Hello Maureen and Steve,
I must agree with Peter that you have a gas leak. That is assuming that you started on a full 11kg gas bottle.
The calculations below would confirm that even if your thermostat was faulty and the fridge / freezer remained on full-time with both doors open, it would be impossible to deplete a full 11kg bottle in just two days.
The fridge is rated at 170 watts on both mains electricity and 12 volt battery. One would assume that the gas jet is designed to produce an equivalent amount of heat, in which case this would be measured as 0.621 mega joules (pronounced mega jewels). About the size of a gas pilot light.
1 kg of gas is 1.96 litres in LPG which has the capacity to produce 49 mega joules of energy over the period of 1 hour.
Therefore the fridge consuming 0.621 mega joules would last for 78.90 hours on 1 kg of gas.
Assuming that an 11 kg bottle is full to 80% which is 8.8 kg, the fridge would run for (8.8 x 78.90) = 694.32 hours, meaning 28.93 days.
Bearing in mind that both fridge and freezer doors are closed and the thermostat is normally working as expected, this figure of 28.93 days could easily be doubled.
All of the above assumes 100% efficiency which is not the case, so allowing 10% for inefficiency; the figures are not going to be drastically different. Without checking the specification of your particular fridge, I can confidently suggest that the majority of modern 3 way absorption fridges are reportedly 93% efficient whilst on LPG.
We have been through this calculation many years ago and it was confirmed by a member who rarely washes (in the van I might add) and rarely cooks in the van, who stated that he has had fractionally more than three months of continuous use of the fridge on one 13 kg bottle of propane. Admittedly, it was the smaller fridge with the freezer compartment within.
Conversely, if you had a flame to the rear of the fridge which was capable of burning 431.2 (49 x 8.8) mega joules of energy over a period of 48 hours, equivalent to 119.77 kilowatt hours, not only would you have seen and heard the flame, your van would now be cinders.
119.77 kilowatt hours would be similar to exposing the surrounding materials to the flame(s) of two and a half motorhome gas ovens for a period of 48 hours.