There are a number of reasons your radiators may not heat up, in this blog I want to look at how you could possibly fix a radiator that isn’t heating when all the others in the house do.
The first thing to do is run your boiler for half an hour to get the system hot.
Once the radiators are hot put your hand on the pipes going to the cold radiator, if one or both are hot and there is heat at the bottom of the radiator you may just need to vent or bleed the radiator.
If both these pipes are cold and all the other radiators are hot you have a flow issue.
In this scenario, the first thing to check is that both the valves are open, if you have a thermostatic radiator valve fitted unscrew the head from the body of the valve and press the button in the middle of the valve body with your finger to make sure it is loose. If it doesn’t move you can spray some WD40 on the body to release it.
If it is a standard valve turn the valve head clockwise until it is closed, then reopen fully by turning it anticlockwise. Once you have that done move to the lockshield valve on the other side of the radiator, unscrew the cap and with an adjustable spanner, try and close then open it the same as you did with the other side, do not force it or you may create a not so lovely water feature in your home.
With any luck you may have heat flowing to the radiator now, the quickest way to check is to feel the pipes to see if they are starting to heat, it may take a minute or two.
If opening the valves and venting doesn’t work turn off all other radiators and see if the cold one heats, this may clear an airlock if there is one. You only need to close one side of the other radiators.
How to bleed/vent a radiator
Before bleeding a radiator I always advise you to turn your boiler and pump off.
Then get your vent/bleed key and a cloth, always have a cloth with you to stop any of the water that comes out spilling on a carpet or wall.
Most vents are a standard size, as are most vent keys, so put the key in the vent and slowly turn it, it may take a bit of elbow grease to get it started but do be careful as they can break easily.
If you are lucky enough to have a vent on the outer edge of the radiator you may also be able to use a spanner to loosen the outer thread to vent it or a flat screwdriver.
If there is air in the radiator you will hear it coming out, as soon as any water starts coming out close it down.