Diagnosing a cold radiator

When it’s chilly outside, it’s no fun coming home to a cold house. If you’re asking yourself, ‘why is my radiator cold?’ our tips on troubleshooting cold radiators could help you stay toasty.

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 into the radiator may be closed; this can be turned to the open position by hand. Check that both valves on the sides of the radiator are open.

Is the radiator thermostat valve set correctly and working?

If your radiator is fitted with 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 the central heating system drained.

Is the lockshield valve set correctly?

The lockshield valve sits at the opposite end of the radiator to the handwheel or thermostatically operated valve. The lockshield valve regulates the flow of water from the radiator and may need adjusting to let more hot water through.

Are the valves blocked?

If the valves are open but the radiator is still cold then the valves may be blocked by debris or sludge. If this is the case then the radiator may need flushing out or the system may need a powerflush.

Cold patches on radiators

If your radiator is cold at the top, but hot at the bottom then it's probable that air is trapped in the system. Bleed your radiators and the problem should be sorted.

Radiator cold at the bottom

It might sound obvious, but first check that you have turned your heating on. If it's on and your radiators are still cold, then your heating system could be affected by sludge, reducing the circulation of hot water.

If you have an open vented heating system you should be able to solve this problem by cleaning your system:

  1. Buy a heating system sludge remover at your local DIY store and use as per manufacturers instructions.

  2.  Add the liquid to the feed and expansion tank.

  3. After a few days you will need to empty and refill the system. Non-open vent systems require you to flush through the radiators with a hosepipe.

Cleaning your heating system can be a big job, so if in doubt get a professional plumber to carry out the work.

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

Cold radiators upstairs

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 ball valve in the tank isn't working correctly; it may be blocked or jammed. Try the following:

  1. The cistern is usually found in the loft.

  2. Clear any obstructions to the ball valve.

  3. Refill the cistern, making sure there is enough room for the water to expand when the system heats up.

  4. Refill the cistern so that there is just enough water to float the ballcock.

  5. When the system is cold there should be just enough water to make the ball float and switch off the water coming in.

  6. Don't fill it up completely, as there must be enough room for the water to expand.

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.

With a full cistern, the upstairs radiators should start heating, but it is a good idea to get a professional plumber in to work out why the cistern ran dry in the first place.

Cold radiators downstairs

If your downstairs radiators are failing to heat up then there's a good chance that your central heating pump has failed or is on its way out. If you're confident in your DIY abilities you may want to read up on how to tackle the problem yourself, but if in doubt then call on the skills of an expert plumber ASAP.

Remember, cold radiators could lead to frozen or burst pipes in winter, so they need to be tackled quickly.

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