When your rig is your permanent address, calling a dealer and waiting three weeks for a service appointment isn’t an option. You fix it yourself, you fix it now, and you fix it right — because your home doesn’t get to sit broken on a lift. The Webasto or Espar diesel heater in the Hymer Aktiv is one of those systems you don’t fully appreciate until it quits on a 28-degree night — and when it does, a failed glow plug or a stuttering fuel pump is almost always the culprit. These parts are wear items, they fail predictably, and with the right steps they’re well within reach of anyone comfortable turning a wrench in a tight space. This guide walks you through the full diagnostic and replacement process the way a full-timer actually does it — no dealership, no mystery, no excuses.
Understanding Your Hymer Aktiv’s Diesel Heater System
Before you start pulling parts, it helps to understand what you’re working with. The Hymer Aktiv uses either a Webasto or Espar diesel heater—both are solid-state systems that draw fuel from your main tank, ignite it in a combustion chamber, and circulate warm air through ducting to your living space. The glow plug and fuel pump are the two components most likely to fail, and both are field-replaceable without specialized equipment or a lift. The glow plug heats the combustion chamber to trigger ignition; the fuel pump atomizes diesel into a fine mist for efficient burning. When either one falters, your heater becomes unreliable at best and completely dead at worst.
The Glow Plug That Finally Stopped the Cold-Start Guessing Game
A failed glow plug is the silent killer of winter mornings in a Hymer Aktiv—your heater clicks, the combustion chamber struggles, and you’re left wondering if you’re looking at a $400 dealer visit or a $30 fix. The ceramic glow plug is almost always the culprit, and replacing it yourself means heat on your terms, not the service department’s schedule.
The classic sign of a failing glow plug is a heater that ignites intermittently or requires multiple restart attempts before catching. You might also notice that cold starts are unreliable but warm restarts work fine—this tells you the combustion chamber isn’t being pre-heated adequately. On frigid mornings, the glow plug has to do all the heavy lifting, and a worn one simply can’t generate enough heat.
What works
- Ceramic construction handles repeated thermal cycling without cracking—critical when you’re heating on demand in variable climates.
- Direct fit for both Webasto and Espar systems means no guessing about compatibility or adapter hunting mid-winter.
- Replacement takes 15 minutes once you’ve located the heater element; the glow plug unscrews like a spark plug and needs no special tools.
- Cost savings are immediate and substantial compared to a dealer service call, which often includes diagnostic fees and labor.
What doesn’t
- You won’t know if the glow plug was actually the problem until you’ve already bought one; testing requires a multimeter and some electrical troubleshooting confidence.
- Aftermarket ceramic plugs can fail within 18 months of heavy use—this isn’t a permanent solution, just a reliable Band-Aid.
I ordered one at midnight on a 22-degree night convinced I’d wasted money if the fuel pump was the real culprit, but swapping it in and hearing that heater fire up again made it impossible to regret keeping my rig’s warmth in my own hands. Grab a Webasto / Espar ceramic glow plug and you’ll have one less reason to sit in a dealer’s waiting room.
Diagnosing and Replacing the Fuel Pump
The fuel pump is the heater’s unsung workhorse. It pressurizes diesel from your tank and delivers it to the combustion chamber in a steady, atomized stream. When a fuel pump starts failing, you’ll typically hear a faint whine or buzzing from the heater assembly that gradually becomes louder. The heater might start, sputter, and cut out, or it might struggle to reach full heat output even though the combustion chamber ignites normally.
Testing a fuel pump is more involved than testing a glow plug. You’ll need to listen carefully for the pump’s characteristic hum when you first power on the heater, and you can use a multimeter to check for voltage at the pump connector. A pump that’s receiving power but making no sound is almost certainly dead.
Fuel Pump Replacement Steps
Replacing the fuel pump requires draining residual fuel from the heater’s fuel line—have a small container ready. The pump itself is usually mounted directly on the heater housing and held with one or two screws. Disconnect the fuel line and electrical connector, remove the old pump, and install the new one in reverse order. This job takes 20–30 minutes and is straightforward once you’ve located the heater unit. On a Hymer Aktiv, that’s typically mounted low and forward in the underbody, accessible from underneath or from a service panel inside the living space.
A Full-Timer’s Approach to Heater Reliability
When you live in your rig year-round, heater reliability isn’t luxury—it’s survival infrastructure. Rather than waiting for parts to fail, savvy full-timers carry a spare glow plug and fuel pump filter as part of their rolling toolkit. Both are inexpensive insurance, and both fit in a small bag that takes up almost no storage space. If you’re boondocking in remote areas during winter, having backups means the difference between comfort and a cold night spent weighing your options.
Beyond parts, keep your fuel clean. Diesel that’s been sitting in tanks for months can develop water contamination and sediment, which clogs the fuel pump and accelerates glow plug wear. If your heater runs rough or fails to start after sitting idle for a few weeks, add a quality diesel fuel additive designed for RVs. It’s cheap prevention that often saves you from a roadside breakdown.
The Verdict
Both the glow plug and fuel pump on a Hymer Aktiv are field-replaceable, affordable, and well worth tackling yourself rather than booking a dealer appointment. The glow plug swap is genuinely trivial—if you can unscrew a spark plug, you can handle this. The fuel pump takes slightly longer but is still well within reach of any DIYer. Between the two, you’ve eliminated the two most common failure points in a Webasto or Espar system, and you’ve done it on your own schedule, in your own driveway, without begging a service department for an appointment that won’t happen for weeks.
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