Whale Expanse Water Heater: Operation, Servicing & Fault Diagnosis

What This Is

The Whale Expanse is a compact, gas-fired instantaneous water heater widely fitted in UK-built motorhomes, caravans, and campervans from the late 1990s onwards. Unlike a storage boiler such as the Truma Combi, the Expanse heats water on demand as it flows through the unit — there is no hot water tank. It is typically rated at 10 or 14 litres per minute and runs on LPG (butane or propane). The unit is usually mounted in a habitation locker or under a bed, with a flue venting through the vehicle wall. Understanding how your Expanse works is the key to diagnosing faults quickly. The unit uses a water flow sensor to detect when a tap is opened. This triggers the gas valve and an electronic ignition sequence. If the ignition is successful, the burner fires and heats the water as it passes through the heat exchanger. When the tap is closed, flow stops and the burner shuts off automatically. The Expanse is a reliable unit when properly maintained, but it is sensitive to low water pressure, dirty filters, and scale build-up in hard water areas. Most faults can be resolved by the owner without specialist tools.

Tools & Parts Required

Step-by-Step Instructions

1. 1

   Turn off the gas supply at the regulator or gas locker valve before starting any work. Open a hot tap to release any residual pressure in the system. Turn off the water pump.

2. 2

   Locate the Whale Expanse unit — typically in a locker, under a bed, or behind a panel. Remove the front cover by undoing the two screws at the base. The cover lifts away to reveal the burner assembly, heat exchanger, and control board.

3. 3

   Inspect the inlet water filter. This is a small mesh filter fitted to the cold water inlet connection (usually the lower pipe). Unscrew the inlet connector carefully — have a towel ready for drips. Remove the filter mesh, rinse under clean water, and use a fine brush to remove any debris. Refit and tighten firmly.

4. 4

   Check the flow sensor. The flow sensor is a small turbine on the cold water inlet. Gently spin the turbine with a finger — it should rotate freely. If it is stiff or jammed, it will prevent the unit from igniting. Flush with clean water to clear any debris.

5. 5

   Inspect the burner. The burner is the metal assembly at the base of the heat exchanger. Look for carbon deposits, spider webs, or insect nests — these are a very common cause of ignition failure, especially after winter storage. Use a fine wire brush to gently clean the burner ports. Do not use compressed air as this can damage the igniter electrode.

6. 6

   Check the igniter electrode. The electrode is a small ceramic-tipped probe positioned next to the burner. It should be clean and free of carbon. The gap between the electrode tip and the burner should be approximately 3–4mm. If the tip is cracked or heavily carbonised, the electrode needs replacing.

7. 7

   Inspect the thermocouple or flame sensor. This is the probe that detects whether the burner has lit. If it is coated in carbon or soot, the unit may shut down immediately after ignition. Clean gently with fine wire wool or emery cloth.

8. 8

   Check the heat exchanger for scale. In hard water areas, calcium deposits build up inside the heat exchanger coils, reducing flow and efficiency. If you notice reduced hot water flow or lukewarm output, descaling is required. Disconnect the inlet and outlet water pipes, connect a descaling solution (diluted citric acid works well) using a small pump or gravity feed, and allow to soak for 30–60 minutes. Flush thoroughly with clean water before reconnecting.

9. 9

   Inspect all gas connections at the unit for tightness. Do not overtighten — hand tight plus a quarter turn with a spanner is sufficient for compression fittings. Apply gas leak detection spray or soapy water to all joints after reconnecting the gas supply.

10. 10

    Refit the front cover. Restore the gas supply and water pump. Open a hot tap fully and allow the system to purge air. The Expanse should ignite within 2–3 seconds of water flowing. You will hear a click from the igniter followed by the burner lighting. Hot water should flow within 5–10 seconds.

11. 11

    Check the flue outlet on the outside of the vehicle. The flue should be clear of obstructions, bird nests, and debris. A blocked flue is a serious safety hazard — it can cause combustion gases to enter the vehicle. Clean with a bottle brush if necessary.

Common Mistakes to Avoid

Safety Warnings

When to Call a Professional