Cold Radiator? Do I Need a Plumber?

If you are a DIY person the cold radiator symptoms mentioned below could help you to diagnose the problem in your central heating system and possibly fix it without calling a heating engineer. We do not recommend working on the central heating system if you are not competent to do so. Anyone conducting work on a boiler MUST be Gas Safe registered.

One radiator stays cold?

  • Check if both valves on the sides of the radiator are fully open
  • Do you have a thermostatic valve? If so, the pin in the valve could be stuck and the radiator stays cold because there is no flow
  • A weak or blocked central heating pump does not have enough power to circulate water around the system, especially to the radiators furthest from the boiler
  • Air is in the central heating pipework after a system pressure loss.
  • Radiators are not balanced

All central heating radiators are cold?

  • Faulty central heating pump
  • Faulty controls (room thermostat or programmer)
  • Faulty central heating port valve (if there is one)
  • Faulty boiler

Do not confuse dirty central heating systems with faulty components. We are often asked to clean radiators (power flush) because it is not heating up properly. A power flush will not fix faulty components. Even a dirty central heating system can work but will display different symptoms.

Top of the radiator is cold?

If a central heating radiator is hot at the bottom and cool or cold at the top, it's most likely that air is trapped in the radiator. Bleeding the radiator should solve the problem. If you have a pressurised system, as with a combi boiler, do not forget to top-up the pressure.

Bottom of the radiator is cold?

This problem can be caused by sludge in the radiator and the rest of the central heating system. A power flush is recommended to remove sludge from radiators and central heating system pipes but more investigation is needed. The same symptoms can be caused by:

  • Improperly balanced radiators
  • Very long radiators
  • Partially closed radiator valve (very little flow to the radiator)

Cold radiators downstairs?

If radiators downstairs are not heating up it's very likely that:

  • Pump is broken or failing
  • Pump is blocked with sludge
  • If the boiler is on the top floor or in the loft it may also be a central heating system balancing issue

Cold radiators upstairs but downstairs ok?

  • Feed and expansion tank is empty. The feed and expansion tank is usually located in the loft. Refill the tank so that there is enough water. If the feed and expansion tank was empty, make sure there are no leaks in the central heating system
  • Pipe from the feed and expansion tank is blocked with sludge. In this case, the tank will be extremely dirty and a power flush is recommended
  • A pressurised system with low pressure (not enough water in the system) prevents top floor radiators from heating up. Modern boilers automatically recognise this problem and display an error code but older boilers might not have sensors built into the boiler and will not display any error codes

Posted in Central heating & radiators on Aug 31, 2019