webasto won't restart

[David Anderson]

I'm in Cloudcroft and my webasto will heat up to the burner's upper limit as it should and cycle off.  The fan heaters continue to run as they should, but when the coolant reaches the lower limit the burner does not come back on.  The fans run until the aquastat senses the coolant is too cold and the fans shut off, the pump shuts off, and the system shuts down.  I can turn the "system switch" to Off and back to "system heat" and the pump will come on, the heater will light and the fans will begin to blow as soon as the aquastat senses hot enough water.  The cycle keeps repeating itself.

Where do I begin to look to diagnose this?

David

[Sean]

Usually this is a sign of a sticky relay in the Webasto control box.  However, I have also seen this symptom with a partially obscured flame sensor.  I would start by cleaning the flame sensor and the nozzle before trying to diagnose a finicky control box.

-Sean
http://OurOdyssey.BlogSpot.com

[David Anderson]

I had time to tinker with it Friday.  I did two things- burped the heater unit and removed my 10' pipe/upstack.  I drained the coolant about a month ago and I cannot remember if I burped the heater when I recharged the system.  It may have been getting a signal to the overtemp sensor and cutting out. 

I had all the heaters running, set at 90 degrees and it never cycled off the high temp coolant limit.  I kind of think it may have had an air lock   We drove 500 miles yesterday and 150 today and made it back home.  I will look at it again Monday when I have time.

David

[luvrbus]

I found a bad circulation pump will cause that also David

[Sean]

...  I kind of think it may have had an air lock   ...

and

I found a bad circulation pump will cause that also David

In my experience, an air lock or a bad pump (and an air lock often quickly leads to a bad pump, if you have the style that can't be run dry) will prevent the aquastat from ever turning the fan coil units on.  Yet you said the fan units are running normally, which suggests you are getting some coolant flow.  It's possible that the pump is just bad enough (or a line is just obstructed enough) to allow enough flow to turn the fans on, but not enough to prevent the burner from overheating, but that's a less likely fault scenario.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[David Anderson]

When I bled the unit I really saw no air escape.  It looked like 100% coolant, however, I ran it for 30 minutes after that at 90 t-stat setting and it never turned off.  I had to return to work.  It seemed like before that purge it was cycling too early, ie., not getting warm enough.  This time the heater air felt really warm and the coach temperature was rising rapidly. 

6 years ago I kept having a smoking problem at high altitudes.  It was so bad the burner chamber would carbon up clogging up the burner.  I cut my exhaust pipe from approx 20' to 3' and have not had the problem since.  Sure Marine suggested this fix.  I only use a 10' upstack when around other coaches.  I'm not sure if this is a problem or not.  However, like my original post, I did two things simultaneously which resulted in a change in the heater operation. 

David

[David Anderson]

I just read the thread on BNO-- "Webasto Question".  According to Geoff's post the overheat fuse is a one time fuse, so I guess my unit was not cycling off that circuit because by me resetting the "system switch" the unit would come back on and run.  Somehow the high limit cutout switch was sensing warm enough coolant to cycle, but not allowing the unit to refire after the water cooled down below the low temp limit.

David

[Sean]

I just read the thread on BNO-- "Webasto Question".  According to Geoff's post the overheat fuse is a one time fuse,

There are actually two types, a one-time, and a manually resettable style.  (If you blow the one-time, I highly recommend you replace it with the resettable type.)  Neither will produce the symptoms you described, which is why I did not suggest checking the thermal protector.

so I guess my unit was not cycling off that circuit because by me resetting the "system switch" the unit would come back on and run.  Somehow the high limit cutout switch was sensing warm enough coolant to cycle, but not allowing the unit to refire after the water cooled down below the low temp limit.

The thermostat (which you are calling a cutout) alone will also not produce this symptom.  It is a mechanically simple device; there is no way for it to "stick" in the open position as you described.  It will either be stuck open full-time, which would mean the unit would never fire, working normally, or stuck closed full-time, which would cause the thermal protector to blow.

This is the reason I first suggested that you have a control box issue.  The thermostat feeds a relay in the control box, and that relay, unlike the thermostat itself, can stick.  The control box is also designed to prevent the unit from restarting (until power is cycled, as you described) when it detects an error, for example, if the flame sensor detects loss of flame.  Since a dirty flame sensor can produce this error even when the flame is burning fine, I also suggested cleaning the sensor before troubleshooting the control box.

-Sean
http://OurOdyssey.BlogSpot.com

[Geoff]

I just read the thread on BNO-- "Webasto Question".  According to Geoff's post the overheat fuse is a one time fuse, so I guess my unit was not cycling off that circuit because by me resetting the "system switch" the unit would come back on and run.  Somehow the high limit cutout switch was sensing warm enough coolant to cycle, but not allowing the unit to refire after the water cooled down below the low temp limit.

David

If you found my old post then you must know that I had a similar problem and turned out to be the control module.  Mine is working like new again with the new (good but used on eBay) module.

--Geoff
'82 RTS AZ

[David Anderson]

I cycled it with the high temperature cutout 2 times today and it worked fine.  I then let it cycle with the t-stats in the coach 2 times and it worked fine.  I guess it's self healing  

Anyway perhaps some cleaning may be in order.  I cannot get it to duplicate its failure that took place in Cloudcroft.

David

[luvrbus]

The problem with Webasto's  is they never work when needed David lol

[David Anderson]

The problem with Webasto's  is they never work when needed David lol

I have had my share of this in the past    However, when it works it is the best heating system available.  Quiet, no smell in the coach (can't say that for the neighbors though, cough, hack ), efficient, and I love the free heat running down the road.

David

[David Anderson]

Bump

This is a continuation of an old problem that reoccurred again last winter, and I know it sounds silly, but due to all the stuff I've been doing, (building my shop, building my son's house) I have not had a chance to tear into the Webasto to fix it.   Well I finally jumped in.  I took the unit apart, cleaned the burner chamber, cleaned the flame sensor and the ignitor, and changed the nozzle.  I replaced the Perry filter on the water loop.  After all this I fired her up and ran it for a couple of hours getting it to cycle at least five times.  It never smoked and purred like a pussy cat the whole time.  It ran great.  Now, hopefully this winter it will work ok.

I did notice that the burner tube was a bit deformed and not round.  I straightened it out some to make it more round and reinstalled.  Should I have replaced it?  Not sure.

I hope I'm good for the cold season.

David