Signs You Need a Power Flush, Not Just a Bleed
A cold radiator doesn't always mean the same problem, and it definitely doesn't always mean you need the most expensive fix. Here's how to tell the difference before you call anyone.
Try this first: bleeding
If a radiator is cold at the top but warm at the bottom, that's almost always trapped air — a 30-second job with a radiator key. This is the cheapest, simplest fix and worth trying before anything else.
Signs it's actually sludge, not air
- Radiator is cold at the bottom, or cold in patches, rather than just at the top
- You've bled it and it's still not heating evenly
- The water that comes out when bleeding is dark, black, or gritty rather than clear
- Your boiler makes a banging or kettling noise, especially on start-up
- Some rooms heat up fine while others barely warm at all
- Your heating bills have crept up without an obvious reason
These point to sludge and debris built up inside the system over years — bleeding won't fix this, because the problem isn't air, it's solid gunk sitting in the pipework and radiators.
What a power flush actually does
A specialist pump and chemical cleaner flush the whole system through, radiator by radiator, clearing out the built-up sludge rather than just moving it around. It restores even heating and takes the strain off your boiler — worth doing before a new boiler install too, so the new unit isn't immediately fighting old sludge.
What we'll actually tell you
If a bleed or a simple balance will fix it, that's what we'll recommend — we won't sell you a flush you don't need. See our Power Flushing page → or get in touch and describe what's happening; often we can tell which one you need before we even visit.
Last updated August 2026 by The Boiler Doctor, York.