Diagnose a radiator that isn't warm enough

When the rest of the radiators in your house are working properly, but one stubbornly refuses to warm up, run through the following checklist:

  • Is the radiator valve closed?
    The handwheel valve that allows hot water in to the radiator may be closed; this can be turned to the open position by hand.
  • Is the radiator thermostat valve set correctly and working?
    If your radiator has a thermostat, check that the valve hasn't been set too low. If this valve is faulty then it will need to be replaced and central heating system drained.
  • Is the lockshield valve set correctly?
    The lockshield valve sits at the opposite end of the radiator to the handwheel valve. The lockshield controls hot water flow into the radiator and may need adjusting to let more hot water through.
  • Are the valves blocked?
    Radiator valves may stop working if they are blocked by limescale. If this is the case then the radiator may need flushing out or the system may need descaling.

If the radiator still isn't heating up, solving the problem will depend on where it's located.

Upstairs radiator

If the upstairs radiators in your home are cold, it's an indication that the feed and expansion tank in your loft has run dry. This usually points to a larger problem. However it's also possible that the the ball valve in the tank isn't working correctly; it may be blocked or jammed. Try the following:

  1. Clear any obstructions to the ball valve.
  2. Refill the cistern, making sure there is enough room for the water to expand when the system heats up.
  3. When the system is cold there should be just enough water to make the ball float and switch off the water coming in.

Downstairs radiator

This is an indication that the pump is faulty. Replacement will require a Gas Safe Register approved professional.

Don't forget

It's highly recommended that you seek the skills of a Gas Safe Register approved heating engineer when you have major boiler or heating problems. Also, remember that all boilers and heating systems should be regularly checked and serviced by a professional.

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