Starting on LPG

When I got my van I was told to start up on petrol and switch it over to LPG once it had warmed up, I kept forgetting to switch it back off before stopping and have found that if it's not too cold out it starts fine on LPG .... But... Will this cause me problems? Is there a good reason why I should start up on petrol?

Starting on LPG is supposed to cause engine damage in cold weather which I take to mean below freezing. I believe it is because the fuel doesn't vapourise properly until the engine has warmed sufficiently.

However, there should normally be a setting to allow it to start on petrol and then automatically switch over to LPG at an appropriate time. Time to investigate the handbook / guarantee documentation?

LPG is measured as a gas (like how you have jets in a carb, we do it to the lpg gas). Gases change size alot through temperature. So we try to keep the vaporizer at a static temperature to keep the gas measurement accurate. Starting the van cold on lpg means the gas will be not be injected at the correct ratio.

Hmm, ok, well I'll Try to remember to switch it over before I start up,at least it doesn't seem like a drastic problem if I forget! not on gas at the mo cos the tank looked a bit rusty and thought I'd give it a clean and paint before I fill it up again

If you have a injected system, LPG ECU corrects injection timing to reach the right air-fuel ratio.

In lambda controlled aspirated systems same thing happen.

In old style aspirated system, your A/F ratio can become too lean.

Maybe it can give you some driving problems, but engine don't have damage (if engine is cold, kat is cold, and it can't ignite unburned LPG).

Theoretically is better to heat engine on petrol for a lot of reasons, but I see with my eyes cars that runs everytime on LPG, even during cold starting at -10°C, without problems for hundred thousands kilometers...
Surely you must allow engine to heat a bit at idle before driving if temperature is very cold.