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My boiler works but radiators are cold

If your boiler is working but your radiators are not heating up or are cool, then it is likely that you have a problem with either your central heating controls or your boiler pump. However, before you do anything, you should carry out a few preliminary checks to make sure that it is not a simple problem that can easily be resolved.


First, check your thermostat. Try turning the dial up to a higher temperature, ideally, above 17 degrees. You should hear a distinct click, which indicates that the system is on. Leave it five to ten minutes and check whether the radiators begin to heat up. If your thermostat or timer isn’t working properly, you will need a Gas Safe Register approved engineer to repair or replace it.


If your radiators still don’t heat up, try checking your Programmer. This is a small electrical device with an inbuilt clock. These are normally located in the airing cupboard, bathroom or in the kitchen. The Programmer allows you to control when your heating comes on and goes off. Check that both the central heating (CH) and hot water (HW) are switched on. This may require you overriding the timer to do this.

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✓  A fixed price boiler repair
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If this is unsuccessful, the next step would be to check the motorized diverter valve, located next to your boiler. This valve controls the flow of hot water to the boiler and central heating system. The valve is powered by electricity and acts like a electro-magnet which becomes charged and pulls the valve one way or the other. There should be an obvious switch nearby. Once you find this try turning off the electrical power to the system then try turning it on again.

If this is still unsuccessful, the problem may be with your pump.


The pump acts like a water mill, taking the heated water from the boiler and pumps it with force down the pipes to the taps and radiators. There could either be a blockage along the system or the pump itself could have a problem. The pump is also powered by electricity, so again try turning off the electrical power and see if there is an obvious problem.


You should be able to tell whether you have air in the system if your radiators turn cold alternately. This could be because there is an airlock in your central heating system and the air pockets are moving around the system. Simply bleeding your radiators with the radiator key may solve the problem. If this doesn’t solve the problem, you may need to seek the help of a professional.

We hope the above has helped to indicate what your problem could be; however, if you have any queries then contact us and we’ll deploy a local engineer to repair your boiler so please get in touch.