Webasto Airtop 3500 flame failure

[Plevier]

My Airtop 3500 (year 2008 - does that make it a 3500ST? Not sure of the difference, not got the unit or the boat documentation in front of me) has started failing on start up with error code 2 which means flame failure, even though you can feel slightly warm air starting to come out of the vent. Generally you have to switch off and restart once for it to go, occasionally twice. Very occasionally it goes first time! The pump is ticking away happily and gets up to full rate before the shutdown happens.

I see from a downloaded manual that there is no readily accessible glow plug and gauze to clean as on an Eber, it's a much more major strip to get at the glow pin, which I gather doubles as the flame failure detector. It's also quite an expensive bit if it needs replacing!

I'm quite prepared to do the strip down if necessary, would just appreciate any informed advice ahead on whether doing this and cleaning is likely to cure it, and what are the chances of needing a new glow pin?

Thanks

 

[RAI]

When mine failed in the same way, it turned out to be dirty fuel. The fuel bug bakes onto the evaporator until it no longer works. When I was struggling with it, Webasto did not sell the evaporator gauze disc separately and the whole unit was expensive. I ended up fitting a proper CAV engine fuel filter into the supply line. The little plastic filter provided is not up to much.

 

[David2452]

Probably overdue for a service, the plug is a combined flame sensor and glowpin, nothing like the Eber, STs were a short production run and are quite rare in the marine world unless somebody has bunged a vehicle one in, but are easy to identify by the label. The internals are quite specific to the ST, they have a square glowpin /flame sensor and a different burner, air motor, overheat sensor etc. I have one in my own boat and they are a great heater but they are not fit and forget and need regular service just like your motor.

 

[Plevier]

Thanks David. By overdue for a service, do you mean stripping and cleaning as I have suggested? Does the plug need replacing routinely?
The repair manual says "The heater requires no servicing." (which I found amazing!) It does then go on to list some external visual checks, but nothing internal at all.

 

[David2452]

Yes, by a service I mean a strip and clean, but it doesn't stop there really, the peramiters need checking against spec and the burner not infrquently needs replacing, be very careful with the pin as they are ceramic and never test it by applying current direct as the ECU sends a pulsed current to it not a permenant one. Make sure you get the exhaust CO2 checked when you have finished to make sure it has a good clean burn.