No hot water? – blocked Truma Trumatic C3400

A website visitor (Nils Söderberg) was recently reading our article on Truma Trumatic C3402 troubleshooting and posted about an issue he was having with his Trumatic C3400 in a 1996 Hymer B544

He had no flow of water from the system, but the water pump etc. was working OK. After a bit of troubleshooting he found the problem to be a blocked water vessel in the boiler itself – presumably from limescale/sediment build up over the years.

Here is his original comment from when he diagnosed the problem:-

It was the actual truma boiler that was blocket. Somewhere between the frost guard and the boiler.  That was why I could not get any water through the hot water tap. I disconnected the frost guard and the pipe between the frost guard and the boler I could se a sluggish paste in the pipe and since no water came flowing back i suspected that there were something blocking the inlett to the boiler.  I bought a pipe cleaner for kitchen sinks and pulled it back and forth until the water and bits of gray paste started flowing back from the boilers inlett. I connected the pipe back to the valve and drained the boiler from water. Now I have filled the boiler and freshwater tank with a mixture of citric acid and hot water (500gr pr – 50l ). I have flushed it trough the system and are going to leave it in in the boiler overnight. Tomorrow i will use the valve to empty the boiler the bottom so the deposits of scale will hopefully pour out that way and not clog upp something ells. And if more people have the same problem I hope that this description could help them as much as your tear down helped me.

If you are experiencing the same symptoms it is worth following the approach above. Even if you are having no problems it’s a good idea to descale the boiler annually, to help prevent issues like this from occurring.

Many thanks to Nils for the information!


  1. Will citric acid do any harm to the boiler or pipes?

    • Dan

      June 19, 2019 at 5:10 pm

      Hi Tony – are you planning to you citric acid to remove limescale in the system? – I can’t see any reason it would damage either the stainless steel tank in the boiler or the plastic water pipes, but I guess for safety it would be wise to use the weakest solution you think will still be effective. Let us know how you get on if you try it!. Cheers, Dan

  2. Yes thanks Dan I will use a week solution. just wanted to make sure it won’t damage the heater or pipes.

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