This is a very basic water heater and it will be obvious what is wrong, as it is a new installation i would check the flue as it is this that causes the most problems, also check that the working gas inlet is 20mbars other wise when the boiler lights up there is not enough gas to keep the pilot alight. Phone the installer to check the installation then phone the manufactura to get one there own engineers out.
andy the gas man
July 2008