Thanks for your enquiry.
I am afraid that you have no claim against the Seller for the gas leak or the cost of repair. As a Buyer, it is a case of "caveat emptor" (Let the Buyer beware) and you therefore have to satisfy yourself before completion that you are happy with the state and condition of the property and its appliances.
I am sorry this is not the answer you were looking for, but it sets out the legal position.
I hope I have assisted, but please let me know if you require any further clarification.
Did the Property Information Form state that the boiler was in good working order?
Thanks for your reply.
The principal rule is still that it is up to a Buyer to get everything checked before completion.
However, the Property Information Form (PIF) does form part of the Contract and a Buyer can sue a Seller for any fraudulent answers.
Unfortunately, it is very hard practically to sue a Seller in such a position as you need to prove that he has deliberately lied in his answer on the PIF and if you have the evidence, you would then have to issue Court proceedings and prove your case. For the cost of the repair, it probably isn't worth your while.
What I would suggest you do is to get your Solicitor to write to the Sellers Solicitor, with a copy of the British Gas invoice and ask that you be reimbursed. The Seller may agree to pay willingly, but if he doesn't you would have to go to Court to pursue it. Most Solicitors are happy to write one letter in these circumstances, so it is worth a go.
I hope this helps.
All the best