a woman checking her radiator thermostat because her heating is on but the radiator is cold

My Heating Is On But The Radiators Are Cold – What’s Wrong?

The heating is on but the radiators are cold is a common breakdown callout that engineers visit. Suddenly, your cosy home is without heat, but you have done all the things you are supposed to do. The heating programmer is calling for heat, your app is up-to-date and signalling your room thermostat, and the boiler is switched on. But the radiators are stone cold. What is happening? And is it something you can fix without the need of a callout fee? This blog is here to help you if this is a scenario you face right now. So let’s get straight to it.

What Type Of Boiler Do You Have?

If the heating is on but the radiators are cold, there could be several possible issues. First, we need to determine what type of central heating system you have. Do you have a combination (combi) boiler, or do you have a hot water cylinder in your home? If you have a combination boiler the boiler will only perform one function at the time, so it will only do heating, or it will only do hot water, it won’t do both.

What is key with this functionality is that it prioritises hot water, so if the hot water tap or shower is running, the radiators will not heat up, even when the controls switch on. As soon as the hot water stops flowing, the combi boiler will switch to the heating function. Maybe a tap hasn’t turned off properly, which could lead to an embarrassing callout! Central heating systems with a hot water cylinder do not prioritise hot water, so will not have this issue.

Has The Boiler Locked Out?

The boiler is a likely source of the problem why the heating is on but the radiators are cold. The boiler will protect itself and the system if something isn’t right. It may be that the boiler needs resetting, which on many boiler models flashing or different coloured lights, or it may display a fault code. Refer to your manufacturer’s instruction to check what the sequence or codes relate to.

A common fault in this situation is the boiler is low on pressure. A pressure gauge on some boilers shows the current pressure in the system. Pressure below 0.5bar is likely to trigger s safety lockout in most boilers. You can top up the system pressure by following the manufacturer’s instructions, or the process explained to you by your boiler installer. This is a common fault after people bleed radiators. As modern systems need manually filling after bleeding radiators, we often forget this, or weren’t informed about this process.

When To Seek Help

Most other fault codes on boilers will require a professional to look at the boiler, but refer to the manufacturer’s instructions for peace of mind. There could be a number of circulation issues from a labouring pump or a faulty diverter valve, to more serious issues regarding circulation and water quality.

If you have any issues or would like a quote for a new boiler please get in touch.

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