Hymer Aktiv – Diesel Heater Glow Plug & Fuel Pump Service

As someone who’s logged over 80,000 miles across North America in three different rigs, I’ve learned a thing or two about keeping my diesel heater in top shape. When I hop into my Hymer Aktiv, I need the assurance that my heater will perform without fail. Many RV owners think of their diesel heaters as “set it and forget it” systems, much like the furnace in their home. But that assumption can lead to a cold winter night, huddled under blankets. The Webasto or Espar heater in your Hymer Aktiv operates on a different level; it’s a precision combustion system that relies on two key components—the glow plug and the fuel pump. Both are prone to wear and tear and can fail regularly. If the glow plug loses its heat or the fuel pump starts to lose pressure, you might not always get a loud warning. Instead, you’ll face unreliable cold starts, stuttering ignitions, or heat that cuts out when you need it most. Fortunately, I’ve handled these repairs myself without needing a dealer or specialized equipment, and I’m here to show you how.

How Your Hymer Aktiv’s Diesel Heater Actually Works

Understanding what you’re troubleshooting is crucial. The Hymer Aktiv is equipped with either a Webasto or Espar diesel heater. Both operate on a simple principle: they pull fuel from the main tank, ignite it inside a sealed combustion chamber, and distribute the resulting heat through ducting into your living space. The two components you need to focus on are the glow plug, which pre-heats the chamber for combustion, and the fuel pump, which delivers atomized diesel to the chamber at the right pressure and volume. You don’t need any special tools or a service bay to replace these parts—both can be fixed in the field in under an hour.

When the Glow Plug Wears Out—And Why You’ll Know It

The glow plug is essential for starting your heater in cold conditions. It heats the combustion chamber enough for the diesel to ignite without needing spark plugs or any external flame. When the ceramic element inside the glow plug starts to wear down, you’ll notice clear signs: your heater will click and grind, the combustion chamber may struggle to ignite, or you’ll find yourself doing multiple restart cycles before it finally catches. Cold mornings become a frustrating guessing game. A warm restart might work fine due to residual heat, but once the rig cools, you’re back to the ignition struggles. That’s the glow plug indicating it’s on its last legs.

What makes this repair doable

• Ceramic elements can endure repeated heating and cooling cycles without cracking, which is crucial for frequent use in varying temperatures.
• Both Webasto and Espar systems use the same direct-fit replacement, so you won’t have to hunt for adapters or cross-reference part numbers.
• Replacing the glow plug is as simple as unscrewing the old one and screwing in the new one, taking roughly 15 minutes once you locate the heater assembly.
• A replacement glow plug costs a fraction of what a dealer would charge just to diagnose the issue, let alone repair it.

Where this approach falls short

• You won’t know for sure that the glow plug was the issue until after you’ve bought a replacement and installed it; accurate diagnosis requires a multimeter and some testing.
• Aftermarket ceramic plugs don’t last indefinitely under heavy winter use—expect around 18 months before you need to replace it again, making this a recurring maintenance task.

I remember ordering a glow plug late one night when it was 22 degrees outside, worried I’d wasted my money if it turned out to be the fuel pump. But when I swapped it in and heard that heater roar back to life, I knew I’d made the right choice. Grab a Webasto / Espar ceramic glow plug for yourself, and you’ll cut out the need for a dealer visit.

Tackling the Fuel Pump—The Unsung Component

The fuel pump serves as the workhorse of your heater. It draws diesel from your tank and pressurizes it into a fine mist that ignites easily in the combustion chamber. When a pump starts to fail, you’ll hear a rising whine or buzz from the heater assembly, which gets more pronounced over days or weeks. The heater might light and then sputter out, or it may ignite but fail to produce full heat, even though the combustion chamber is clearly burning. These are classic signs of pump wear or pressure loss.

Testing the fuel pump requires a bit more effort than checking the glow plug. You’ll want to listen for the pump’s normal humming sound as soon as you power the heater on; that electrical whine should start immediately. Use a multimeter to check if voltage is reaching the pump connector. If the pump is getting power but isn’t making any sound, you’ll need a replacement.

How to replace the fuel pump

Before you begin, place a small drain pan under the heater to catch any residual diesel in the fuel line. The pump is usually bolted directly to the heater housing, secured by one or two fasteners. Disconnect the fuel line (be ready for some spillage) and unplug the electrical connector. Remove the old pump, then install the new one in reverse order, reconnecting both the line and power. The entire job takes about 20-30 minutes. In the Hymer Aktiv, the heater is often located low in the underbody or accessible through a service panel in the floor, making access relatively easy.

Building Heater Reliability Into Your Full-Time Setup

Living and traveling full-time means that your heater isn’t just a convenience; it’s essential. It has to function reliably when the temperature drops. Instead of waiting for failures to happen, I recommend keeping a spare glow plug and an extra fuel pump tucked away in your toolbox. They don’t take up much space, are inexpensive, and can be lifesavers when you’re parked in a remote spot in January without cell service or a nearby dealership. Having these backups allows you to turn a potential breakdown into a quick 20-minute roadside repair.

Also, pay attention to your fuel supply. Diesel can pick up water and sediment if it sits in tanks for extended periods, which can hinder the fuel pump and accelerate wear on the glow plug. If your heater starts to behave erratically or won’t fire up after sitting idle, reach for a diesel fuel system additive specifically designed for RVs. This preventive maintenance is inexpensive and can save you from a breakdown in the field.

The Bottom Line

Both the glow plug and fuel pump are within reach for anyone willing to tackle DIY repairs. They cost significantly less than a dealer visit and can be replaced in under an hour on your own schedule. The glow plug is straightforward—if you’ve ever changed a car’s spark plug, you already have the basic skill. The fuel pump is a bit more involved but still manageable. By addressing these two common failure points in your Webasto or Espar system yourself, you reclaim control over your heating reliability. You can skip the dealer queue, avoid mystery diagnoses, and eliminate unnecessary waiting.

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Part-Level Diagnostics

This guide covers the tear-down on this coach. If you have already narrowed the fault to one component, these go deeper on diagnosing and replacing the individual part:

• Start here: the inline fuel filter is the cheapest fix for a no-start
• Fuel pump not clicking? Test the dosing pump before replacing it
• Glow plug symptoms: white smoke, failed ignition, and how to test it
• Blower motor: rattles, slow spin-up and overheat shutdowns