Webasto Airtop 5500, any ideas?

[Nauti Fox]

It started to play up a few weeks ago, the odd cut out while running, but no fault codes.
Then it took more start up cycles, ending up needing three or four before it would go, although every time it would light up and produce heat before shutting down, again no fault codes.
This was using setting two out of three on the control, eventually it got to five tries so I thought I"d better have an external look. Couldn't find anything wrong with the feed etc.
I thought it might be the flame sensor so was going to take the unit out, thought I'd try it on setting 1 which they call eco.
Fired up straight away and ran several hours until I shut it down. Did the same the next day and no problems on the eco setting.

It now runs fine on all the settings.....
Any explanations you can think of?

 

[dgadee]

My experience (slowly gathered) is that an awful lot of problems with devices on board are due to bad connections. 12 volts seems to be a disaster area for this. E.g. I have surmised that a water pump for the freshwater which played up for a month was just down to a bad connection - it started to work again after I was sorting something in the switch panel. I would go over your connections.

 

[pagoda]

My experience (slowly gathered) is that an awful lot of problems with devices on board are due to bad connections. 12 volts seems to be a disaster area for this. E.g. I have surmised that a water pump for the freshwater which played up for a month was just down to a bad connection - it started to work again after I was sorting something in the switch panel. I would go over your connections.

Most of the connectors at the heater end (we have an AirTop5000) are quite well protected- rubber cuffs etc. I'd check the main fuse and wherever the power for the heater is fed from? That might be ordinary spade connectors? Exposed?

Our AT5000 stopped firing -without any flashing error codes- and further investigation discovered the burner metal gauze clogged up with congealed carbon deposits. We replaced the burner gauze and cleaned out the combustion chamber before re-assembling. (cheaper than entire burner!) Many of these heaters are used in trucks. The market for parts in businesses dealing with trucks is more competitive than for marine users- so you may find better parts deals there.

 

[BlueChip]

I'd second that this is due to a fuel problem, but I'd check the pump before opening the heater chamber.
Do you have a pre-filter on the pump? If not then I'd recommend you fit one immediately, then check the inlet to the pump, this has a tiny aperture and is susceptible to blocking up. I had years of intermittent problems with my Webasto Airtop 5000 before I discovered the cause of the problem.
The heater would burn for days and then one day would just shut down when ramping up, it turned out that there was a minute amount of dirt in the pump. Westerly who factory fitted the heater didn't fit a prefilter.
You can take the pump off, poke about in the inlet, bang it down on a firm surface and try and dislodge anything in it, then drive the pump using a 12V on/off supply for long periods using kerosene and solvents through it to clean it thoroughly.

 

[Nauti Fox]

Thanks for the comments, I've checked connections, the fuses and holder, all seemed ok and a multimeter showed little resistance between the fuse holder and the main plug.
It does have a pre filter and clear section of hose either side of the pump, all looks well there.
I did consider the gauze but I can sort of understand how running it in the eco mode allowed it to spool up as it doesn't run as fast, but not why it now works in all modes again. I would of thought running at a slow speed would add to the carbon deposits?

 

[BlueChip]

Check also for dead volume in the inlet fuel pipe connections, even the slightest air bubble in the connections can play havoc, its important the ptfe fuel lines but up close to each other.
These random problems are a nightmare to diagnose.

 

[pvb]

I'm surprised there was no fault code flashing, my AirTop Evo was very good at delivering fault codes when the burner coked up recently.

Incidentally, you say it's an AirTop 5500 and not an Evo, but I didn't think there was such a beast.

 

[Nauti Fox]

I've got a nagging feeling you are right and it is a 5000......with a 5500 manual..don't know why, it came with the boat

 

[pagoda]

I've got a nagging feeling you are right and it is a 5000......with a 5500 manual..don't know why, it came with the boat

The identity / serial of the heater is on a black sticker on the outer cover - but there's an excellent chance that is almost impossible to get at to read!

 

[Nauti Fox]

Ah, even more of a senior moment....it is an evo...oh dear