Ask Our Experts

Here's a conversation I have every year.

Someone calls us in June or July and says their heater stopped working. We ask when they last serviced it. They say never. We ask how old it is. They say five years. We sigh, quietly and professionally, and explain that heaters need maintenance, just like everything else in your van.

The good news is that maintaining an Autoterm or Truma heating system is not complicated. It doesn't require specialist knowledge. It takes a couple of hours and it means your system will start reliably on the coldest night of the year, not fail you at the worst possible time.

Here's what I check, and what your service agent should check, every year before winter.

Pre-Winter Heating Maintenance Checklist

1. Clean the Combustion Chamber

Over time, carbon deposits build up in the combustion chamber of a diesel air heater. In small amounts this is normal. In large amounts it causes inconsistent combustion, hard starting, and eventually heater lockout (the heater shuts itself down as a safety measure).

For Autoterm units, this can be done with a careful disassembly of the combustion head. Your service agent should have the correct tools and the process in the service manual. Don't skip this: it's the single most important maintenance task for a diesel air heater.

2. Check and Clean the Glow Plug

The glow plug is what ignites the fuel in a diesel air heater. If it's fouled with carbon or starting to degrade, starting will become unreliable, especially in cold weather. Glow plugs are consumable items and should be inspected annually. If there's any doubt, replace it: it's a cheap part relative to the cost of a failed heating system.

3. Inspect the Fuel Pump and Fuel Lines

The fuel pump on a diesel air heater delivers a precise metered amount of fuel. If it's running too fast or too slow (which happens as they age), combustion quality degrades. Listen for changes in running sound: a healthy Autoterm has a consistent, rhythmic ticking from the pump. Irregular ticking or silence suggests a problem.

Check all fuel lines for cracks, kinking, or hardening. Older lines can degrade and allow air into the system, which causes starting issues and inconsistent running.

4. Check the Exhaust Outlet

The exhaust outlet must be clear and unobstructed. Make sure it hasn't been covered by storage, modified by a previous owner, or blocked by debris. A restricted exhaust causes incomplete combustion and can cause dangerous carbon monoxide buildup inside the vehicle.

This is a safety check. Do not skip it.

5. Inspect Air Intake and Ducting

Check that the air intake is clear and that all ducting connections are secure and unobstructed. Loose duct connections reduce heating efficiency and can allow warm air to escape into wall cavities rather than the living space.

6. Test the Controller and Thermostat

Fire up the heater before winter. Don't wait until you're parked up on a cold night. Run it through a full heating cycle and check that the controller responds correctly, the thermostat cycles the unit on and off at appropriate temperatures, and there are no error codes.

If you're using the Autoterm Push Button Controller, make sure the display is clear and responsive. If you have an older dial or analogue controller, consider whether an upgrade makes sense.

7. Check the 12V Wiring and Connections

Vibration in a travelling vehicle is hard on electrical connections. Check that all wiring to and from the heater is secure, that connectors haven't corroded or worked loose, and that the fuse is the correct rating and in good condition.

When to Call a Professional

Some maintenance tasks are DIY-friendly. Others aren't. Call a qualified service agent if:

• You have error codes that persist after a basic reset
• The heater starts but doesn't produce adequate heat
• You smell diesel or unusual odours when the heater is running
• The exhaust shows excessive black smoke on startup that doesn't clear
• You've had the unit for more than 3 years and never had it professionally serviced

RV Supplies Can Help

We're the Autoterm and Truma specialist in New Zealand. Whether you need spare parts, technical advice, warranty support, or a referral to a qualified service agent near you, we're the right first call.

Browse our full range of Autoterm and Truma heaters, spare parts, and accessories at rvsupplies.co.nz, or give us a call. We're here to help you stay warm.

Rob Ferguson, Heating Specialist, RV Supplies