Blogs from the team at Superheat



Is this the end…?


Is this the end for hot water storage cylinders?  Archaic dinosaurs heated by fossil fuels….


The future is the emerging technologies that are becoming mainstream. Imagine a home or a business heating hot water with a hot water heat pump giving three times the efficiency of electric resistance elements.  Then add photovoltaic panels generating power from your rooftop.


These technologies are now real and affordable. But what other technology is needed? The old fashioned hot water storage cylinder! Think of it as a battery storing energy (hot water) for when you need it.  And at a fraction of the cost of gas water heating.


Be prepared for the revolution and specify a Superheat hot water heat pump ready hot water cylinder.

Trevor, Managing Director

Failure of copper hot water cylinder in Christchurch 2018


Christchurch residents have experienced unprecedented failures of copper hot water cylinders (HWC) from July this year.  These failures are happening to all copper HWC models from all manufacturers of copper low pressure hot water cylinders.


As a background to the Christchurch events, an outbreak of gastroenteritis occurred in Havelock North in August 2016 when 5,500 of the town’s 14,000 residents were estimated to have become ill with campylobacteriosis.  Two bores were identified as the source of the contamination in Havelock North.  As a result of this Havelock North and Hastings bores were treated by chlorination of the water supply.  An unforeseen consequence of the chlorination of the drinking water supply has been the high levels of failure of copper HWC’s and pitting of copper pipework.


Both Havelock North / Hastings and Christchurch water supplies are drawn from underground aquifers when most other towns and cities in New Zealand have large reservoirs.  Sunlight will dissipate chlorine in treated water in a large reservoir reducing high concentrations of chlorine.


In late March 2018 the Christchurch City Council commenced chlorination of the city drinking water supply and significant numbers of copper HWC’s started to fail from July 2018 onwards.  The most common cause of failure is pinhole corrosion in the bottom dome of the HWC.  This corrosion is otherwise referred to as pitting and presents itself as a jade green lump on the inside of the bottom dome of the HWC and a neatly drilled hole looking from the outside of the HWC.


Superheat, Rheem and Rinnai are working together with the Christchurch City Council to identify the cause of the failure of copper HWC’s and the failure of elements in stainless steel hot water cylinders.  It is likely that the change in the water chemistry is responsible for the pitting and failure of the hot HWC’s and may in future result in pinhole corrosion in copper pipework.  This prognosis will be investigated and reported.

Trevor, Managing Director

Investigation into the cause of failure of copper hot water cylinders in Christchurch 2018


Superheat commissioned an investigation by the University of Canterbury into the failure of copper hot water cylinders (HWC’s) in Christchurch following the chlorination of the Christchurch water supply. The investigation was led by Professor Milo Kral, a respected authority in corrosion study.

Forty failed copper HWC’s were inspected using an Endoscope camera. The camera showed signs of pitting in the bottom dome of all the inspected HWC’s. Four HWC’s were selected for further testing by Professor Kral’s team. The selected four HWC’s represented a range of ages, manufacturer’s and geographic locations in the City.

The report “Copper Hot Water Cylinder Corrosion Analysis” identified the following points.

  • The research found that all the tested HWC’s failed due to leaks caused by pitting corrosion. Pitting corrosion is a localised form of corrosion characterised by cavities or holes in the affected material.
  • The HWC’s tested all had multiple corrosion pits and there was no difference in the pitting behaviour between any of the HWC’s tested.
  • The pitting occurred most often in regions of the HWC bottom dome with the largest sediment deposits.
  • EDS (Energy Dispersive X-Ray Spectroscopy) analysis detected chlorine in the corrosion products of all pitting sites.
  • Chlorine was detected only at the pit locations and not on other surfaces.
  • EDS analysis showed the presence of iron oxide in corrosion products on all tested HWC’s.

The report concluded that the pitting observed was most likely due to the presence of chlorine and was influenced by the presence of iron in the sediments that settled to the bottom of the cylinders.

My view is that in the absence of a credible alternative proposition, the chlorination of the Christchurch water supply by the Christchurch City Council has caused the failure of copper hot water cylinders.

Trevor, Managing Director