What type of gas central heating, use?

If you are looking for a reliable boiler try something like Vaillant or Intergas.

Top 3:

1. Magic.

2. Good working and cost efective

3. working somehow...

To get more specific answer ask more specifically. Different cases need different solutions.

Now the question is whether you insisting to stay on a budget or not. Feroli, Heatline(now although wearing badges of: Glowworm/British Gas) Do not earn on boiler sales, but on replacement parts

I do not fit 24KW boilers because in colder winters they get problems supplying shower so I would start from 28. That can supply average terraced, two floors plus antique 2-3 rooms per floor house with plastic windows and insulated roof with up-to three floors If you do not have insulated roof DO it. Return on investment is less then a year...

if you don't have plastic windows do it. return may be up-to three years but health effect is massive...

I would recommend dependant on a Budget either new Baxi (around 750 pounds) and should if fitted correctly hold for next 10 years and after few patches another 10 or if you are Ok to invest you can go For vailant (1100 pounds) which except occasional fan replacement could happily hold 20,30 years

No point of fitting Worcester though all the "older" plumbers like them (They were the Best when they were young)...

repairs may come up-to to three times the cost of work (everything is hard to get to)

There is no point of keeping feroli running, you will spend in next two years more then a price of good boiler

Do not use British Gas boiler as you are going to spend loot of money for "Things that warent covered" plus will need frequent visits...

Cant understand what you are asking, be more specific. Do you mean mains gas or LPG?

Do you mean what type of boiler?