Truma Combi 6 not starting (solid red light)

[driftwood]

Hello everyone, I'm new here and am looking for a bit of wisdom.
I have the above Combi 6 (non electric). Has worked no problem for 10 years, Over the last year it started acting up, always the same fault. but with numerous attempts at starting or sometimes changing the bottle, she would fire and stay going, then might not happen again for a few weeks, gradually it became a more common problem untill now, it has given up.

Symptoms: Turn the knob to on (any position, hot water or heat or both same result). hear a click, recirculation fan kicks on, combustion fan comes on, a few seconds later, everything off and solid red light on the selector. The manual says its a gas issue or perhaps blocked intake/exhaust.
The PCB fault code says different-ssssslls-combustion motor current too high.

What i've done so far: removed all the ducting, cleaned both fans of dust, replaced the ignition transformer, replaced the regulator, replaced numerous bottles (fridge and cooker work fine), inspected the wiring no chaffing, confirmed gas flow to the unit,

fault code says the motor but it spins freely? has anyone had this problem? another question i have is should I be able to hear the igitors firing/clicking? Could someone start and check in what sequence they hear the various sounds please? I have switch on-click from boiler(gas valve relay?)-recirc fan on-combustion fan on-shutdown. The whole process is about 30 seconds. does the ignition kick in after the combustion fan or before?

Also I know its impossible to find but if anyone has worked out the wiring to the combustion fan? 4 wires pos/neg and I presume some sort of feedback wires related to the start seq.

Anyway, Thanks for taking the time to read this and if I work it out I will post the solution.
Happy camping

 

[Richard n Ann]

If it wasn't for the fault code I'd be thinking thermocouple.
Have you got a clamp meter to measure the motor current?

 

[Winger]

If changing the gas bottle in the past helped it may be the gas regulator that is the problem. Cheap to switch and try before you start ripping things apart.
I’ve read on different posts here that regulators on some systems can get gummed up

 

[cyberyacht]

If it was the regulator, the oven and fridge would be playing up as well.

 

[meanders]

If it was the regulator, the oven and fridge would be playing up as well.

Not necessarily. When ours failed in the old van, fridge and oven worked, lighting the hob or gas fire was a different story.

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[driftwood]

I replaced the regulator, also I have 3 different gas bottle with separate hoses so I don't suspect blockage, the hob fires up nice and strong. I'm suspect of the gas valve on the unit not sure if its opening, I hear a click like a relay at start but no clunk like a solonoid valve being energized, Is there anyway to test this? There are 3 wires to each solonoid I presume it should be no resistance through the coil (2 wires) and perhaps one is a sense wire? I'll check that later, not sure where the valve sits in the startup sequence.
With no ignition clicking sound this is why i replaced the ignition box but still no sound, I'm leaning towards the ignition electrode kit in the burner, perhaps they are worn/damaged and not firing so light up is not being seen.
I know the fault code says the fan but I'm a bit suspicious of this as it spins freely although as Richard said without a current meter I can't be sure.
Can anyone tell me if they hear the gas valve clunk before or after the ignitors start clicking? or anything about the sounds in the sequence at start up?
I'll do some more wiring checks tonight.

 

[Lenny HB]

If it was the regulator, the oven and fridge would be playing up as well.

They will work fine normally when a regulator is gummed up as the flow rate required for them is much lower but it won't be able to supply the high flow rate the Truma heater requires.

 

[driftwood]

My guess would be that the sequence should be something like this:

switch on-relay click to energise the gas valve primary (clunk)
-recirculation fan starts
-combustion fan purges the chamber and brings air into burner
-ignition (rapid clicks)
-light-up sensed by flame sensor in the burner
-gas valve secondary opens for full supply (whoosh)

This is purely what I'm guessing, hence why my suspicion goes right back to the valve or ignition probes.
Anyone elses thoughts on this would be much appreciated

 

[GeoffnDee]

driftwood I do not know if it would be any help to you , but if you google truma combi installation manual the truma.net which although the USA version has , on page 28 , a connection diagram for the 12v Control PCB which may be of some use.

 

[driftwood]

Ill look it up thanks, I'm gonna get the multimeter out tonight and con check the wiring

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[Burgo]

A swift Google gave the following; maybe the same? https://motor-roam.co.uk/truma-trumatic-c3402-boiler-inspection-troubleshooting

 

[driftwood]

Sorry about being so long in coming back to this. I had it on the long finger, I replaced a zenor diode and the schmitt trigger on the pcb of the combustion motor and now she lights up again - happy days, so i suppose the moral is the fault codes do point to the correct issue at least on this occasion, If you have the same issue its your combustion fan motor-very pricey! I hope this thread may help someone else, best regards, and thanks for all the help folks.

 

[Dave Scadding]

I had a similar problem. The cure for mine was the outer exhaust flu pipe. There is an inner exhaust and an outer intake. I found that the outer flexible pipe doesn’t want to be clamped down tightly, when I slackened it off leaving a gap where it exits the van to the external Truma outlet everything works. If I tightened the pipe to form a seal I kept getting red light. I guess with it being slack and with a gap it can draw more air in. Anyway it worked for mine.

 

[driftwood]

I had a similar problem. The cure for mine was the outer exhaust flu pipe. There is an inner exhaust and an outer intake. I found that the outer flexible pipe doesn’t want to be clamped down tightly, when I slackened it off leaving a gap where it exits the van to the external Truma outlet everything works. If I tightened the pipe to form a seal I kept getting red light. I guess with it being slack and with a gap it can draw more air in. Anyway it worked for mine.

yes that can happen, but I had removed all my ducts to rule that out, ultimately it took a year of playing around, but I believe I had a dodgy schmitt trigger when you look at the pcb on the combustion fan its the black chip, unless your set up for soldering its a no-go. Your advice is sound, I would recommend people to try everything first before investing in a combustion fan. but unfortunately it seems once the usual suspects are exhausted your snookered, hence the reason it took me a year to solve.

 

[RonnieC]

Sorry about being so long in coming back to this. I had it on the long finger, I replaced a zenor diode and the schmitt trigger on the pcb of the combustion motor and now she lights up again - happy days, so i suppose the moral is the fault codes do point to the correct issue at least on this occasion, If you have the same issue its your combustion fan motor-very pricey! I hope this thread may help someone else, best regards, and thanks for all the help folks.

Hi driftwood, I have the same problem on my Truma combi 4e, "current for combustion air motor too high" error. Could you show in a pic where the zenor and schmitt trigger are on the board. I'm an electrician so reasonable good at soldering and would like to have a go at repairing the board before purchasing the expensive replacement. Many thanks for your trouble shooting skills!

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[Burgo]

Ours sulks if we turn the gas off while it's still switched on. It's then a mare to get running - throws a red light for a couple of goes.
For us the answer seems to be to give it a more controlled shutdown, by turning it off on the dial of eternal confusion, letting it shut down in a orderly manner (if it was firing at that time) then turning the heating gas bottle off.