What Rotorua air does to a heat pump
Copper goes first
BRANZ's 2018 bulletin on geothermal environments found copper the most vulnerable metal in Rotorua, with heavy corrosion even in areas where hydrogen sulphide was low.
Worst near Sulphur Bay
Copper samples near Sulphur Bay lost between 443 and 495 g/m2 in a single year. BRANZ says the land 200 to 400 m south or southwest of the bay could be classed CX, the extreme corrosivity category.
A long heating season
Rotorua Airport averages 19.9 air frosts a year, and NIWA gives Rotorua Aero AWS 2,033 heating degree-days. A unit heating through that runs hard for months, on top of what the air is doing to it.
How often in Rotorua
Mitsubishi Electric NZ sets at least yearly for standard home systems and says geothermal systems may need more. BRANZ suggests a service check every 2 to 3 years in general, but we wouldn't stretch that far in geothermal air.
Your warranty may set the floor anyway. Gree NZ's warranty card is void if maintenance goes past 12 months, and Rinnai NZ wants yearly maintenance by its own authorised service centre. Our national servicing page lists what other brands ask.
What a geothermal service should cover
The outdoor coil and fins
Cleaned, then checked closely for corrosion along the fins and coil ends, not just given a rinse.
Copper pipe connections
Copper is what BRANZ found most at risk, so the exposed refrigerant pipe connections at the outdoor unit deserve a close look.
Protective coatings
Any coating applied at install inspected and renewed if the brand needs it. Mitsubishi Electric NZ makes maintaining applied corrosion protection an owner responsibility, and Black Diamond Technologies only covers corrosion damage where its own Nyalic protection was applied and kept up.
Paint and casing
Damaged paint touched up before rust gets a hold. Temperzone's yearly maintenance list for Hitachi systems includes it.
Indoor filters, coil and drain
The standard service tasks. Mitsubishi Electric NZ says servicing clears dust and contaminants from coils and drain trays.
A written record
Dated, with notes or photos of any corrosion, so you can compare year to year and show the warranty company if you need to.
What makes a Rotorua service bigger or smaller
Where you are. BRANZ found heavy copper corrosion even where hydrogen sulphide was low, so don't assume a unit across town from Sulphur Bay is safe. Closer to the worst areas, expect more corrosion work.
How it was set up. A unit fitted with corrosion-resistant coils and extra coatings, as BRANZ recommends for geothermal areas, is usually a maintenance visit. A bare unit that's been through a few winters may need repair work as well.
When it was last done. The longer corrosion goes unchecked, the more of the unit it can reach, so a long gap usually means a longer visit.
Ask before you book
- Do you service many heat pumps in geothermal parts of Rotorua?
- What corrosion protection does my unit have, and is it still intact?
- Will you check the refrigerant pipe connections at the outdoor unit?
- Will your report note any corrosion, so I can compare next year?
- Does my brand's warranty accept your servicing and any coating you apply?
What we'd do
What we'd do in Rotorua
We'd book a service at least once a year and ask a technician who knows geothermal air whether our address calls for more. We'd want every visit to end with a written note on corrosion, so small damage gets dealt with before it reaches the copper pipework. And if the unit was never protected, we'd ask what adding protection now would involve.