Radiator Only Gets Warm at the Bottom (How I Actually Fixed Mine)
When a radiator only heats at the bottom while the top stays cold, the room never warms the way it should. I’ve dealt with this issue in more than one property now, and each time the symptoms were the same — the boiler was running, the pipes were warm, but the radiator itself just wasn’t distributing heat properly. It’s one of those problems that looks more serious than it usually is, but it does need sorting because it affects the whole system.
The most common cause is trapped air. Air collects at the top of the radiator and stops hot water from filling the panel evenly, which leaves the bottom warm and the top noticeably cooler. Once I understood that, the fix was much more straightforward. But depending on how your system is behaving, there are a couple of other things worth checking as well.
The first thing I did was bleed the radiator fully. Not a quick bleed — a proper one. On mine, the air took longer to clear than expected, and until it did, the top simply wouldn’t heat. As soon as the flow was steady and the air was out, the radiator heated evenly again.
There are times, though, when bleeding alone doesn’t sort it. In one property, the issue kept coming back because the lockshield valve wasn’t set correctly. When the flow is either too restricted or too open, the radiator doesn’t fill evenly. After adjusting the valve slightly, the radiator held its heat consistently instead of warming unevenly.
If you bleed the radiator and nothing changes, or if the top stays cold no matter what, sludge can be the reason. It doesn’t always block the entire bottom of the radiator — sometimes it settles high enough to affect circulation inside the panel. I once had to remove and flush a radiator because the build-up inside was stopping the hot water from reaching the top. Once it was cleaned, it worked like it should.
It’s also worth paying attention to your boiler pressure. When my pressure kept dropping, the radiators started behaving differently from day to day. A system with unstable pressure doesn’t circulate water properly, so radiators heat unpredictably. If your pressure isn’t holding, this guide explains exactly what sorted mine: Why Your Boiler Keeps Losing Pressure (And the Fixes That Actually Worked for Me).
If the problem returns repeatedly after bleeding, especially if you regularly find air in more than one radiator, the system may not be balanced. Balancing made a noticeable difference in my last place. Before that, the radiators closest to the boiler dominated the flow while the rest lagged behind. After balancing, the whole system warmed more evenly. If you haven’t done this before, this guide walks through the exact method I used: How to Balance Radiators Properly.
If you’ve bled it, checked the lockshield, looked at pressure and the radiator still refuses to heat properly, then there may be a deeper blockage or an issue elsewhere in the system. But in most UK homes, this problem is caused by trapped air or an imbalanced flow, and once you sort that, the radiator usually behaves as it should.
For a full breakdown of keeping heat inside your home without overspending, this guide is worth starting with: How to Keep a UK Home Warm for Cheap (Complete Guide).
