i have a main meadway water heater. The hot water pressure on all my taps is too low to fire up my water heater????

know this sounds silly but have you tried seeing if you can open your mains stopcock anymore. if not then you may have old lead pipe which means renewing it to polypipe.

sounds like it could be a blockage within the mains feed to the boiler or a filter clogged up within the boiler, there are several reasons why this is but these are the two i would investigate first. Bob Gemini Plumbing Services

incorrect pipe diameter can cause not enough flow and restriction

The reason you are having this issue is due to limescale build up behind the water switch. Unfortunately most medway are obsolete now so I advise a vokera easiheat it will require mains power and change from balanced flue, but is quite an easy job 👍