If you are concerned that your flue pipe is leaking gases back into your home, then you need to do a simple test in order to check this out. You may be concerned about a strange smell when your water heater is working, or you may find that your carbon monoxide alarm sounds. Checking that the flue pipe is not leaking will help to put your mind at rest, and if it is leaking, then you can get it fixed straight away.
Step 1 - Open the Heater
Turn off your mains water supply, and then drain the water heater using the drain valve at the bottom of the tank. You should make sure that the water is as low as possible, and then open up the top of the heater. You should be able to locate the flue pipe easily.
Step 2 - Test the Flue Pipe
Start the fan, if you have one, and then light an incense stick, and pass it close to the flue pipe. Watch the smoke as it gets drawn in. You may find that smoke emerges from close to the pipe, or is simply taken up by the device. Whatever happens, you should make a note of where the smoke ends up.