When radiators heat unevenly across the house, it usually isn’t a boiler issue. The boiler is doing what it’s supposed to do. The real story is how the water is travelling around the system, and which radiators are getting priority without you realising it.
1. The Clue Is Always in the Order They Heat Up
In my home, the radiators closest to the boiler warmed up almost immediately. The further away I went, the slower they responded. One bedroom radiator stayed lukewarm until the boiler had been running for a good while. Once I noticed that pattern, everything else started making sense.
Uneven heating isn’t random — it’s the heating system showing which radiators have strong flow and which ones aren’t getting their share.
2. The Lockshields Decide Who Gets the Most Heat
This was the first thing I looked at, and it’s what eventually fixed most of the imbalance. Every radiator has a lockshield valve, and that valve controls how much water flows in and out of that radiator. If one radiator is fully open and another one is nearly shut, you’ll always get uneven heating.
In my case, one of the downstairs radiators was wide open, so it stole most of the flow. The upstairs radiator hardly had any chance. After adjusting the lockshields so each radiator got a more even share, the house heated up far more consistently.
It wasn’t instant — I had to make small changes and test again — but the improvement was obvious.
If you haven’t seen it yet, here’s the proper guide on balancing radiators:
How to Balance Radiators Properly
3. TRVs Can Cause Some Rooms to “Drop Out” Early
I had a TRV in the living room that would shut the radiator off too quickly. The room warmed up fast, and the TRV decided it had done enough, so it closed the valve. Meanwhile, radiators in other rooms were still struggling to heat. It made the whole system feel off-balance.
Once I turned that TRV up slightly (and freed the pin underneath), the radiator stayed active long enough for the rest of the house to catch up.
4. Low Pressure Can Affect Certain Floors More Than Others
One thing I didn’t realise early on is how much pressure affects circulation between floors. When the boiler pressure dipped, the downstairs radiators still heated fairly well. The upstairs ones slowed right down. They didn’t stop completely, but they lagged noticeably every single time.
As soon as I topped up the pressure back to around 1.3 bar, the difference upstairs was immediate. They no longer felt like they were connected to a different system.
5. Pipe Layout Plays a Bigger Role Than You Think
Some houses have heating systems that naturally favour certain rooms because of how the pipes were installed. This isn’t something you “fix” easily, but you can work around it. Balancing the radiators, checking valves, and making sure no radiator is stealing too much flow can make an uneven system behave almost perfectly.
In my place, the living room just happens to be the first on the circuit. Once I toned that radiator down a little, the rest of the house finally started heating more evenly.
6. A Small Amount of Sludge Can Create a Big Difference
Sludge doesn’t always block a radiator completely — sometimes it just slows one down. When that happens, the radiator will eventually get hot, but always later than the others. I’ve had this in a spare room radiator where it never heated at the same pace as the rest. It wasn’t a dramatic problem, but it was noticeable.
Balancing helped, but it wasn’t until the system was cleaned that it fully matched the rest.
If your radiator takes a long time to heat as well, you may want to check this article too:
Radiator Takes Ages to Heat Up
7. Once Everything Is Balanced, You Really Notice the Difference
After sorting my system out, the house heated more evenly, the boiler didn’t run as long, and the cold rooms didn’t feel like they were lagging behind anymore. The whole place just felt more controlled and predictable.
If you’re trying to get your heating system running properly and want to understand how all of this ties into keeping your home warm without wasting money, here’s the main guide with everything in one place:
