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

The Christchurch City Council’s view on hot water cylinder failure and a rebuttal by Superheat


What causes hot water cylinders to fail?

Christchurch has historically had issues with hot water cylinder failure. Certain areas of the city, such as Cashmere, have been affected more than others.


The Christchurch City Council (CCC) has never acknowledged the high rate of element failures and hot water cylinder (HWC) failures in the Cashmere area.  Now they are admitting that they know about the issues.  Superheat has undertaken many water tests and found that there are spikes in chlorine levels in areas of Cashmere – likely caused by spot chlorination.


We are still working with the industry to better understand the scale and possible causes for the increased rate of failure over recent months.


Superheat commissioned a study by the University of Canterbury to identify the most likely cause of copper HWC failure.  In the absence of a credible alternative proposition, the “Water Cylinder Corrosion Report” identified chlorination as the likely cause.  The CCC said that they would peer review the study.  They have not been able to disprove the Report.


There are multiple factors that can lead to a hot water cylinder leaking, and then needing to be replaced. These include:  the chemical composition of the water, age of the cylinder, the type of cylinder, any debris in the cylinder, and the quality and thickness of copper used.


The CCC are attempting to apportion blame to the HWC manufacturers.  Superheat, Rheem, Peter Cocks, Perkins et al meet the New Zealand Standards.  Perkins is no longer in business but Superheat, Rheem and Peter Cocks are regularly audited and carry the “S Mark” certification  The thickness and quality of the copper are some of the items that are checked.  It is wrong for the CCC insinuate that we all use poor quality or thin copper.


All the HWC manufacturers listed above source copper from different mills.  It is statistically almost impossible that copper HWC’s are failing at the same time due to poor quality or thin copper.  The most likely cause is a change in the chemical composition of the water, which in this case is the chlorination of the water.


We have been working with manufacturers and it appears the majority of the cylinders that are failing are reported as older, low pressure copper cylinders.


We have found that there are failures of HWC’s of all ages.  Are the CCC saying that it doesn’t matter if older HWC’s fail?  The homeowner still has to replace the HWC at the homeowner’s own cost.


Why don’t other parts of New Zealand, where water is chlorinated, also have high rates of hot water cylinder failure?

The chemical composition of water supplies around the country is quite different.

Places like Auckland and Wellington use surface water (from rivers and streams) which generally develops a protective film when in contact with copper plumbing. In Christchurch we are using groundwater (from aquifers).

Pitting corrosion leading to pinhole failure happens more commonly in some bore water (underground) supplies.

In Hastings and Napier, for instance, they have bore water supplies and also experienced a rise in hot water cylinder failures following chlorination of their water networks.  Napier and Hastings found the number of failing cylinders decreased over the year after chlorination was introduced.


At our meetings with the CCC they admitted that they didn’t know of the increase failure rate of HWC’s in the Havelock North, Napier & Hastings region.  Now the CCC are saying that they knew about it.  This should have been a consideration in the decision of what type of water treatment should be used.


We are continuing to monitor the situation and work with manufacturers and suppliers to gain further understanding. Work is also progressing on our well head remediation programme to reduce the chlorine levels in our water.


Have the CCC not read the Water Cylinder Corrosion Report?  The CCC have not come up with a credible alternative proposition.


Are some cylinders more suited to Christchurch conditions?

There are specific cylinders that are sold for areas where pitting corrosion is prevalent. Christchurch, particularly around the Cashmere area, has a history of hot water cylinder failures. If you are replacing your cylinder talk to your plumber about the best option for your area. Some options include enamel-lined steel or stainless steel cylinders.


Adding a chlorine filter will give the benefits of nice tasting water without chlorine as well as protecting copper HWC’s and copper pipework.


If hot water cylinders are failing, could the same happen to gas systems or pipes?

There is no evidence of an increased number of failures in copper heat exchangers in gas continuous flow units, copper water pipes or other fittings.


This statement from the CCC is untrue.  Increased rates of pinhole failures in copper pipework has been identified.



Superheat is happy to provide a copy of the Water Cylinder Corrosion Report by email.  Please contact us via our website if you want a copy.


Trevor, Managing Director