Watch this video tutorial to learn how to troubleshoot central heating problems.
If you have no heat at all, check that the thermostat hasn't been set too low. The boiler will only work if the heating has been set higher than room temperature. There may also be a problem with the timer - make sure that the heating is coming on when you want it to. Finally check that the pilot light in your gas boiler hasn't gone out. If it has, there are usually instructions as to how to re-light it on the inside of the boiler door. If none of these helped, call in a professional.
Step 2: If your boiler makes odd banging and bumping noises, then there may be a lack of water in the feed and expansion tank. Take a look in your loft, where you should find the tank, and make sure that the tank is topped up with water. If not, there may be a frozen pipe, airlock or even the main water has been switched off.
If the feed and expansion tank seems OK, then another issue could be a build up of sludge and scale in your boiler. Air in the boiler can also cause similar banging noises. Call in a professional heating engineer.
If the water is leaking from a connection or joint, it can be quite easy to tighten the joint with a spanner or wrench. Be careful though. If the joint has been soldered, you won't be able to tighten it and you may need the pipe replaced.
If the pipe is leaking from a section which has no joint or connection, then the pipe will need replacing. Call out a professional to do this but as a short term fix to stop the leak, tie a rag around it or use specialist sealant from a DIY store.
If you can easily hear water gurgling through the central heating system, then it is a clear sign that you have got air in the radiators. This problem can be easily resolved by bleeding the radiators.