As an interim measure (not sure how long you are talking about though), why not just get a couple of cheap electric heaters and use the immersion on your tank
Not perfect, but not bad
Not sure I'd use eBay to find an installer for a new boiler though. He's not exactly got 100's of eBay feedbacks for boiler installs. I'd ask friends and family for recommendations
You mentioned that you didn't get the installer to fix the leak, did he offer! Why not?
How long after the install was the leak sealer put in?
I think we need all the facts before we Slag off the installer
Not really possible to over tighten them, doesn't need to be clamped down too hard though.
Make sure the cistern is centered properly as well
Good luck
Try - Apply a little silicone sealant to the pan and position the donut in position, leave to set for a little while. Apply more silicone to the top of the donut and position cistern. Tighten bolts to fix cistern in position
You 1st need to measure your incomig supply, it would be pointless installing a combi capable of supplying 15l/min if your mains supply isn't up to it.
Ps - get your installer to check the pressure too
Good to hear he honoured his original quote. If he quoted a price and didn't do extra work, then I don't really see how he could do anything else, the fact it took him longer is really his tough luck