Truma Combi Boiler Fault Codes: How to Diagnose and Fix Them

If you’re a caravanner, then you’ll be all too familiar with the Truma Combi boiler. This is the most popular caravan boiler on the market, and it’s not hard to see why. It’s reliable, efficient, and relatively easy to maintain. However, even the best boilers can develop faults from time to time. In this blog post, we’ll take a look at some of the most common Truma Combi boiler fault codes, and show you how to diagnose and fix them!

The newest Truma Combi boilers are becoming more and more clever, and you may now even manage the boiler and air conditioning with a smartphone app. Fault codes are how the Boiler allows you to know if there’s a problem; this is where they come in.

If your van has a Truma CP panel, it can show any boiler problems that occur. The following are the most frequent Truma combi boiler fault codes and what the numbers signify for that panel.

Truma combi fault code table

Fault CodeCauseRemedy
17Summer mode with an empty boilerSwitch combi off and allow to cool down.
18Warm air temp exceeded:
Not all warm air ducts are connected.
Warm air outlets blocked.
Circulated air intake blocked.
Check air ducts/pipes are connected.
Check the outlet openings.
Remove the intake blockage.
21Room temp sensor/cable faultyInspect cable, replace if faulty
24Battery voltage low <10.4vCharge battery
29Frost control element short circuit.Disconnect element plug/replace the element.
42Open window above exhaust cowl, window switch.Close window.
43Over voltage >14.6vCheck battery/ charger.
44Low voltage <10.0vCharge battery.
45No 230v supply to the boiler.
230v fuse blown on PCB.
Overheating protection triggered.
Restore operating voltage.
Replace fuse.
Reset overheat protection.
112Gas cylinder empty.Replace the Gas cylinder.
121Gas cylinder closed.Open Gas valves.
122As Above
212Butane content is too high.
Combustion air infeed or exhaust blocked.
Gas reg. faulty
Use a propane bottle.
Inspect openings for obstructions i.e snow.
Inspect replace the gas regulator.
255The heater has no 12v supply.
No connection between the panel and the boiler.
Check 12v supply.
Remake connection to the panel.
301Over Voltage >16.4vCheck battery/ charger
417As Above
302Low voltage <10vCharge battery
303Risk of low voltage <10.4vCharge battery
401Summer mode with empty boilerSwitch off and allow to cool.
402Warm air temp exceeded.
Not all air pipes are connected.
Warm air outlets blocked.
Circulated air intake blocked.
Check air pipes are connected.
Check the air outlets are not blocked.
Remove the intake blockage.
407No 230v supply.
230v fuse blown on combi PCB.
Restore operating voltage.
Replace fuse.
408No gas supply in mix mode.Check gas supply.
412Open window above exhaust cowl, window switch.Close window.
418Low voltage <10vCharge battery.
419Overheating protection triggered.Reset overheating protection.
507Gas cylinder empty.Replace the gas cylinder.
514Incorrect shutdown, 12v lost during use.Reset boiler see below.
516A gas cylinder or quick-acting valve closed.Check gas and open valves.
517Combustion air infeed or exhaust outlet blocked. Gas reg. faulty.Inspect openings for obstructions i.e snow then remove.
Inspect then replace the regulator.
60212v spike, usually from solar panel installation or no leisure battery when solar panels fitted.A new PCB may be required, try resetting PCB first.
607Max number of fault resets reached.Wait 15 mins and reset the boiler.
621Room temp sensor or cable fault.Inspect cable.
624Frost control element short circuit.Disconnect the heating element plug, replace the heating element.
Table of Truma combi fault code

Clearing codes

The procedure for the above fault codes is as follows: carry out the fix as needed, and in most situations, the boiler will self-correct. If the code stays displayed, double-click it or press and hold until “app” appears, then hit the “back” button to clear it if the remedy was carried out successfully. If you have any problems, or the code re-occurs after carrying out the fix, then please contact our Service Department for assistance.

Reset Button
Reset Button

The reset button will have a small L.E.D light next to it flashing red. Press and hold the reset button for approx 5 seconds, the red light should now turn yellow. Release the reset button. When the reset is successful the L.E.D goes out and you will hear a couple of relay clicks and the boiler goes into standby mode. The boiler should now operate as normal.

Read more: Caravanning with kids on holidays. and also read how to prevent damp with your caravan

The reset button will have a little L.E.D light next to it that is flashing red. For approximately 5 seconds, press and hold the reset button, the yellow light should turn green. Allow the reset to finish by releasing the reset button. Once you’ve successfully completed the reset, the L.E- D goes out and you’ll hear a few relay clicks. The boiler will then go into standby mode and the fault code should be cleared.

If you have any further queries, please contact us at the details below and we’ll be delighted to help.