When your heating system starts acting up, it can be frustrating, especially when the weather turns colder and you need your home to warm up quickly. Some central heating problems are simple to spot, while others can point to a deeper issue with your boiler, radiators, valves, thermostat, or pipework.
Before you panic, there are a few safe checks you can do at home. You might be dealing with trapped air, low boiler pressure, a thermostat setting, or a radiator valve that is not opening properly.
In this guide, we explain the most common central heating problems and radiator problems, what may be causing them, what you can check safely, and when it is time to call a Gas Safe heating engineer in South London.
Common Heating Problems and Issues – Quick Checklist
If you are dealing with a heating problem, central heating not working, or general heating issues around the home, start with this quick checklist. It gives you a fast way to match the symptom with the most likely cause and the safest next step.
| Heating problem | Common cause | First safe check |
| No heating at all | Thermostat setting, boiler power, low pressure, boiler fault | Check thermostat, boiler display, power supply, and pressure gauge |
| Heating not working but hot water is fine | Programmer, thermostat, motorised valve, pump, or circulation issue | Check heating schedule and thermostat settings |
| Some rooms warm, others cold | Radiators need bleeding, balancing, or circulation is poor | Check affected radiators and valve positions |
| Radiators cold at the top | Trapped air | Bleed the radiator if you are confident doing so |
| Radiators cold at the bottom | Sludge, debris, or poor water flow | Consider whether a central heating chemical flush may be needed |
| One radiator not heating | Stuck valve, trapped air, balancing issue, or local blockage | Check the radiator valves and bleed the radiator |
| Boiler pressure keeps dropping | Leak, expansion vessel issue, pressure relief valve fault | Check whether pressure falls repeatedly after topping up |
| Boiler or radiators making noises | Air, limescale, sludge, pump issue, or kettling | Note the sound and where it is coming from |
| Thermostat not responding | Flat batteries, incorrect settings, poor placement, connection issue | Check batteries, target temperature, and timer schedule |
| Heating comes on at the wrong time | Programmer or smart thermostat schedule issue | Review heating schedule and time settings |
If basic checks do not solve the issue, avoid removing the boiler casing or attempting gas-related repairs. Call a Gas Safe engineer. Aren Heating & Plumbing can help with boiler repair and heating faults in South London. You can also call 0203 807 5817 or use our contact form.
Central Heating Not Working – Step-by-Step Checks
If your central heating is not working, work through these checks in order. They can help you rule out the most common causes before booking a repair.
- Check the thermostat is asking for heat
Make sure the thermostat is on, set to heating mode, and turned up above the current room temperature. If the room is already warmer than the target temperature, the heating may not come on. - Check the timer or programmer
Make sure the heating is scheduled to be on. If there has been a power cut, the timer may have reset. - Replace thermostat batteries if needed
Wireless thermostats can stop communicating with the boiler when the batteries are low or flat. - Check the boiler has power
Look at the boiler display and check the fused spur or switch near the boiler. If other electrics are off, check whether a trip switch has activated. - Check the boiler pressure
Many sealed systems work best at around 1 to 1.5 bar when cold, but always follow your boiler manufacturer’s guidance. If pressure is too low, the boiler may not fire for heating. - Look for a fault code
If your boiler shows a fault code, write it down before resetting the boiler or calling an engineer. The code can help identify the heating problem faster. - Check whether hot water still works
If you have hot water but no heating, the issue may be with the thermostat, programmer, motorised valve, pump, or heating circuit rather than the whole boiler. - Check whether the issue affects every radiator
If all radiators are cold, the issue is more likely to be boiler, thermostat, pump, pressure, or circulation related. If only one radiator is cold, the problem may be local to that radiator. - Bleed radiators if they are cold at the top
Trapped air can stop hot water circulating through the radiator properly. Bleed radiators only if you are comfortable doing so, and check boiler pressure afterwards. - Call a heating engineer if the issue continues
If your central heating is still not working after these checks, or your boiler keeps locking out, book a professional diagnosis. Call Aren Heating & Plumbing on 0203 807 5817 or request help through our contact page.
Central Heating and Radiator Problems Explained
Most central heating problems fall into a few clear categories: no heat, uneven heat, cold radiators, boiler pressure issues, thermostat faults, noisy systems, or valve problems. The sections below explain what each symptom usually means and what you can do next.
No Heat Coming Through?
If no heat is coming through at all, start with the basics. Check that your thermostat is set high enough, your timer is on, and your boiler has power. It sounds obvious, but a surprising number of heating problems come down to settings, schedules, or the thermostat not calling for heat.
If the boiler is switched on but nothing is happening, check the pressure gauge. Low pressure can stop the system from firing properly. You may also see a fault code on the boiler display, which can help identify what has gone wrong.
If your central heating is not working after these checks, do not remove the boiler casing or try to repair internal boiler parts yourself. For safe diagnosis, contact a Gas Safe engineer. Aren Heating & Plumbing provides boiler repair and heating support in South London.
Some Rooms Are Toasty, Others Freezing
If one room heats up nicely but another stays cold, the problem may be with radiator balance, trapped air, or poor circulation. This is common in homes where radiators have been adjusted over time or where the system has not been balanced properly.
A radiator that is partly warm and partly cold may need bleeding. If radiators furthest from the boiler take a long time to warm up, the system may need balancing so hot water is distributed more evenly.
If several rooms are affected, or the same radiators keep underperforming, there may be sludge or circulation issues inside the system. A professional inspection can confirm whether balancing, valve work, or flushing is the best fix.
Radiators Cold at the Top or Bottom
Radiators that are cold at the top usually have air trapped inside. Bleeding the radiator can release the air and allow hot water to fill the radiator properly again. After bleeding, check your boiler pressure, as releasing air can cause the pressure to drop slightly.
Radiators that are cold at the bottom often point to a different issue. Sludge, rust, and debris can settle at the bottom of radiators, restricting the flow of hot water. This can make the system less efficient and leave rooms feeling colder than they should.
If several radiators are cold at the bottom, a central heating chemical flush may help clear sludge and restore circulation. For a deeper explanation, read our complete guide to boiler chemical flushing.
Strange Noises Coming from the Boiler or Radiators
Banging, gurgling, whistling, or humming noises should not be ignored, especially if they are new or getting louder. These sounds can be caused by trapped air, limescale, sludge, pump problems, or water not moving through the system properly.
Gurgling often suggests air in the system. Banging or knocking can sometimes be linked to pipe movement, overheating, or circulation issues. Whistling from a boiler may be a sign of kettling, which can happen when limescale or sludge restricts water flow through the heat exchanger.
If your boiler is making persistent or sudden noises, book a professional check. Continued use without diagnosis can make some heating problems worse.
A Radiator That Won’t Heat Up
If one radiator will not heat up but the others are working, the fault is usually local to that radiator. The valve may be stuck, the radiator may need bleeding, or the system may need balancing.
Start by checking that both radiator valves are open. If the radiator is cold at the top, bleeding may help. If the radiator remains cold after that, the thermostatic radiator valve may be stuck or there may be a blockage.
If one radiator still will not heat up, our radiator repair, replacement and installation service in South London can help identify whether the issue is the valve, pipework, sludge, or the radiator itself.
Low Boiler Pressure
Low boiler pressure is one of the most common heating problems. If the pressure drops too low, the boiler may stop working or show a fault code. Many systems sit around 1 to 1.5 bar when cold, but you should always check the guidance for your specific boiler.
If pressure has dropped once, it may simply need topping up. But if the pressure keeps falling, there may be a leak, a faulty pressure relief valve, or an expansion vessel issue.
If you are repeatedly topping up your boiler pressure, arrange a professional inspection. Repeated pressure loss is a sign that something else needs attention.
Common Central Heating Thermostat Problems
Central heating thermostat problems are easy to overlook because they can look like boiler faults. If your boiler seems fine but the heating is not coming on when expected, the thermostat or heating controls may be the issue.
Common thermostat-related heating issues include:
- Incorrect temperature setting: The thermostat may be set lower than the current room temperature, so it is not asking the boiler for heat.
- Timer or schedule errors: The heating may be set to come on later, or the programme may have reset after a power cut.
- Flat batteries: Wireless thermostats often stop responding when batteries are low.
- Poor thermostat placement: A thermostat near a radiator, in direct sunlight, or in a draught can give inaccurate readings.
- Connection problems: Wireless thermostats can lose communication with the receiver near the boiler.
- Old or inaccurate controls: Older thermostats may become unreliable and fail to call for heat consistently.
If your central heating is not working but the boiler appears to have power and pressure, the thermostat should be one of the first things to check.
Your Thermostat Isn’t Playing Ball
A thermostat that is not working properly can make the whole heating system seem unreliable. You might notice the heating coming on at the wrong time, rooms not reaching the right temperature, or the boiler not responding when you turn the thermostat up.
Check the batteries if it is wireless, make sure the time and schedule are correct, and confirm that the target temperature is higher than the room temperature. If the thermostat is in a poor location, it may be reading the room incorrectly.
If your thermostat is old, inaccurate, or not communicating with the boiler, it may need repairing, recalibrating, or replacing. A modern thermostat or smart control can improve comfort and help you manage heating use more efficiently.
Valve Problems You Might Not Notice
Radiator valves can stick, seize, or stop opening properly. When that happens, hot water may not be able to flow into the radiator, even if the rest of the heating system is working.
Thermostatic radiator valves can sometimes get stuck in the closed position, especially after the heating has been off for a long period. Lockshield valves can also affect how much hot water reaches each radiator.
If a valve problem is suspected, it is best to get it checked rather than forcing it. Damaging a valve can cause leaks or make the problem worse.
If you need a radiator valve repaired or a radiator replaced, see our radiator repair and installation service.
Prevention is Better Than Repair
Many central heating problems build up gradually. Annual servicing, radiator bleeding, keeping an eye on boiler pressure, and dealing with cold spots early can all help prevent bigger heating issues later.
A well-maintained system is usually more reliable, more efficient, and less likely to break down during the colder months when you need it most.
If you are unsure whether it is cheaper to leave your heating on low or use it only when needed, read our guide: Is it better to keep heating on low all the time?
It is also worth testing your carbon monoxide alarm regularly, especially during heating season. Read our guide on how to test your carbon monoxide alarm at home.
FAQ: Common Central Heating Problems
Why is my central heating not working?
Your central heating may not be working because of low boiler pressure, incorrect thermostat settings, a timer issue, a boiler fault, trapped air, a pump issue, or a circulation problem. Start by checking the thermostat, boiler power, pressure gauge, and fault codes. If the issue continues, call a Gas Safe heating engineer.
Why is my heating not working but my hot water is?
If your hot water works but your heating does not, the issue may be with the thermostat, programmer, motorised valve, pump, or heating circuit. It does not always mean the boiler has completely failed.
Why are some radiators hot and others cold?
Uneven radiator heat is usually caused by trapped air, radiator balancing problems, stuck valves, or poor circulation. If radiators are cold at the bottom, sludge may be restricting water flow.
Why are my radiators cold at the bottom?
Radiators cold at the bottom often indicate sludge or debris inside the system. If several radiators are affected, a chemical flush for your central heating system may be needed.
Can a thermostat cause central heating not to work?
Yes. Flat batteries, incorrect settings, poor placement, timer errors, and communication faults can all stop the thermostat from calling for heat. This can make it seem as though the boiler or central heating has failed.
Why does my boiler pressure keep dropping?
Repeated pressure loss may be caused by a leak, expansion vessel fault, pressure relief valve issue, or recent radiator bleeding. If you keep needing to top up the pressure, book a professional inspection.
When should I call a heating engineer?
Call a heating engineer if your central heating is still not working after basic checks, your boiler keeps locking out, pressure keeps dropping, multiple radiators stay cold, or you hear sudden banging, whistling, or gurgling noises. For help in South London, call 0203 807 5817 or use our contact form.
Other Helpful Blogs
- The Complete Guide to Boiler Chemical Flushing
- Is It Better to Keep Heating on Low All the Time?
- How to Test Your Carbon Monoxide Alarm in Your Home
Need a Hand?
If your central heating is not working, your radiators are staying cold, or your boiler keeps losing pressure, we can help.
Aren Heating & Plumbing provides practical, reliable support for heating problems across South London. Whether you need a fault diagnosed, a radiator repaired, a chemical flush, or urgent boiler help, our team can get your heating back on track.
For fast help, call 0203 807 5817 or send an enquiry through our contact form. You can also view our plumbing and heating rates in South London before booking.
