Waiting at the tap while cold water runs down the drain is frustrating — and surprisingly common with gas hot water systems in New Zealand homes. The good news is that most delays have a straightforward cause, and some can be fixed without calling a tradesperson. Here's what's likely going on and what you can do about it.
The Most Common Reason: Distance from the Unit
The single biggest cause of slow hot water delivery is simply pipe distance. Hot water sitting in the pipes between your gas unit and the tap cools down over time. When you turn on the tap, all that cooled water has to flush out before the hot water arrives. The longer the pipe run, the longer you wait.
This is especially common in:
- Older NZ homes where the hot water unit is located in a garage, laundry, or outside — far from bathrooms and kitchens
- Two-storey homes where the unit is on the ground floor and bathrooms are upstairs
- Homes with large-diameter hot water pipes (more volume to flush)
Your Pipes Are Losing Heat
Even a short pipe run can cause delays if the pipes are uninsulated. In cooler parts of New Zealand — think Southland, Canterbury, or Central Otago — uninsulated pipes in subfloor spaces or exterior walls lose heat rapidly between uses. Wrapping exposed hot water pipes in foam pipe lagging (available at Bunnings or Mitre 10) is a simple DIY job that can noticeably reduce wait times and save energy.
Continuous Flow (Instantaneous) vs Storage Units
If you have a continuous flow (instantaneous) gas unit, there's an additional factor: these units take a moment to fire up and reach temperature. Most modern units ignite within a second or two, but some older or lower-quality units have a longer ignition delay. You may also notice a brief burst of cold water — sometimes called a "cold sandwich" — if you turn the hot tap on and off quickly, because the unit shuts down between uses.
Storage gas hot water cylinders don't have this ignition delay, but they still suffer from the pipe-distance issue described above.
Low Flow Rate at the Tap
A low flow rate means it takes longer for the hot water to push the cold water out of the pipes. Check whether your tap aerators or showerheads are partially blocked with limescale or debris — this is common in areas with harder water. Cleaning or replacing aerators is a simple DIY task.
Also check your home's mains water pressure. Low pressure (below around 350 kPa) can affect how quickly hot water travels through the system. Your local council or a plumber can advise on typical pressure in your area.
Unit Temperature Setting
If your gas unit's temperature is set too low, the water may not feel hot enough at the tap even when it arrives — leading you to run it longer. As a guide, MBIE Building Performance and the Healthy Homes standards recommend hot water be delivered at a safe temperature (typically 55°C or above at the unit to prevent Legionella, but no hotter than 55°C at accessible taps to prevent scalding). Adjusting the temperature setting on a gas unit is restricted work — see below.
Scale or Sediment Build-Up
Over time, scale and sediment can build up inside the heat exchanger of a continuous flow unit, reducing efficiency and slowing heating. This is more common in hard-water areas. A licensed gasfitter can flush and service the unit — most manufacturers recommend a service every 1–2 years.
Solutions Worth Considering
| Solution | DIY or Trade? | Approximate Cost Guide |
|---|---|---|
| Insulate exposed hot water pipes | DIY | Low (materials only) |
| Clean tap aerators / showerheads | DIY | Minimal |
| Install a hot water recirculation pump | Licensed plumber/gasfitter | Moderate |
| Relocate the hot water unit closer to bathrooms | Licensed gasfitter + LBP | Higher |
| Service / descale the unit | Licensed gasfitter | Moderate |
| Upgrade to a higher-capacity or better-positioned unit | Licensed gasfitter | Higher |
A hot water recirculation system is one of the most effective long-term fixes — it keeps hot water circulating in the pipes so it's ready almost instantly at the tap. However, installation involves work on the gas appliance and pipework, so it must be carried out by a licensed professional.
When to Call a Professional
Some tasks related to your gas hot water system are legally restricted work in New Zealand and must only be carried out by a gasfitter licensed by the Plumbers, Gasfitters and Drainlayers Board (PGDB). This includes:
- Adjusting the gas pressure or burner settings on the unit
- Changing the temperature controller or thermostat
- Any work on the gas pipework or connections
- Installing, relocating, or replacing the hot water unit
- Servicing the heat exchanger or burner assembly
Safety note: Never attempt to modify or repair the gas components of your hot water unit yourself. Gas leaks can cause fires, explosions, and carbon monoxide poisoning. If you smell gas, turn off the supply at the meter, ventilate the area, and call a licensed gasfitter immediately.
For plumbing work on the water side (such as fitting a recirculation pump or replacing pipework), you'll need a licensed plumber. You can find qualified local gasfitters and plumbers on tradedirectory.co.nz.