Mmmm, I agree. You shouldn't have even attempted to open the combustion case. It maybe a water carrying part but you're not qualified to crack the combustion covers seal.
First point of call when it comes to a boiler is find the yellow pages or get onto google and find a company or engineer...
Remove the radiator, take a bucket or large pot and hold it under/in front of each rad valve and open it up again slowly, see if you get a good pressure and constant flow out of it. I'd suspect there's a restriction in the pipe. A flush machine could loosen it but at the same time BG does note...
A full strip down and clean is the only way to sort out a 3 way on these boilers, sometimes find they become jammed in place, no amount of cleaning solution will sort that little problem, it requires a good scrub or a new innards and new O-rings. The kit is cheap :wink:
A filter will help...
It can be boxed in without vents, but I wouldn't fit a complete top and bottom. Leave a good air gap around the case, also the build the cupboard so it's fully removable, these boilers need good access at the bottom
The old stat will have a live, neutral and a call wire.
Your new programmer doesn't need a permanent live. It's battery powered so it's happy days. The boilers old clock needs to be either bridged out or set to constant.
Most battery powered stats only have two terminals, live in and call...
Any dual channel programmer will replace it.
The box underneath it a wiring centre for your Central Heating :)
Your programmer is going to be pushing 30 years old, so it can't hurt to change it :)
Depending on the design of the system it can be setup to run water and heating independent...
The fans very a simple motor. There's not much to blow there. They burn out if they seize, all this power flowing through the coil attempting to turn the shaft, it'll cook itself.
Could be the wiring harness, could be a issue with the PCB that drives the fan, could be a issue with the supply...
You need to find out what the static head is. The height the loft tank is mounted at determins your Hot water pressure.
You could also have a cylinder full of scale, you might find its blocking the cold inlet to your cylinder :)