When water is heated it expands, this is called thermal expansion. When heated from cold the volume of water can increase by as much as 3%. For a 180L hot water cylinder (HWC) this could be as much as 5.4 litres. HWCs are designed to relieve expanded hot water through an open vent pipe on the roof or by way of a relief valve and pipe to an outside wall or drain. There have been a number of cases where these vent/relief pipes have been blocked off by owners trying to stop the dripping. In some cases, where a secondary safety vacuum break was not fitted, the water cylinder has exploded with devastating consequences. Walls and roofs have been blown off and houses moved on their foundations. These days’ cold water relief valves are installed to the inlet side of the HWC to save hot water.

To test whether the dripping relief pipe is normal expansion or a faulty valve:

– turn off the power supply to the tank for 5 minutes.
– if the dripping stops then this is normal thermal expansion.
– if it continues then the valves are probably faulty.

No. Hot water must be stored over 60 degrees Celsius to prevent the growth of legionella bacteria in the hot water tank. A tempering valve is fitted to the hot water outlet to lower the temperature to 55 degrees C.

The Building Code requires that the temperature of hot water delivered to sanitary fixtures used for personal hygiene purposes such as showers, baths and basins shall not exceed 45 degrees C for old people’s homes, schools and early childhood centers and 55 degrees C for all other buildings.

I do sympathise with your plumber. There are so many different brands on the market these days, that unless the customer knows from whom the tap was purchased or what the brand is, it may be very difficult to locate parts. So many unmarked brands are coming from Asia and Europe by the crate load and dumped on the market that spare parts really do become and issue. So I would suggest that if you purchase any tapware, buy from a credible source, keep all receipts and documents especially if the tap does not have the manufacturers stamp on it.

Unfortunately some cheap imported tapware is very basic with a high lead content. When you purchase a tap feel the weight of it compared to domestic taps. If it feels heavy it may have a very high lead content which can leach into the water supply when the tap is off. This is not good for your family’s health and the tap may not last the distance. If the tap is not stamped with the manufacturers name then make sure you buy parts from the supplier for future maintenance. Note the name of manufacturer and the reseller so that the plumber can source parts when repairing the tap in the future.

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