HI
get few quotes because one agreed many roofs are not done right and will create all sort of problems.and try to get someone who has reputation or is known as doing a good job even if you have to pay few hundred more.good luck
HI
4v is acceptable it does not have to zero all the time.should be 240v at the boiler.if less than this then the fault is external.check all external fuses again.
HI
Never heard this before.you are right the glass is factory fitted and should not come out.check the rubber seals for evidence of tampering.contact manufacturers see if they can help.