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Boiler Overflow on Truma C Boiler


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Hi, new here so any advice appreciated!


We have a problem with our Hymer Camp Swing 544 (1998 reg) that I hope you can help with. When the water pump is on the and the taps are turned on in toilet sink or kitchen sink, the water comes out of a pipe situated under the van, underneath where the boiler (truma C) is housed.


There are 2 pipes there, one is for the anti-frost feature (that you open with the pull pin in the boiler storage area). However the water is not coming from that pipe, it is coming from one next to it. From research, this is the overflow pipe, and when the taps are on a 'gushing' sound happens and it looks like that instead of water going into the red hot water pipe, that is pushed up the clear pipe and out the outlet under the van (underneath boiler). I have done this after filling the boiler by opening the cold water tap, and when I have cleared the water from the boiler using the frost control pull pin, water comes out as it should, so there is water going into the boiler.


I've disconnected the hot water pipe in the bathroom, and there is no water in the pipe.


Am I correct in thinking that the hot water pipe from the boiler to the sink is blocked and all the water is being forced out the outlet pipe? We haven't used the taps for over 2 years, so would it be possible that is an air block, and if not what else could it be?


And if either an airblock, or something else, would anyone have any tips on how to unblock/clean.

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It sounds like you may be experiencing a similar problem to that being described in the other current thread, here:




It is essentially the same system, though the boiler is badged differently.


The "overflow" you refer to is probably the outlet from the "breather" valve in the hot water outlet. This is designed to allow air to escape whilst the boiler is being filled, etc, but should close when it is filled.


It is known to "stick", then any water under pressure will take the route of least resistance - through the vent/overflow pipe. If it is that, you could attempt to clean it, but at around £15 or so for a Truma replacement, reasonably easily obtained, it's probably best to change it.


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This (sometimes infuriating!) 2009 forum discussion related to a similar problem (coincidentally also on a Hymer)




and Mick H’s posting of 12 April 2009 11:37 AM shows the clear plastic tube through which water was flowing from the heater’s vent-valve (‘breather’).


As Robinhood has advised (and also because your Hymer is 1998-vintage) if the vent-valve is failing to close when the heater is being filled, you’d be best to replace the vent-valve with a new one.


Make sure you get the appropriate vent-valve according to whether your Hymer has push-fit (1st image below) or ‘jubilee clip’ (2nd image below) water connectors.


(Historically, the vent-valve’s tube went vertically upwards: nowadays the valve is ‘elbow shaped’ and the tube goes horizontally.)



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