Truma Combi Boiler: Annual Service & Fault Diagnosis
Step-by-step guide to servicing your Truma Combi 4 or 6 boiler, including burner cleaning, heat exchanger inspection, and common fault codes explained.
What This Is
The Truma Combi is the most popular combined space heater and water heater in UK motorhomes. Annual owner-level maintenance keeps it running reliably and avoids costly call-outs.
Tools & Parts Required
- Truma service kit
- Soft brush
- Vacuum cleaner
- Multimeter
- Torx screwdriver set
- CO detector
Step-by-Step Instructions
- 1
Turn off the gas at the LPG bottle and switch off the Truma Combi at the control panel. Allow the unit to cool completely — at least 30 minutes after last use. Disconnect the 12V supply at the fuse box.
- 2
Remove the four Torx screws securing the front panel. Carefully unclip the panel and set aside. You will see the burner assembly, heat exchanger, and circulation pump.
- 3
Using a soft brush, gently clean the burner head of any dust, cobwebs, or debris. Insects — particularly wasps and spiders — frequently nest in the air intake during summer storage. Use a vacuum cleaner with a narrow nozzle to remove all debris.
- 4
Visually inspect the heat exchanger fins for corrosion, scale, or blockage. Gently brush the fins clean. If significant scale is present, the system may need descaling with a proprietary motorhome system descaler.
- 5
With power restored (gas still off), switch the boiler to heating mode and listen for the circulation pump running. A grinding or absent sound indicates a seized pump — a common fault after winter lay-up. Pumps can often be freed by removing the pump head and manually turning the impeller.
- 6
Check the pressure gauge — it should read 1.0–1.5 bar when cold. If below 0.5 bar, top up via the filling loop. Repeatedly dropping pressure indicates a failed expansion vessel diaphragm.
- 7
Restore the gas supply and power. Set the Truma to heating mode and observe the ignition sequence. You should hear three ignition clicks followed by a steady flame. The status light should show green.
- 8
Common fault codes — F10: Overheating (check pump). F13: Flue sensor fault. F20: Flame failure (clean burner, check gas). F30: Fan fault. E1: Ignition lockout (reset and retry; if persistent, call Gas Safe engineer).
- 9
Refit the front panel. Run the boiler through a full heating cycle, checking all radiators and hot water outlets. Check for any gas smell — if detected, shut off immediately and call 0800 111 999.
Common Mistakes to Avoid
- Ignoring cobwebs and insect nests in the burner — the most common cause of ignition failure
- Running the boiler without checking water pressure first
- Forgetting to bleed air from the heating circuit after refilling
Safety Warnings
- Always isolate the gas supply at the bottle before starting.
- Allow the unit to cool completely before opening — at least 30 minutes.
- Any gas-side work must be carried out by a Gas Safe registered engineer.
When to Call a Professional
Any fault codes that persist after basic cleaning, gas valve replacement, heat exchanger leaks, or if you smell gas at any point.
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