A smelly sink is a very common problem. Over time, gunk can build up in your kitchen sink drain. Food particles then get trapped and de-composed, causing an unpleasant odour to rise up through the drain.
Leave it unattended for a few days and your kitchen will start smelling like a sewer. Read our full article about what to do to fix it.
If your boiler has been installed correctly this should not be a problem. Check out our heavy rains page for more information into the problems that can arise.
First check there is water in the cistern, if not find out why. Next check that the lever or button lifts the plunger in the siphon, in case it has become disconnected. Re-attach as needed. If you can not see what is wrong at this point it is best to call in a plumber.
Two main reasons for this problem. If your cistern does not have an external over flow pipe and the water level is too high it it over flows into the toilet so as not to flood your floor. Adjust the ball valve to lower the water level. If the valve is broken best to call a plumber. Second reason is that the syphon has an internal problem, most syphons are not very expensive so it is easier to replace one than to attempt a repair.