The first thing I noticed was how differently it behaved compared to the others. Every radiator cooled gradually when the boiler stopped firing, but this one faded almost instantly. That’s usually a sign of weak circulation — the water inside isn’t staying hot long enough because fresh hot water isn’t cycling through consistently.
1. Lockshield Too Tight = Heat Drops Fast
In my case, the lockshield was barely open. The radiator heated during the initial push but didn’t get enough flow to keep that heat topped up. Once I opened it slightly, the radiator didn’t just heat faster — it held its warmth properly.
2. Air Pockets Make Heat Vanish Quickly
Air doesn’t just stop a radiator from heating — it can stop it from staying hot. The water circulates poorly, and the top section cools first. Bleeding mine made a noticeable difference.
3. Sludge Makes Radiators Cool Down Faster
Sludge doesn’t just slow heating — it also makes radiators cool quickly because the hot water can’t move freely inside. It’s like the radiator warms in patches instead of evenly.
If your radiator also heats unevenly, this article will help:
Radiators Heat Unevenly Across the House
4. What Fixed Mine
After slightly opening the lockshield and bleeding the radiator properly, the heat stayed consistent. No dramatic fixes needed — just better flow.
For a full breakdown on improving warmth across your home, here’s the main guide:
How to Keep a UK Home Warm for Cheap (Complete Guide)
