Heating problem solved - and maybe a new problem

I bought a Mr. Buddy propane heater for the temporary greenhouse this year - it runs off a 20lb tank of propane.   It has a low-oxygen sensor, because it was designed to be used indoors, though not in tightly sealed rooms.  From looking at the design, I'm pretty sure the shutoff mechanism uses a thermocouple.  If the O2 concentration falls below a certain value, something like a pilot light flame becomes smaller and this shrinking cools a nearby thermocouple, which triggers shutoff.

The reason I'm trying propane is that my electric utility heater is very expensive to run.  My problem has been that the heater has been running for 4 hours or so, after which the heater is going to auto shut-off mode.  I speculated that there was local low O2 concentration near the mechanism because air flow was too low.  To test this hypothesis I bought a small fan and placed it near the heater.  Last night the heater ran for 12 hours, so maybe the problem is licked.

But I am a bit worried about bud blast from unburned propane or perhaps a byproduct of burning?  The buds on that C. labiata 'Tipo' don't look right to me.  They're paler and stippled, though that is hard to see.  But its a bad sign.

I think I'm looking at a total loss here - always tough to stomach when a plant blooms only once per year.

I am reading conflicting reports of the effects of burning propane.  Some sources say "no problem" while others say with great certainty that burning propane will blast your buds!  Thing is, this heater burns with nearly 100% efficiency and the auto shutoff should have disallowed unburned propane from entering the greenhouse.

Alternatively, it is possible that bud blast results from temps on the low side - but I've been good about maintaining the greenhouse temp.

I favor the propane explanation.  If that is correct, I'll have to deal with the cost of electric heat and just keep the propane heater for emergencies.