Ken:

I have my VW manual (pre-Bentley, 80-81 Vanagons) and there
are 9 pages on the aux heater (gasoline), with location of
parts, test procedures, etc, including the two page
troubleshooting guide.  Also the wiring pages.  i don't
know if all this stuff is in the Bentley.

I think, but may be wrong, that the gas and diesel models
are really pretty much the same.

If you don't have this info, I'd be happy to copy it and
mail it to you.

Here's the operating actions as I understand them.  When
turned "on" by the knob or timer function, the blowers
run at 1/2 speed.  That means the fuel is injected at
1/2 speed.  The glow plug/spark plug is powered.  When
the unit starts heating up, the flame switch "sees" it
and then the unit goes to full speed blowers/fuel.
I think(!) if the flame switch doesn't detect ignition,
the safety switch shuts things off between 150--230
seconds

If the unit gets too hot, the overheat switch shuts the
unit down.

The temp sensor turns the combustion blower/fuel pump
circuit on/off to maintain temp as set by the position
of the knob.

The manual states that the unit should ignite within
70 seconds and shut down within 80-160 seconds (at
68 F) or the flame switch is bad.

None of this exactly matches the symptoms you described, but
I hope all of this helps.  My '81 has worked perfectly except
for about year 2 when the overheat switch failed.
One mechanic around here told me a while back that mine
worked so well because I used it a lot--lack of use
led to failures.

                                Richard A. Jones
                                '81 Vanagon  Mr Bus