Looks like builder lied. What can I do.

[loosenknot]

Very difficult build. Architect issued practical completion last week so I owe the builder 2.5 per cent. today I decided to double check the boiler and heating with a gas safety engineer as I’ve been having problems with the radiators. (Every other service I’ve double checked has been faulty).

The engineer found that the boiler has been installed against manufacturer recommendations, thus voiding the warranty. He said I have to move the radiator down to get adequate clearance (there is currently none). He also found that the boiler and water tank have not been earthed and there was some sort of required switch missing along with several certificates. He suggested that the whole system had not been flushed (the radiators at the top of the house don’t heat up and Hadn’t been bled). It will cost a couple of thousand to fix

Worryingly it turns out that the installer - hired by the contractor - had ticked yes on a form in the boiler book to things he hadn’t done and was meant to do ... earthing, flushing etc ie he has lied.

The entire system was then checked and signed off by a gas safety engineer ... (which then meant the building control signed it off). And the gas safety engineer who stated that the system was compliant and passed all the checks? the contractor.

In addition: The gas meter has been relocated outside the house and for months I’ve been asking the contractor for the key to open it up and he keeps saying he hasn’t got it or it’s on the table. My alternate engineer today had a spare key and opened it up. There was a warning notice left by the gas board tied to the gas meter saying that the system had not been earthed and a competent gas person would need to do this ASAP.

Under My building contract the contractor is meant to fix his mistakes in this snagging period. However as he has lproven incompetent do you think I am within my right to ask someone else to resolve this and then deduct the cost from the money owed? Also can I withhold the money I owe him even if pc has been issued until this is resolved?

Don't pay him a penny more! Not only has he left your house in a dangerous state (knowingly, by the sounds of things), but he's actually invalidated your Building Control consent. Send him the report from the person who checked the boiler today, a screenshot of the fraudulently ticked form and a pic of the warning notice on the meter and tell him you want a refund on what you paid for all the plumbing work. If he kicks off, threaten to sue.

Don't pay the snagging until it's done, but the builder has to be given the opportunity to put things right.
Your architect should be going through all this with you not random people online though, that's what you pay them for too.
I'm surprised there's no retention period, we had 12 months to make sure no issues regardless of the weather or temperature, then paid the final percentage.