Everyday care rules for HLN diesel heaters, answered from the official manuals. Five minutes of reading here prevents 90% of winter service calls.

Which fuel? Match the diesel grade to the temperature

Use diesel appropriate for the ambient temperature: 0# diesel above 5°C · -10# above -5°C · -20# above -15°C · -35# above -30°C · -50# above -40°C. Summer diesel gels in the cold and is the classic cause of winter no-starts. Never blend used engine oil into the fuel.

Diesel models burn ONLY diesel — gasoline models ONLY gasoline

On diesel models (Aerolyn air heaters, Aquano diesel hydronic), any fuel other than diesel is strictly prohibited. HLN also makes a dedicated gasoline hydronic model — that one burns only gasoline. Never put the wrong fuel in either type: it damages the combustion chamber and creates a fire risk. If the wrong fuel was added, do not ignite the heater — contact us first.

The 3-minute cooldown rule (most-broken rule in the manual)

Turn the heater off at least 3 minutes before cutting the vehicle's main power. After shutdown the fan keeps running for ~3 minutes to blow-cool the body — that is normal, let it finish. Cutting power mid-cooldown traps heat and damages the heater.

Watch the correct shutdown — what the OFF purge looks like on the ComfortStart controller:

Turn the heater off before refueling

Always switch the heater off before refueling the vehicle.

Run it 15–20 minutes every month — even in summer

During seasons when the heater is not in use, run it 15–20 minutes monthly. This keeps the fuel system primed, prevents pump seizure, and keeps seals healthy.

Routine checks

At every vehicle service: look for fuel seepage under the heater (leaks are a fire risk), confirm intake/exhaust are unobstructed, keep battery terminals clean, and before first use each season verify air paths are clear and combustion is smooth.

Fuel quantity spec (the 5-minute test)

Over a timed 300-second full-power test the heater should deliver 50 ml ±10% (45–55 ml) of fuel. Above spec: replace the fuel metering pump. Below spec: check the pump filter, line routing and hose clamps. Fuel quantity is not affected by voltage variances.

Don't throw an ECU at the problem

99% of repaired heaters did not need a new ECU. Always work through the diagnostic sequence (error-code guide, no-start guide) before replacing expensive components.

E13 with white smoke — the four usual suspects

(1) Blocked intake/exhaust: remove both tubes and test-start with open ports — if it starts, clear the blockage. (2) Flooded chamber after repeated failed starts: unplug the fuel pump wire, run two cycles to burn off excess fuel, reconnect. (3) Continuous heavy white smoke: carbon build-up — the chamber needs opening and cleaning. (4) Small puffs only at low temperature: suspect fuel waxing — switch to winter diesel. If you smell raw fuel or smoke turns black, stop and contact us.

No modifications, original parts only

Modifying the heater or repairing with non-original parts is prohibited and voids the warranty. Installation and repair should be done by trained personnel with the proper documentation and tools.

Questions the manual doesn't answer?

Email kevin@hlnind.com — real HLN engineers answer, usually within a day.

About HLN — For 50+ years HLN has built diesel air and hydronic heaters as original equipment for major truck, bus and RV manufacturers (YuTong, SANY, XCMG and two Fortune-500 truck makers), with CE / ECE R122 / R10 certification. Shop heaters and parts: Aerolyn 2kW, Aerolyn 4kW, Aquano 5K hydronic, fuel pump, glow pin.