Hot water cylinder manufacturers fed up with the mysteriously high rate of copper hot water cylinder failures in Hastings are no longer offering warranties.
Hastings District council, plumbers and manufacturers have still not found a definitive reason why Hastings has the highest rate of hot water cylinder failures in the country.
Sales of replacement cylinders in Hastings postcodes 4120 and 4122 have more than trebled since 2016 and warranty claims have increased a similar amount in the same time period.
The area represents 34 per cent of nationwide LPCU failures and warranty claims, by far the highest in the country.
The affected areas include Flaxmere, Saint Leonards, Mahora, Raureka, Mahora, Camberley, Tomoana, Longlands, Frimley, Woolwich, Parkvale, Akina and Mayfair.
Manufacturer Rheem added a warranty exclusion in March for any of its low-pressure copper hot water cylinders (LPCU) installed in the Hastings District postcodes 4120 and 4122.
The exclusion applies to cylinders that have been installed from April 1, 2022 onward.
The Rheem warranty guide cites localised water conditions causing pinhole corrosion as the reason for the exclusion.
Master Plumbers chief executive Greg Wallace estimates Rheem supplies 70 to 80 per cent of the market.
Hastings-based owners of Rinnai cylinders bought since 2020 may be in jeopardy as well.
Rinnai gives a limit of between -1.0 and 0.8 for the Langelier Saturation Index (LSI), but water sampled by HDC from Hastings West and Flaxmere is very close to or below -1.0 as of testing in April 2022 and has been at a similar level as far back as October 2018.
LSI is an approximation calculated from several factors that measure the calcium carbonate scale-forming and scale-dissolving tendencies of water.
At levels, less than 0 the water tends to be corrosive to calcium carbonate protective coating.
Wallace said that while Rinnai had not made explicit postcode exceptions yet he understood that they were looking to possibly do so for the area soon.
He said Master plumbers planned to bring the issue of the high rate of LPCU failures in the area to water regulator Taumata Arowai.
Hastings District Council group manager asset management Craig Thew said the council complies with NZ Drinking Water Standards. LSI is just one of several factors that could affect the cylinders.
"The manufacturer's range will be conservative and consumers would expect that a cylinder will perform equally as well at -0.9 as it would at -1.0.
"The issue is that very premature failures of low-pressure copper cylinders and elements are occurring that may not be explained by water chemistry alone."
He said investigations are ongoing and the council is awaiting advice from an independent specialist.
"Once we have a more comprehensive understanding, we will be in an informed position to enable the council to consider what further solutions may be appropriate."
Hastings-based Peak Plumbing & Gas Ltd owner Grayson Allen said other factors besides water chemistry could include other parts of the piping infrastructure or less heavy metals used in manufacturing plumbing.
He said plumbers had been given notice by Rheem that the two postcodes would be excluded from the warranty.
He said it was likely other manufacturers would soon follow suit.
He said stickers on LPCU sold by merchants notifying consumers that the warranty would be void within those postcodes and plumbers would give notice too.
"If I had a customer that insisted on having a copper cylinder put back in, there would be a disclaimer signed by the customer saying they take full responsibility for the warranty."
He said a postcode exclusion was not specific to Hastings and manufacturers did it to mitigate liability in areas with known issues.