As parts of the UK prepare for the coldest winter weather in recent years, condensing boilers which produce water as a by product become more at risk of breaking down if temperatures remain at sub zero for a prolonged period of time. If the boiler stops and a gurgling noise is heard then a blocked condensate pipe may be a cause especially if the temperature is negative and the pipe goes to an external drain. The boiler buoy can give a simple indication that this is the problem and has a easy to operate tap to bypass the blockage and allow the boiler to restart.