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Overflow Pipes & Fittings (uPVC)

High quality 21.5mm Overflow Pipe systems available in black & white. For use as condensate pipework from combi boilers.

More Information on Overflow Pipe and Fittings

Sometimes known as condensate pipe - in boilers, a small siphon is contained by the condensate trap  until it fills up to a level where the siphon is activated condensate is collected in the trap and the trap drains itself.

Condensate flows through the pipe in bursts of a few hundred millilitres at one time, which may be heard trickling through the pipe. The release of small amounts of water through the pipe is preferable to a flow, as a continuous drip is more liable to freeze.

Additionally, short bursts of hot condensate will thaw any ice which has started to form from the pipe. Just like the water at the U-bend of a sink stops smells from travelling the sewer up into the house, the condensate trap utilises some of water to prevent toxic fumes from being expelled into the sewer. Although this amount may vary depending on the design and capacity of boiler,

A condensing boiler will produce 2-3 litres of condensate per hour of operation. The provision must be made for this waste water to be discharged into an internal soil stack or waste pipe, or in an soil stack, gully, or soak-away. Water vapour from the combustion process is channelled through the boiler (along with other gases in the combustion chamber) until so much heat is drawn out of it that it condenses back into water. (In a non-condensing boiler, this procedure is absent -- the hot gases are just expelled from the flue and the heat is wasted.)

Before it's discharged into the sewer through the overflow condensate pipe, waste water -- or condensate as it's known -- is collected from the condensate trap. The overflow pipe is a condensate pipe through which a condensing boiler discharges waste water in the condensing process into the sewer. As metal pipework cannot be used, it is often readily identifiable as the plastic overflow pipe connected to the boiler.

The overflow pipe has to be plastic -- usually solvent-weld fittings -- and at least 22 mm in diameter. Copper or steel pipework cannot be used. This is because, at a pH of 3-4, the condensate is slightly acidic, and metal-based piping would be vulnerable to corrosion. The pipe must also have as few bends as possible. This is in order to prevent the condensate from becoming trapped in the overflow pipe. Condensate/Overflow pipes which are out or run through an unheated outbuilding, such as a garage, must be insulated lagging in order to prevent them from freezing and should not be longer. Where it's undesirable to insulate the pipe for aesthetic reasons, 32 mm piping will significantly decrease the chance of freezing. The up-sizing of 22 mm to 32 mm pipe should ideally be produced inside the property so that water cannot freeze in a 22 millimetre section that's outside or inside a wall cavity. The gradient should also prevent water from sitting in the pipe and possibly freezing.

Among the most common overflow pipe problems is that the water freezes blocking the pipe. The boiler's built-in detectors will detect it can't release the condensate, and will prevent the boiler from lighting, leaving the household. If a condensate pipe is suspected, this can be remedied by pouring water on the exposed section of pipe, or by putting a hot water bottle. Click here to see more information on this subject, including how to prevent it from freezing in future. Other obstructions in the condensate pipe may include sewage, which has travelled up the pipe due to a poorly configured waste water system at the building. In some cases that are very bad, the sewage may travel far back up the pipe to overwhelm the boiler.