Your continuous flow (instantaneous) hot water unit is displaying an error code because its built-in diagnostic system has detected a fault — anything from a simple ignition hiccup to a more serious gas pressure or venting issue. Many faults are minor and easy to resolve yourself, but some require a licensed gasfitter to diagnose and repair safely.
What Error Codes Actually Mean
Continuous flow units from brands like Rinnai, Rheem, Bosch, and Paloma all use numeric or alphanumeric error codes to pinpoint problems. The exact meaning of each code varies by brand and model, so your first step is always to check your unit's manual. If you've misplaced it, most manufacturers publish manuals on their websites or you can search by model number.
That said, certain fault categories are common across most brands:
| Code Category | Typical Cause | DIY Friendly? |
|---|---|---|
| Ignition failure | No spark or flame not detected | Sometimes |
| Flame loss / extinguished | Wind, gas supply issue | Sometimes |
| Overheating / high temp | Blocked heat exchanger or low flow | Rarely |
| Exhaust / flue fault | Blocked flue or fan failure | No — call a gasfitter |
| Gas valve fault | Internal component failure | No — call a gasfitter |
| Water flow too low | Blocked filter or low pressure | Yes |
| Sensor fault | Temperature or pressure sensor failure | No — call a gasfitter |
Common Causes and What to Check First
Before calling anyone, run through these basic checks:
1. Gas Supply
- Check that other gas appliances in your home (hob, oven) are working. If they're not, your LPG bottle may be empty or there could be a mains gas supply interruption — contact your gas retailer.
- If you're on LPG, make sure the cylinder valve is fully open.
2. Power Supply
- Continuous flow units need electricity to operate the igniter, fan, and controls. Check the unit is plugged in or that the circuit breaker hasn't tripped.
3. Water Flow Rate
- Most units require a minimum flow rate (often around 2–3 litres per minute) to activate. Check that taps are open sufficiently and that the inlet filter screen isn't blocked with sediment. This small filter is usually located where the cold water supply enters the unit and can be cleaned by a homeowner.
4. Flue and Ventilation
- Check that nothing is blocking the flue outlet outside — bird nests, leaves, or debris can trigger flue fault codes. Do not attempt to dismantle the flue yourself. If you suspect a blockage, call a licensed gasfitter.
5. Reset the Unit
- After addressing any obvious issue, try a power reset: turn the unit off at the isolating switch or unplug it, wait 30 seconds, then restart. Some transient faults (like a wind-induced flame loss) will clear on their own.
Gas Work Is Restricted — Know the Rules
In New Zealand, work on gas appliances and fittings is restricted work under the Gas Act 1992 and associated regulations. This means that any repair, adjustment, or replacement involving gas components — including gas valves, burners, heat exchangers, or gas connections — must be carried out by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB).
As a homeowner, you are legally permitted to:
- Turn the gas supply on or off at the meter or cylinder valve
- Clean the water inlet filter
- Reset the unit after a transient fault
- Replace batteries (on battery-ignition models)
You are not permitted to open the unit casing, adjust burners, replace gas components, or modify the flue system. Doing so is illegal, could void your warranty, and — most importantly — poses a serious risk of gas leak, fire, or carbon monoxide poisoning.
Safety note: If you smell gas at any point, do not attempt to reset or operate the unit. Turn off the gas supply at the meter or cylinder, ventilate the area, avoid using electrical switches, and call your gas retailer or a licensed gasfitter immediately. For emergencies, call 111.
NZ Building Code Considerations
Continuous flow hot water units must comply with relevant NZ Building Code clauses, including G12 (Water Supplies), as well as applicable gas installation standards, as well as relevant gas installation standards. If your unit is being replaced rather than repaired, a building consent may be required — though some like-for-like replacements may qualify as Schedule 1 exempt work. Always confirm with your local council before proceeding, and ensure any installation is carried out by a licensed gasfitter. More guidance is available from MBIE Building Performance.
When to Call a Professional
Call a licensed gasfitter if:
- The error code relates to a gas valve, burner, or sensor fault
- The unit repeatedly throws the same code after resetting
- You suspect a flue blockage or exhaust fan failure
- You can smell gas near the unit
- The unit is more than 10–15 years old and faults are becoming frequent (replacement may be more cost-effective)
- You're unsure of the cause — guessing with gas appliances is never worth the risk
You can find qualified, local gasfitters on tradedirectory.co.nz. Always ask to see their current PGDB licence before work begins.
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