How to diagnose common central heating problems

5 things to check if you have no heating 

1. Thermostat 

Check that the thermostat hasn’t been set too low. The boiler will only work if the heating has been set higher than the room temperature. 

2. Timer 

Most heating timers have four settings: Off, On continuously, All day (sometimes called Once), and Timed, which allows the heating to come on multiple times a day. Double-check that the heating is coming on when you want it to and that you haven’t accidentally set it for 4am instead of 4pm. 

3. Pilot light 

Check your boiler for fault codes and attempt to reset the boiler using the reset button, this is usually covered in your boiler manual (or we have a handy guide). 

Older boilers may have a pilot light which could have gone out. If this is the case, your boiler manual will explain how to re-light it. 

If these measures don’t solve the problem, then call in a Gas Safe Registered engineer.

4. Boiler pressure

Look at your boiler’s pressure gauge. If it's below 1 bar, the boiler may need repressurising. If the pressure is too high (above 2.5 bars or in the red zone), then it may have switched off to prevent any further damage to the boiler. High and low pressure are a common cause of heating issues.

5. Condensate pipe

If it's particularly cold, your condensate pipe may have frozen. This is a common reason boilers stop working during winter. 

Common radiator issues that indicate a central heating problem

Cold radiators upstairs 

If you have a feed and expansion cistern in the loft—it could be empty. 

If the cistern is dry, gently tap the ball valve to encourage water to flow into the tank. The water should rise just enough to lift the ball valve. Don’t overfill the tank, as there must be room for the water to expand. 

Once the cistern has filled, you‘ll need to bleed the affected radiators. Check the overflow for the next couple of days to ensure the ball valve is working correctly. If it’s dripping, get in touch with a professional plumber to check and replace as necessary. 

If you don’t have a feed and expansion system, it’s time to call a heating engineer.  

Cold radiators downstairs 

If your downstairs radiators are failing to heat up, then try turning the upstairs radiators off using the radiator valves. If the problem continues, then there’s a good chance your pump is broken or on its way out, and there may be air in the system (an “air lock”). You’ll need to call in a plumber to fix this. 

Remember, cold radiators could lead to frozen or burst pipes in winter, so they need to be tackled quickly. 

The top of the radiator is cold 

This likely means there’s air in the system, so you’ll need to bleed the radiator to release the trapped air. 

The middle of the radiator is cold 

This may mean a build-up of rust or sludge is obstructing the flow of water through the radiator. Use a central heating system cleaner appropriate for your system type (open vented or sealed). Cleaning your heating system can be a big job, so if in doubt, get a professional plumber out. 

Leaking radiator 

When you have one or more leaking radiators, there are some actions you can take before the problem escalates. A pinhole leak on a radiator can be a sign of internal corrosion. This can happen when debris that collects during installation isn’t properly removed (and this can be within weeks of a system being fitted) or because of air being drawn into the system.

To fix the problem, try the following: 

1. Shut off your boiler and let it cool. 
2. Place a bowl and a dustsheet under the leak. Plastic bags can also be used to direct the flow. 
3. Turn off the valves at each end of the radiator to relieve pressure. 
4. Drain the radiator down. 
5. Remove the radiator and leave the rest of the system running. If in doubt, get a professional plumber. 
6. Flush out the system using a non-acidic cleaner. 
7. Refit the radiator.

Air locks in the central heating system 

In some cases, it’s likely there’s air in the system and not just an individual radiator. You can tell when this is happening because some or all your radiators may be cold when the heating is on. 

How to troubleshoot airlocks in your central heating 

• Start by bleeding all the radiators in the house, not just the cold ones. This can help release any air trapped in the pipes or radiators. 
• If some radiators are still cold, partially close the lockshield valves on the radiators that heat up quickly. This will help to redirect hot water to radiators that are slower to warm up.

Leaking pipes 

Leaky pipes are a nuisance and can grow into bigger problems if left unchecked. 

Leaky connection or joint 

If water is leaking from a connection or joint, then it should be easy to tighten the joint with a spanner or wrench. However, if the joint has been soldered, you won’t be able to tighten it, and the pipe may need replacing. 

Leaking from the pipe 

If the pipe is leaking from a section that has no joint or connection, then the pipe will need to be replaced. A short-term solution is to tie a rag around the pipe or use specialist sealant from a DIY store. You may wish to get a professional plumber to replace the pipe, as it can be a messy and complex job. 

Noisy boiler 

If your boiler makes all sorts of odd banging and bumping noises, then there may be a lack of water in the feed and expansion tank. This is usually located in the loft, or if you have a sealed system, it may need repressurising. The gauge should read 1 bar minimum. 

Another issue could be a build-up of sludge and scale in your boiler. Air in the boiler can also cause similar banging noises. Don’t try to tackle these problems yourself, call in a Gas Safe Registered professional heating engineer. 

Water gurgling 

Water gurgling noisily through the central heating system is a pretty clear sign that you have air in the radiators. This problem can be easily resolved by bleeding your radiators. 

The boiler keeps switching off 

If your boiler turns off repeatedly, checking for a fault code on your boiler display is a good place to start. The boiler could be switching off for several reasons and knowing your fault codes will give you a better idea of what’s wrong.  

Potential problems could include: 

• High or low boiler pressure. 
• A frozen condensate pipe (if it’s cold outside). 
• Trapped air in the system. 

However, it could also be the result of more complicated problems such as: 

• A faulty thermostat. 
• Faulty pump. 
• Internal sensor problems. 

In this case, it’s best to call a Gas Safe Registered engineer to inspect and repair the system. If you’re having trouble diagnosing the problem, your boiler manual will contain a list of fault codes and what they mean.  

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Book a trusted, Gas Safe Registered engineer in just a few clicks, at time that suits you. You’ll always get clear, upfront pricing so no need to worry about any hidden costs. Whether it’s a big issue or a quick fix, our expert repair team at Ding is on hand to get things back to normal without the hassle.