The Truma 5002 and it's similar siblings are fitted to most Classic Hymers. After many years of good service, eventually they can refuse to light. The fix can be quite easy if you know where to look.
This is how it should work. You push and turn the knob 23. This operates the gas supply and also an electrical switch in the base - 29. This closes the circit in the two switching wires 28, that go to the ignition unit 19. This generates a spark, which goes down wire 42 to the igniter electrode 41. When the fire lights, a flame sensor allows the gas to keep flowing and cuts out the igniter switch so that the ticking stops.
The first thing you need to do is remove the cover - lift and pull forward. Then you need to look for a small plastic box at the lower left - this is the igniter unit - item 19 in the drawing.
Operate the control knob as if to light the fire, and listen closely for the familiar tic tic sound from the box. If you hear nothing, then you need to look at the igniter. There are 2 types - the commonest has a single AA battery inside. Less commonly the box is powered directly from the van 12v system. The commonest fault is of course a flat battery. Replace the battery and the box should start ticking again and the fire should light.
The fun starts if you replace the battery and the box doesn't tic. There are usually three possible causes for this. The first is that the box is broken and needs replacing. The second is that the spark wire that leads from the back of the box and into the depths of the fire to the burner has worn out somewhere and the spark is escaping to ground before it reaches the burner. The third is that the other two small wires leading to the box - the switching wires - have come loose or are otherwise broken. They come from the bottom of the control knob shaft. When you turn the knob, the circuit is completed and the box should tic.
On igniters that are powered by the van 12v circuit there will be extra wires for this. In this case you must check that the igniter is receiving 12v - the only way to do this properly is with a test meter.
On a battery powered igniter (with a new battery!) you need to check is the unit generating a spark. Unplug the spark wire from the back of the unit and operate the control - you should hear a tic tic. If not, you need to test the switching circuit. Note where the two wires come from the control knob items 27/28 on the diagram, remove the wires from the back of the igniter unit, exposing the pins, and then short out those two pins with the tip of a screwdriver - at 28. If you get a tic, then you have proved that there is a fault in the switching circuit. Look for a break in the wires. Check the wires where they join the bottom of the control knob shaft - I have never known one to fail here, but you never know.
You need to definitely prove if the ignition unit is generating a spark tic. If it is not, then you need a new ignition unit.
If after changing the battery and operating the switch you are definitely generating a tic, but the fire is not lighting, then the most likely problem is the spark wire that goes from the igniter to the burner - item 42 to 41. After many years this wire gets old and the insulation can break down, and the spark can escape to chassis in many places. Sometimes if you listen very closely you can hear a very weak tic tic but the fire will not light. This is a good clue that the spark lead is broken or worn - it is shorting out before it reaches the burner. But it is important that you prove which is faulty - the ignition unit, or the spark lead - because changing the ignition unit is easy, but will be no good if the spark lead is faulty. Changing the spark lead is more complicated, so you must be sure that is the problem.
Changing the spark lead is a job for an engineer or a very keen DIYer. It's not rocket science, but you are dealing with gas and fumes, so you must either be competent, or don't bother.
NOTE - the drawing below is for a double burner fire - the single burner models are the same in principle.
The sequence of events is as follows. Remove the chimney pipe - item 1. Undo the lock ring and pull the pipe away. There is a silicone O ring that seals the joint. This a safety critical component and should be replaced - order one at the same time you order a new spark lead - items 8 and 42. Disconnect the gas feed pipe - if you don't know how to do this safely and competently, then you shouldn't even be attempting the job. Then remove the screws that attach the fire base plate 12 to the wooden plinth. The whole fire should now lift up and out. You are looking for the burner box 44 that protrudes down into the open below the van - either a single or a double depending on your fire. Clip 46 releases the cover and gets you inside. Then it should be obvious where the spark electrode 41 is, and trace its feed wire 42. You should see where the problem is - quite often I have seen the wire just crumble to dust. You can make your own DIY wire if you are competent, or order one. Make sure you have a good spark before re-assembly.
Once you get the thing in bits, it's all reasonably logical. The awkward and dangerous bits are the chimney joint and the gas connection. The silicon O ring is essential to be properly placed - it stops fumes from escaping the joint and into the van. And as already stated, the gas connection is an obvious point of danger if not done properly. Do not undo and redo gas pipes unless you have learnt the proper protocols.
This is how it should work. You push and turn the knob 23. This operates the gas supply and also an electrical switch in the base - 29. This closes the circit in the two switching wires 28, that go to the ignition unit 19. This generates a spark, which goes down wire 42 to the igniter electrode 41. When the fire lights, a flame sensor allows the gas to keep flowing and cuts out the igniter switch so that the ticking stops.
The first thing you need to do is remove the cover - lift and pull forward. Then you need to look for a small plastic box at the lower left - this is the igniter unit - item 19 in the drawing.
Operate the control knob as if to light the fire, and listen closely for the familiar tic tic sound from the box. If you hear nothing, then you need to look at the igniter. There are 2 types - the commonest has a single AA battery inside. Less commonly the box is powered directly from the van 12v system. The commonest fault is of course a flat battery. Replace the battery and the box should start ticking again and the fire should light.
The fun starts if you replace the battery and the box doesn't tic. There are usually three possible causes for this. The first is that the box is broken and needs replacing. The second is that the spark wire that leads from the back of the box and into the depths of the fire to the burner has worn out somewhere and the spark is escaping to ground before it reaches the burner. The third is that the other two small wires leading to the box - the switching wires - have come loose or are otherwise broken. They come from the bottom of the control knob shaft. When you turn the knob, the circuit is completed and the box should tic.
On igniters that are powered by the van 12v circuit there will be extra wires for this. In this case you must check that the igniter is receiving 12v - the only way to do this properly is with a test meter.
On a battery powered igniter (with a new battery!) you need to check is the unit generating a spark. Unplug the spark wire from the back of the unit and operate the control - you should hear a tic tic. If not, you need to test the switching circuit. Note where the two wires come from the control knob items 27/28 on the diagram, remove the wires from the back of the igniter unit, exposing the pins, and then short out those two pins with the tip of a screwdriver - at 28. If you get a tic, then you have proved that there is a fault in the switching circuit. Look for a break in the wires. Check the wires where they join the bottom of the control knob shaft - I have never known one to fail here, but you never know.
You need to definitely prove if the ignition unit is generating a spark tic. If it is not, then you need a new ignition unit.
If after changing the battery and operating the switch you are definitely generating a tic, but the fire is not lighting, then the most likely problem is the spark wire that goes from the igniter to the burner - item 42 to 41. After many years this wire gets old and the insulation can break down, and the spark can escape to chassis in many places. Sometimes if you listen very closely you can hear a very weak tic tic but the fire will not light. This is a good clue that the spark lead is broken or worn - it is shorting out before it reaches the burner. But it is important that you prove which is faulty - the ignition unit, or the spark lead - because changing the ignition unit is easy, but will be no good if the spark lead is faulty. Changing the spark lead is more complicated, so you must be sure that is the problem.
Changing the spark lead is a job for an engineer or a very keen DIYer. It's not rocket science, but you are dealing with gas and fumes, so you must either be competent, or don't bother.
NOTE - the drawing below is for a double burner fire - the single burner models are the same in principle.
The sequence of events is as follows. Remove the chimney pipe - item 1. Undo the lock ring and pull the pipe away. There is a silicone O ring that seals the joint. This a safety critical component and should be replaced - order one at the same time you order a new spark lead - items 8 and 42. Disconnect the gas feed pipe - if you don't know how to do this safely and competently, then you shouldn't even be attempting the job. Then remove the screws that attach the fire base plate 12 to the wooden plinth. The whole fire should now lift up and out. You are looking for the burner box 44 that protrudes down into the open below the van - either a single or a double depending on your fire. Clip 46 releases the cover and gets you inside. Then it should be obvious where the spark electrode 41 is, and trace its feed wire 42. You should see where the problem is - quite often I have seen the wire just crumble to dust. You can make your own DIY wire if you are competent, or order one. Make sure you have a good spark before re-assembly.
Also take a good look at the burner assembly 37 - they are not expensive and it is usually a good idea to replace the whole thing if you are ordering spares. Have a good dust and general clean up while you are in there.
Once you get the thing in bits, it's all reasonably logical. The awkward and dangerous bits are the chimney joint and the gas connection. The silicon O ring is essential to be properly placed - it stops fumes from escaping the joint and into the van. And as already stated, the gas connection is an obvious point of danger if not done properly. Do not undo and redo gas pipes unless you have learnt the proper protocols.
