I turn on the heater it starts but goes of after about 30 sec

whatever problem you are having with brivis buffalo, the first thing you need to try is RESET. This is how you reset.
1. turn off your heater from wall switch for at-leat 5 sec
2. turn on your wall switch for 5 sec
3. repeat step 1 and 2 for atleast 3 times within 60 sec

my brivis buffalo 20 was keep turning off after 30 min. RESET fixed my problem

I would guess its possible that the cable that closes the flap under the hood could possible be failing.

Sounds like your thermocouple is shot.It's that little tube that the pilot light heats up.I am assuming that you have started this heater before.The thermocouple has to stay a certain temperature to keep the gas flowing.You can buy universal thermocouple kits at your local hardware store.Make sure gas is turned off.Loosen the coupling nut on the outside of the tank then remove the tin and remove the heating part.The whole thing is a small 1/8 tube.Bend new one like the old one and put it back in place.If the kit has yellow Teflon tape wrap the threads on the coupling and tighten.Turn the gas back on and test for leaks with soapy water.Thanks for choosing FixYa.com.

I always add this for your information. If this is not the solution that you are looking for please re post because when we pick a question to answer FixYa takes it out of the questions.

If the gas valve is getting 24 volts and still not responding then replace it. If it is not getting 24 volts then replace the circuit board.

using the key,lock car/hold key over for 30 secs,then press/hold unlock button for 30 secs,that resets the alarm/immobiliser.OR does the pre heater coil light up orange then go out so that you can start car,or are you trying to start the car too soon or waiting too long after the light goes out.also try spare key,sometimes key looses code...as the pre heater is operated by opening the drivers door any delay...
have you tried wynns/redexe diesel treatment,could be dirty injectors.....
after trying all the above and you have no joy, come back to me, ta!

sounds to me like your check valve in fuel line is not working. If you have the original lift pump it located in there.

you should hear a click ,its the valve opening ? of check to see if the air fiter is clean ,

I had the same problem. I took the nozzle head off and blew through it with air. I also blew through the air line, this is the one that goes to motor. It has worked fine ever since.

Roscoe007 shouldnt speak unless he knows what he is talking about, as a heater installer i am telling you the ignitor needs to be replaced, the very fact that the ignitor does light for about 30 sec than goes out rules out any issue with the themostat, replace the ignitor!

I had a similiar problem... I had to replace my bulb, which means $$$!