It started subtly. The living room radiator was lukewarm at the top but ice cold at the bottom. Then, the bedroom radiator went completely cold. The final straw was the boiler pressure dropping daily and the pipes making a sound like a boiling kettle. The giveaway? When I turned the heating on, one pipe to a radiator stayed stone cold while the other was hot.
Cold at bottom of rads = sludge. One pipe hot, one pipe cold = blockage. Drain, cut, vacuum for a DIY fix if you’re handy, but realistically, book a powerflush and fit a magnetic filter. Your boiler will thank you. Disclaimer: I am not a plumber. This is my experience as a homeowner. Always consult a Gas Safe engineer (UK) or licensed HVAC tech (US) before cutting into your heating system. blocked central heating pipes
Locate the blocked pipe: Use an infrared thermometer or just feel along the pipe run. You'll find a spot where the pipe goes from hot to cold in 2 inches. Method: Isolate the system, drain below the blockage, cut the pipe, and use a wet-dry vacuum on the open end. I sucked out a golf-ball sized clump of black sludge. Then, I fed a drain snake (yes, a plumbing auger) into the pipe to break up the rest. Warning: This is messy, and if you have microbore (8-10mm) pipes, you will likely puncture them. It started subtly
When my plumber cut out the affected section of 15mm copper pipe, it wasn’t empty. It was 90% full of a solid, tar-like black paste. You couldn’t push water through it with a garden hose. This didn't happen overnight—it took 15 years of no system maintenance. The final straw was the boiler pressure dropping
£850 powerflush + £150 pipe replacement. Alternative cost if I’d ignored it: A new boiler (£3k+) when the heat exchanger cracked from the pressure.