Truma UltraRapid Hot Water System problem

.
Paul,

That sounds very much like insufficient 12v at the heater. The fact that it is more reliable soon after driving but then fails after being parked signals this. Your battery is being charged whilst driving so its voltage is at its best for a while after stopping, then drops away. This may also be a sign of a poor battery and the current-carrying capacity of the wiring to the heater can play a part. The fact that it works fine on ac also supports this.

I know that you observe "over 12v" at the heater but I still question if this is correct. How accurate is your voltmeter? Can you compare it to another one?
Re the "over 12v" you have observed...... is this reading obtained whilst the heater is actually "ticking", that is, with the heater load on the battery? With a freshly charged battery you should be seeing at least 12.5v

It is also possible that the heater is needing more voltage than "over 12v" and when using mains power the ac-dc component of the heater is providing this higher voltage so it then works OK, but fails on the possibly lower voltage when operating from the battery. Measuring voltage on the downstream side of the 230v to 12v component would check this.

Paul
I haven't seen inside a Truma unit but it sounds like the flame detector isn't always telling the circuitry there is a flame and so it won't continue or run the main burner either. The gas pressure would be the same as the reg pressure and probably is checked while running. Is it possible to view the flame detector for obstruction or dust etc. That may be not be detecting flame and so switches off the gas. Being intermittent. Are you able to see if it does in fact light up then stops and retries?

Low gas pressure is listed as a cause of red lamp failures after approximately 30 seconds, but marginal gas pressure can cause intermittent red lamp failures at any time. The manual recommends 2.75kPa for Propane, which would have to be checked by a gasfitter.

Why not try a new regulator if you can, sound like gas pressure to me
bob

Technically your Truma is definitely not out of warranty under Australian consumer law. Your Truma infact has Statutory Warranty which Consumer Affairs in your state I would expect the unit to be good for service for a minimum of three years and would expect five years. Consequently your unit is definitely not out of warranty by Dometic or your caravan manufacturer. Tell your caravan dealer to fix the Truma unit to your satisfaction otherwise you will proceed to Consumer Affairs who will back you up 100%.
There may also be an issue with a kink or bad connection to undersize piping on the hot water system. Being a Truma a faulty oxygen sensor wouldn't be out of the question either.

These units have had there problems, you will find Domectic have passed the baton onto another company. Dust in the area around the air inlet have caused some of these problems, Give a good cleanout with a blower vac. Try turning it on after dark and watch what is happening through the outside vent.
Other things to look out for is loose connectors on the PC board , loose PC board in its female connectors
Broken capacitors on the PC boards and fine leaks caused by expansion of the boiler welds when water is hot .
All the above caused by corrigations and dust -
" They are not made for constant or off road conditions" - quote from the service agent !

You do not say if the gas ingites then goes out, or if the gas fails to ignite at all? Mine is not a Truma but will ignite the go out, it will then try to reignite and I can hear the sparker clicking. Usually this is caused by dust or dirt even wasp nests in the flame tube or adverse wind. A good blow with compressed air mostly gets it working.