Who pays a bill that is too high due to a known fault in rented accomodation?

I moved into new rented accomodation in january. the first gas bill came through after a month and was sky high. we went to go and read the meter and the meter reading was even higher. so i called out the gas man suspecting a possible leak in the line. he checked it and said that there wasnt however if a boiler isnt operating properly it will use up a lot more gas in order to achieve the same effect. well our boiler wasnt working properly and had already mentioned this to the letting agents of which they did nothing about. after i mentioned it to them again they sent out somone to service the boiler. this happened, the boiler worked for about a day and then the flame wouldnt start up again so no hot water now. said something to the letting agents again so someone else came out again it worked for a couple of days then wouldnt work at all and now started gurgling. someone else came out yesterday and now the boiler seems to be working. but what i would like to know if anyone can please help me is do we have to pay the skyhigh bill or is that on the letting agents or even the landlord? the letting agents are saying its nothing to do with them.