Job ended up costing in the region of £1000 for just over an hours work. When we had to get someone else out six weeks later (As the problem persisted) we discovered the parts we were advised needed to be changed weren’t changed but instead new washers were installed as a stop gap repair and the the part itself was still under warranty.
Had the repair properly completed a few months after which costed us a further £90 (plumber ordered part under warranty and installed)
In addition to this, be very careful as you will be charged per inch of tape he has used. This will all be added as he’s finishing up on the job and you will not receive forewarning (other than stating costs for labour only) this statement generally doesn’t include things like washers/screws etc. as stuff like that is generally a pre requisite.
Ending up adding about £85 after payment, stating that this was for the washers that had been installed.
Thankfully we now have a fully functioning boiler which does not leak.