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At M.J. Robertson Plumbers we get a lot of enquiries about poor hot water pressure and lousy showers.

Most older homes have a low pressure hot water system where the hot water pressure is only about 10 to 50kpa, this is a bit like having the water fall from one to five metres above you whereas a mains pressure water supply is like having the water fall from around 50 metres above you!

Most modern tapware is designed for mains pressure systems and although some state “suitable for all pressures” they don’t always work that well on low pressure systems.

We often recommend to our clients to convert to mains hot water especially if their existing hot water system is over 20 years old, in most cases this is quite a straightforward job as we usually only have to remove the existing hot water cylinder and install a new mains option.  Sometimes, however, the shower mixer needs to be altered or replaced to match the new mains pressure system.

The existing pipework is usually fine and would only leak if it, or one of its joints, was in poor condition in the first place.



Our most preferred option is an instant continuous flow gas hot water system.

For most houses you will find:

  • It is easy to install on the outside of your home
  • Frees up space inside where the old cylinder was installed
  • Cheaper to run than stored mains hot water system
  • Never run out of hot water (put the whole rugby team through the shower!)
  • When you’re away it doesn’t cost anything to run
  • Earthquake proof as there is very little weight in the system
  • No building consent needed as Gasfitters are self-certifying

Most people aren’t too keen on a gas system at first but once it’s up and running people love them and you can see some of the benefits above.


Mains pressure storage hot water cylinders.

These systems have been used successfully for many years and are fine but do have some draw backs when compared to instantaneous gas hot water.

  • You have to keep 200 to 300 litres of water hot all of the time
  • A 300 litre mains pressure cylinder full of water can weigh around 400kg! (that’s more than the All Black’s front row)
  • Also are very large, with a diameter of 600mm and they are around two metres tall.
  • There are a list of valves need to regulate the water in and out of the cylinder
  • If you use all the water you have to wait for it to heat again (rugby team not happy!)
  • A building consent may also be required to install a valve vented hot water system.

Still not a bad system and we are now installing some on the outside of the house to free up room inside, plus it makes them much easier to service when needed.


Solar hot water is a fantastic option if you live in a warm climate and don’t have to contend with an OHS working at heights policy!

In Christchurch we wouldn’t recommend solar to any of our clients due to our low sunshine hours through half of the year, and a good quality known brand solar system is also very expensive.

We know there are a lot of cheaper systems on offer but anybody can import a solar system and sell it easily these days, but are parts, back up and service available in say five years time?

This along with the OHS working at heights laws, the less things on your roof the better as up-keep and servicing is just getting too expensive.


Air to water heat pumps.

This is still quite new to New Zealand but we do believe in the years to come this will be one of the main hot water heating systems in the country, in the same way home heating heat pumps have taken over a lot of the house space heating here.

As with most heat pump systems you get an average 3KW of heating for every 1KW you put in, making them very efficient.

Drawbacks could include a slow recovery time in cold climates and the need for an electrical element back up through the coldest months of the year.

Both solar and heat pump systems usually run through a larger type (200 to 300 litre) mains pressure storage hot water cylinder with the same set up as mentioned above.


These are rough estimates to give you an idea on supply and costs of these systems using only top of the line products backed by New Zealand companies and warranties.


Instantaneous gas                           $2,800 - $4,000 plus G.S.T

Mains storage cylinder                  $3,000 - $4,200 plus G.S.T

Solar indirect for cold climates    $9,000 - $14,000 plus G.S.T.

Air to water heat pumps               $6,000 - $8,000 plus G.S.T.

All these prices are exclusive of any electrical costs.