--- title: "Radiator Not Heating Up? Common Causes and Quick Fixes" description: "A radiator not heating up usually means trapped air, a stuck TRV pin, or internal sludge. Diagnose the fault in under a minute and fix most cases yourself." published: "2026-06-10T09:00:00Z" author: "Reion Akim" category: "Central Heating" content_type: "BlogPost" intent: "informational" business: "R.W. Miller Plumbing & Heating" gas_safe: "919881" service_area: "South London, Surrey" canonical: "https://rwmiller.com/blog/radiator-not-heating-up/" markdown_url: "https://rwmiller.com/blog/radiator-not-heating-up.md" --- # Radiator Not Heating Up? Common Causes and Quick Fixes A radiator not heating up has one of three causes: trapped air (airlock), a stuck TRV pin, or internal sludge buildup. The first two you can fix yourself in under ten minutes. The third requires a professional flush. A cold radiator is one of the most common central heating issues, and it is usually a fault you can sort yourself once you diagnose where the cold spots are. What a DIY fix will not resolve is a radiator that is cold across the bottom — that points to internal sludge buildup, which requires a professional flush. ## The Diagnostics: One Radiator or the Whole House? Before attempting any adjustments, check the other radiators in the property. - If all radiators are cold: The problem lies with your main boiler unit or system pressure, not the individual radiators. - If only one or two radiators are cold: The fault is isolated to those specific units. This is caused by trapped air (an airlock) or a seized valve mechanism. ## 1. Cold at the Top, Hot at the Bottom If the bottom of the metallic panel is warm but the top stays completely cold, air is trapped inside the heating circuit — a common airlock. Because air rises to the highest point, it blocks hot water from filling the upper half of the radiator panel. ### The Quick Fix: Bleeding the Radiator You will need a standard brass radiator key and a cloth to catch any drops. 1. Switch off the central heating and let the system cool for at least 30 minutes to prevent scalding or introducing more air. 2. Locate the bleed valve at the top corner of the radiator panel and insert the key into the central pin. 3. Place your cloth directly underneath and turn the key slowly counter-clockwise. You will hear a distinct hissing sound as the air escapes. 4. Close the valve tightly as soon as the first drop of liquid appears; do not leave it loose. ⚠️ Crucial Next Step: Bleeding releases volume from your sealed circuit, which causes system pressure to drop. Check the gauge on your boiler panel. If the needle is below 1 bar, top it up back to 1.5 bar. ## 2. Completely Cold (But the Pipes are Hot) If the copper pipework leading out of the floor is hot but the radiator panel stays cold, water is being physically blocked from entering. This means the pin inside the Thermostatic Radiator Valve (TRV) — the plastic dial used to adjust the temperature — is stuck down. ### The Quick Fix: Releasing the TRV Pin Over the summer months when the heating is turned off, the internal spring-loaded pin can seize up in the closed position, keeping the valve shut even when you turn the dial to maximum. 1. Unscrew the plastic head of the TRV by turning the chrome collar at the base of the dial counter-clockwise. No tools are needed and no water will escape. 2. Locate the small metallic pin sticking vertically upwards from the brass valve body. 3. Press down on the pin with the flat side of a screwdriver. It should spring back up smoothly. 4. Tap the side of the valve body gently if the pin stays stuck flat. Once it springs back up freely, replace the plastic dial head. ## 3. Hot at the Top, Cold at the Bottom If a radiator has a heavy, distinct cold spot across the bottom centre, your system is suffering from internal sludge buildup. Over time, untreated water reacts with iron components to produce black iron oxide deposits that settle at the bottom of the panel, blocking circulation. ## When to Call an Engineer Unlike trapped air or stuck pins, system sludge cannot be fixed with a simple DIY adjustment. To resolve this, the circuit typically requires a [professional central heating flush](/services/central-heating/) to clear the debris and restore efficiency. Every time you add fresh mains water to a system without chemical inhibitors, you accelerate this internal rust process. To understand how water maintenance protects your heating components, view our guide on [how often a boiler should be serviced](/blog/how-often-should-boiler-be-serviced/). ## Reliable Heating Support across South London If you have tried bleeding your system and checking the TRV pins but your home remains cold, it is time to have the circuit professionally balanced or flushed. R.W. Miller provides honest, transparent central heating service, [Boiler Service](/services/boiler-service/) and [Boiler Repair](/services/boiler-repair/) in South London, including [Wandsworth](/areas/wandsworth/central-heating/), [Bromley](/areas/bromley/central-heating/), [Lambeth](/areas/lambeth/central-heating/), and [Greenwich](/areas/greenwich/central-heating/). Our upfront £80 diagnostic fee covers a full systematic assessment and a fixed-price quote before any repair work starts. Call Reion on 07375 813996 or [make an online appointment](/contact/) for an independent, local assessment. --- *Written by Reion Akim, Owner / Certified Gas Safe Engineer (Gas Safe Registration: 919881). R.W. Miller Plumbing & Heating — South London & Surrey. Call 07375 813996 for a quote.*