I am fitting a shower pump and want to install a Surrey flange to the top of the HW cylinder but the existing nut on top of cylinder won't come loose - it's in good condition and not corroded. Have tried sustained force against wrench, hammer blows to wrench, heating the nut, applying lubricant etc but it won't budge. Don't want to damage cylinder by using excessive force. Any help in solving problem very much appreciated.
If all fails and I can't install the Surrey flange what problems would I have by just taking the hot feed to the pump from the existing pipe out of the top of the cylinder?