Pulsa Coil A Class off peak power relay burnt out

Please help! Our Pulsa coil A class has just gone out of warrenty and decided to stop working. We've had a local plumber come out to look at it and he advised us the off peak power relay has burnt out and not safe to use. Saying that a few days before it broke down there was a very strong burning smell coming from it! However he said he couldn't fix it and we would need to contact Gledhill themselves, when doing so they wanted £340 to fix it! Please could you advise what the going rate is to have this problem repaired? We've had a little look at a link you posted on this forum and it seems the part is only about £30.

Many Thanks