Paullus1959Not a very technical answer I'm afraid but, I understand you have to push the knob on the top of the heater in to activate the piezo ignition. Is it possible the knob isn't returning fully maybe due accumulated dust causing it to stick down a bit.
If it was mine, the first thing I'd try would be to pull the knob off and give the stem a squirt of WD40 or similar and then replace the knob and work it up and down a few times to see if it frees up.
Worth a try.
Welcome to the forum.
I presume your heater is a Truma S 3000 series model, These use an automatic electronic ignitor Technically it's a re-ignitor becasue it has a flame sensing circuit built into it which when it detects a flame it stops the ignitor from sparking. It does this by looking for a conductive path to be completed between the spark probe and the grounded burner bar by the flame.
The ignitor is controlled by a small micro switch inside the top of the gas valve . so when the valve is turned on the power to the ignitor is also turned on. But as the ignitor runs when the valve id on and stops when its off suggests this is working correctly.
The fact the ignitor continues continues to run when the flame is present suggests four possible faults.
1. The high tension wire or electrode is damaged loosing the conductive path for the flame detection system (the High Tension spark will jump small breaks which will defeat lower voltages.)
2. The flame shape or position could be wrong - A blocked burner could cause a small or miss-shaped flame preventing the flame from completing the circuit. This is a job for a qualified caravan gas fitter
3. There are a pair of wires that connect the ignitor to the micro-switch. One of those wires ( and I cant remember whether its the brown or black) must be clamped firmly to the grounded base plate of the heater
4. The ignitor could be faulty. This can be easily replaced if necessary, but it tends to be quite expensive.
Good point. And it's why on the older SL 3002 heaters (I don't know it the more modern versions have it) there should be a bent metal plate behind the ignitor block to act as a heat shield.If the flame stays lit when the gas control knob is released and the ignition box keeps ticking then it’s normally the ignition box, often heat damaged.
The flame detection I have been referring to is the electronic signal the ignitor block uses to stop the spark. Its totally independent of the Flame Failure Device (FFD) which uses a thermocouple in the flame and solenoid in the gas valve to shut the gas flow off if the flame is lost for more than a few seconds.If the flame retraction wasn’t working it wouldn’t hold flame 🤔