How to Safely Replace a Faulty Thermostat on a Storage Heater

Storage heaters are a common heating solution in many New Zealand homes, particularly in regions with off-peak electricity tariffs. If your storage heater isn't holding heat or cycling correctly, a faulty thermostat is often the culprit — but before you reach for a screwdriver, it's important to understand what work you're legally allowed to do yourself and what must be handled by a licensed electrician.

Understanding How Storage Heater Thermostats Work

Most storage heaters have two separate controls:

• Input thermostat (charge controller): Regulates how much heat the heater stores overnight during off-peak periods.
• Output thermostat: Controls how much stored heat is released into the room during the day.

When either of these thermostats fails, the heater may not charge properly, may overheat, or may release heat at the wrong times. Identifying which thermostat is faulty is the first diagnostic step.

What Is Restricted Electrical Work in New Zealand?

This is the most critical point: in New Zealand, replacing a thermostat inside a storage heater is considered restricted electrical work under New Zealand electrical regulations. This means it must be carried out by — or directly supervised by — a registered electrician.

The Electrical Workers Registration Board (EWRB) sets out what work homeowners may and may not do. As a general rule, homeowners can perform certain minor electrical work such as replacing light bulbs or connecting plug-in appliances, but any work that involves opening a fixed appliance and working on internal wiring or components is restricted. Storage heaters are typically hardwired to your home's electrical circuit, which places all internal work firmly in restricted territory.

Attempting this work yourself without the appropriate licence could:

• Void your home insurance
• Create a serious fire or electrocution hazard
• Result in a fine under NZ electrical regulations

What You Can Safely Do as a Homeowner

While the thermostat replacement itself must be done by a professional, there are several things you can safely do beforehand:

• Check the obvious first: Make sure the heater is switched on at the wall and the input/output dials are set correctly. Consult your heater's manual for the recommended settings.
• Test the room temperature: Use a simple thermometer to confirm the room isn't reaching the set temperature, which helps confirm a thermostat fault rather than a user-setting issue.
• Identify the make and model: Locate the rating plate (usually on the back or inside the front panel cover) and note the brand, model number, and thermostat specifications. This helps your electrician source the correct replacement part.
• Switch off the heater safely: Turn off the heater at the wall switch and, if you're comfortable doing so, switch off the dedicated circuit at your switchboard before the electrician arrives. Never open the heater casing while it is energised.
• Check your warranty: If the heater is relatively new, the thermostat replacement may be covered under the manufacturer's warranty or the Consumer Guarantees Act.

Finding the Right Replacement Thermostat

Storage heater thermostats are not universal — they vary by brand, model, and temperature rating. Common brands found in NZ homes include Dimplex and Elnur, among others. Your licensed electrician will be able to source the correct part, but you can assist by:

• Noting the thermostat's temperature range (often printed on the component itself)
• Checking with the manufacturer or a specialist electrical wholesaler
• Searching suppliers such as Placemakers or electrical trade suppliers for compatible parts

Avoid purchasing a generic thermostat without confirming compatibility, as an incorrect temperature rating can create a fire risk.

The Replacement Process (What Your Electrician Will Do)

For your peace of mind, here's a general overview of what a qualified electrician will carry out:

1. Isolate the circuit at the switchboard and verify it is de-energised with a test instrument.
2. Remove the heater casing carefully, noting that storage heater bricks retain heat for many hours — the heater must be fully cooled before work begins.
3. Photograph or note the existing wiring before disconnecting anything.
4. Remove the faulty thermostat and install the correct replacement, ensuring all connections are secure and correctly rated.
5. Reassemble and test the heater through a full charge/discharge cycle.
6. Issue a Certificate of Compliance (CoC) for the electrical work, which is a legal requirement for restricted work in New Zealand.

Healthy Homes and Heating Compliance

If you're a landlord, it's worth noting that working heating is a requirement under the Healthy Homes Standards. A faulty storage heater thermostat that prevents adequate heating could put you in breach of your obligations, so prompt repair is important.

When to Call a Professional

You should contact a licensed electrician if:

• Your storage heater is not charging or releasing heat correctly
• The heater is tripping your circuit breaker
• You can smell burning or see scorch marks near the heater
• The heater is excessively hot to touch on the outer casing
• Any internal component appears damaged

A qualified local electrician can diagnose the fault accurately and carry out the thermostat replacement legally and safely. You can find licensed electricians in your area on tradedirectory.co.nz.

Safety note: Never attempt to open or work inside a storage heater yourself. These appliances operate at mains voltage and store significant thermal energy in their ceramic bricks. Even when switched off, they can remain dangerously hot for many hours.

Sources & Further Reading

• Electrical Workers Registration Board (EWRB) — Restricted Work
• MBIE Building Performance — Electrical Safety
• WorkSafe NZ — Electrical Safety
• Tenancy Services — Healthy Homes Heating Standard
• BRANZ — Home Heating Guidance
• Energywise — Heating Your Home