenance packages.)

Step 6: Check for Leaks

Even a small leak can let air in, reduce pressure, and hamper performance.

  • Locate the leak: Dry the radiator and pipes, then use paper or blotting to spot moisture.
  • Common leak locations:
  • Radiator body (often rust/“pinholes”)
  • Bleed valve
  • TRV valves or spindle
  • Union couplings on inlet/outlet pipes

DIY leak checks & fixes:

If from the bleed valve: tighten the screw or replace the valve.

  • If from TRV spindle: more complex; may require replacement or professional repair.
  • If from pipe joints/unions: switch off heating, let the system cool, and tighten the nuts gently. Metal contracts when cold, so tightening is easier then.
  • Leaks from radiator body (pinholes): these are tough/impractical to repair reliably. Usually replacement is required or a temporary sealant (only as a stop-gap) is added to expansion tank.

Leaks left unchecked can worsen and lead to substantial water damage, which may affect insurance claims

Summary Diagnostic Flow (Checklist)

  1. Are multiple radiators cold or just one?
  2. Check boiler pressure, controls, diverter.
  3. Inspect and unstick the TRV pin.
  4. Bleed the radiator; recheck pressure.
  5. Look for blockage/sludge—flush manually or call for power flush.
  6. Check for leaks and repair or replace parts as needed.
  7. If all fails or system is complex, call a Gas Safe engineer.

If your central heating radiator is not working or some radiators are not working, and you’re not sure what to do next. Give us a call!