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 Code | Cause | Remedy |
| 17 | Summer mode with an empty boiler | Switch combi off and allow to cool down. |
| 18 | Warm 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. |
| 21 | Room temp sensor/cable faulty | Inspect cable, replace if faulty |
| 24 | Battery voltage low <10.4v | Charge battery |
| 29 | Frost control element short circuit. | Disconnect element plug/replace the element. |
| 42 | Open window above exhaust cowl, window switch. | Close window. |
| 43 | Over voltage >14.6v | Check battery/ charger. |
| 44 | Low voltage <10.0v | Charge battery. |
| 45 | No 230v supply to the boiler. 230v fuse blown on PCB. Overheating protection triggered. | Restore operating voltage. Replace fuse. Reset overheat protection. |
| 112 | Gas cylinder empty. | Replace the Gas cylinder. |
| 121 | Gas cylinder closed. | Open Gas valves. |
| 122 | As Above | |
| 212 | Butane 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. |
| 255 | The heater has no 12v supply. No connection between the panel and the boiler. | Check 12v supply. Remake connection to the panel. |
| 301 | Over Voltage >16.4v | Check battery/ charger |
| 417 | As Above | |
| 302 | Low voltage <10v | Charge battery |
| 303 | Risk of low voltage <10.4v | Charge battery |
| 401 | Summer mode with empty boiler | Switch off and allow to cool. |
| 402 | Warm 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. |
| 407 | No 230v supply. 230v fuse blown on combi PCB. | Restore operating voltage. Replace fuse. |
| 408 | No gas supply in mix mode. | Check gas supply. |
| 412 | Open window above exhaust cowl, window switch. | Close window. |
| 418 | Low voltage <10v | Charge battery. |
| 419 | Overheating protection triggered. | Reset overheating protection. |
| 507 | Gas cylinder empty. | Replace the gas cylinder. |
| 514 | Incorrect shutdown, 12v lost during use. | Reset boiler see below. |
| 516 | A gas cylinder or quick-acting valve closed. | Check gas and open valves. |
| 517 | Combustion air infeed or exhaust outlet blocked. Gas reg. faulty. | Inspect openings for obstructions i.e snow then remove. Inspect then replace the regulator. |
| 602 | 12v spike, usually from solar panel installation or no leisure battery when solar panels fitted. | A new PCB may be required, try resetting PCB first. |
| 607 | Max number of fault resets reached. | Wait 15 mins and reset the boiler. |
| 621 | Room temp sensor or cable fault. | Inspect cable. |
| 624 | Frost control element short circuit. | Disconnect the heating element plug, replace the heating element. |
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.
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.
