Blocked Central Heating Pipes [hot] May 2026

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.

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. blocked central heating pipes

£850 powerflush + £150 pipe replacement. Alternative cost if I’d ignored it: A new boiler (£3k+) when the heat exchanger cracked from the pressure. Cold at bottom of rads = sludge