When one radiator stays cold while the rest of the house heats up fine, the cause is usually local to that radiator rather than the boiler. We diagnose and fix radiators not heating properly across homes in Cheam and Sutton.
The most common causes are trapped air, sludge build-up inside the radiator, or a valve that is not fully open or has seized. Where a cold radiator is at the far end of a system, poor water balancing across the system can also be a factor.
A few checks can help narrow down the cause before an engineer visits, which are covered below.
Common causes of one cold radiator
- Trapped air, usually causing a cold patch at the top
- Sludge or debris settled at the bottom of the radiator
- A closed, stuck or seized valve
- A faulty thermostatic radiator valve (TRV) head
- Poor balancing across a system with several radiators
How to tell what is causing it
Cold at the top but warm at the bottom usually means trapped air. Cold at the bottom but warm at the top usually means sludge. Uniformly cold with warm pipework nearby often points to a valve that is not letting water through.
Checking valves
Check both the manual valve and the TRV (if fitted) at either end of the radiator are open and not stuck in a closed position.
What an engineer checks
Beyond bleeding the radiator and checking valves, an engineer will assess whether sludge is likely to be affecting other radiators too, and whether a power flush would be worthwhile rather than repeatedly bleeding individual radiators.
How charging works
Diagnosing and fixing a cold radiator is charged by time at our standard hourly rate, plus any parts such as a valve or TRV head. See /our-rates for current rates.
