guide
Radiator cold at the bottom
Why a radiator heats at the top but stays cold below, and what sludge or balancing problems mean.
What the symptom means
A radiator that is warm at the top and cold at the bottom often contains sludge or magnetite settled in the lower section. Air causes the opposite pattern (cold top). Thermostatic radiator valves (TRVs) stuck closed or a system out of balance can also leave individual radiators underperforming.
What you can check
- Confirm the TRV head is set to open and remove it briefly to see if the pin underneath moves freely (press gently — do not force a seized pin hard).
- Compare other radiators; if several are cold at the bottom, system water quality is suspect.
- Bleeding will not fix sludge — skip repeated bleeding if the top is already hot.
- Note boiler pressure and any recent inhibitor history for the engineer.
Safety notes
- System water can stain; protect floors if a valve is opened.
- Do not dismantle radiators full of water without isolation and a plan to catch the contents.
- Gas boiler faults linked to circulating issues need Gas Safe registered engineers for gas-side work.
When to call a professional
Ask for radiator repair or discuss power flushing when sludge is widespread. Bleed guidance is here: how to bleed a radiator. Book through 01332 314146 or /get-a-quote/.