Help & Diagnosis

    Radiator cold at the top, bottom or all over?

    Where the radiator is cold tells you the fault: cold at the top means trapped air (bleed it), cold at the bottom means sludge (power flush), and cold all over means a valve issue.

    Common causes

    1. Cold at the top — trapped air

    Air rises and collects at the top. Bleed the rad with a key until water flows out steadily.

    2. Cold at the bottom — sludge

    Iron-oxide sludge sits in the base of the radiator. This is the classic symptom that says your system needs a power flush.

    3. Cold all over — closed valve

    TRV stuck closed, or the lockshield needs balancing. Both fixable in minutes.

    4. Whole system runs cold

    Could be the pump, the diverter valve or sludge restricting flow. Engineer needed.

    Try these first

    • Bleed any radiators that feel cold at the top.
    • Check TRVs are open (turn the head fully clockwise, then back).
    • Top boiler pressure back up after bleeding.

    Still stuck?

    If bleeding hasn't fixed it or your system is full of sludge, we offer professional power flushing across Dereham, Norwich and Norfolk.

    Call 07508 207 799