If your radiators aren’t heating up, the cause can vary depending on the specific issue. Even with professionally installed radiators, maintenance is key to keep the heating at its best.
Usually, your radiators aren’t heating because of either trapped air, a stuck valve, or boiler pressure issues. If only one radiator in your house is cold, it may need bleeding or a valve replacement. If multiple radiators are cold, check your boiler thermostat or the central heating pump.
Read more: What temperature should my radiators be?
This guide will cover all of these issues, how to recognise them, and how to resolve them.
When one radiator isn’t heating up
If one radiator isn’t heating, the problem is with the radiator itself. The silver lining is that it usually doesn’t indicate a problem with the entire system.
A single radiator not heating while the others do indicates trapped air preventing hot-water circulation.
Is the radiator cold at the top?
This is usually trapped air. If you notice this is the problem, you’ll need to bleed them.
Bleeding your radiators is actually a pretty easy process if you know what you need and what you’re looking for.
You’ll need a radiator key, which is pretty common in most DIY/hardware stores. Once you’ve got one, look for the bleed valve, a small square piece (or pieces if it’s a double radiator) at the top of one of the radiator ends.
If you’ve located the bleed valve, turn off the heating. Wait a little while for the radiators to cool down, then use a rag or cloth to hold around the key to protect your hand from the water that will begin to flow out of the radiator.
Insert the key into the valve and turn it slightly until you hear a hissing sound. Let this air out, and when the valve begins to spit water and make a bubbling noise, turn the key the opposite way to lock the bleed valve.
If you’ve managed to do so, you should find that your radiator warms up at the top again.
Is the radiator cold at the bottom?
A radiator that’s cold at the bottom but hot at the top almost always indicates a build-up of sludge, such as rust or dirt, that has settled at the base and is blocking the flow of hot water around the radiator.
To remove sludge from a radiator yourself, you’ll need to detach it, flush it with a hose outside to dislodge the buildup, then reattach and refill.
Sludge removal is a tough DIY job, so if you’re not familiar with plumbing, it’s best left to the professionals.
Is the valve/TRV stuck?
Sometimes, thermostatic radiator valves can seize shut when the internal pin becomes stuck. This is often the case if you’ve not used your radiators for a while, i.e. a summer of warmth.
To fix a stuck radiator TRV pin, first turn off the heating system. Once the TRV head is turned off and cooled, remove it and inspect the pin; if it’s fully sunken, it’s likely stuck. Apply a penetrating oil, like WD-40, to the base and let it soak for five minutes.
Work the pin up and down with a flat-head screwdriver until it moves freely. Avoid using excessive force so that you don’t damage the pin itself. If possible, briefly flush water from the lockshield side to clear any debris.
Reapply oil to stubborn pins, and once the pin moves smoothly, reattach the TRV head and restart your heating system.
The radiator should then heat up and respond to the valve setting.
When all of your radiators aren’t heating up
When no radiators are working, this usually indicates a larger problem with your central heating. This could be a fault with your boiler or a low-pressure issue.
So what should you do?
Check your boiler pressure
Your boiler pressure should be between 1 and 1.5 bar for your ideal temperature. If you’re having an issue with this, you’ll need to top up your boiler pressure.
Read more: How do I reset the pressure on a Worcester Greenstar boiler?
Check the diverter valve
No issue with your hot water, but heating is still not working? This could be due to the diverter valve being stuck.
Your diverter valve directs water either to your taps or to your radiators, so if it sticks in the hot-water position, your heating system won’t get any flow.
This can also explain why you do not have hot water while your heating system is still running, as it works both ways.
If this is the case, it’s best to get a professional heating engineer. Your diverter valve lives inside your boiler, and to access it, you’ll need to strip the boiler down.
When your radiators are only getting lukewarm
If your radiators are warm but not hot, it’s likely due to a system imbalance. This means your hot water isn’t reaching the furthest radiators efficiently enough, so you’ll find some radiators are reaching the ideal temp, whereas others aren’t getting enough heat.
How to balance your system
Turn off the heating
Switch off your heating and let all radiators cool completely. Bleeding them first helps with accuracy.
Open all radiator valves
Open all radiator valves by turning them anti-clockwise. Remove any covers, if needed, and use a spanner or key for the lockshield valves.
Check heating speed
Turn the heating back on and note how quickly each radiator heats up. The closest to the boiler will usually heat first. Then, turn the heating off and let the radiators cool again.
Adjust the fastest radiator
Once cool, turn the heating on. For the fastest radiator, close its lockshield valve, then open it a quarter turn. Measure the temperature at both ends of the radiator and adjust the valve until there’s a 12°C difference between them.
Repeat for all radiators
Balance the rest in the order they heat up. Radiators further from the boiler may need their valves opened more. This ensures even heat distribution throughout your home.
A final thought
Radiators not heating up can come down to a handful of issues: trapped air, a buildup of sludge, or the system just being a bit out of balance.
If you’ve tried the quick fixes and nothing’s changing (or you’re not really sure what you’re looking at), it’s probably time to call a qualified heating engineer to get your heating back on faster, especially when it’s freezing out.
