Along with Jrb and Sir Miles, I wouldn't trust it. It MUST be fitted by a gas-safe registered fitter and be certified. If the installer has got this small/simple detail wrong, what else have they cocked up? This is not the sort of job to be done by amatuers. Carbon Monoxide is a silent killer and I'm sure you saw what happened to that row of houses in Irlam... Your landlord needs to sort it NOW, I'd get on to trading standards etc if he doesn't (and if he does, check out the plumber's credentials for yourself, see the link below)
http://www.gassaferegister.co.uk/
http://www.gassaferegister.co.uk/
