Without talking about makes of boiler there are a number of options.
A while ago we were all going for comb boilers but with the move to solar power there has been a move back to storage tanks so first question is are you likely at any time in future to use solar power?
With storage tanks we have open and closed vented and also pressurised coil and pressurised tank I know there is an issue with pressurised tank in that it needs an annual test. From what I am told much depends on hardness of water as to which system.
The new boilers are more efficient than the old boilers but that has also resulted in some problems. Now both the feed and return temperatures are monitored so all radiators must have radiator thermostatic valves and the lock shield valves need careful setting. The boilers have a lot of electronics and in some cases this includes anti-cycle software and for this to work ALL radiators need thermostatic valves. What it does if the water is returned hot within a set time it tells software to increase time between testing if radiators valves are open or closed. Conversely decreases time if it takes a long time to return hot.
In theroy as a result there is no need for a room thermostat. However placing a thermostat where it gets the morning sun can stop central heating firing up on what promises to be a nice day. Also it stops the cycling in the summer.
There are also now boilers with built in Sterling Engine generators which feed back into the grid with a grid tie inverter in the same way as solar panels getting even more energy out of the gas than the standard condensating boilers.
As to which make you need to ask in plumbing section but first you need to work out what system you are going for.
One of the problems is even firms which fit boilers every day don't seem to be keeping up with the changes. My parents had a new combi condensating boiler fitted and the fitters left three radiators without thermostatic radiator valves (Two were towel rails) and a wireless thermostat in the hall where there was no thermostatic valve on the radiator as would have been done with the old type boilers. they also completely missed noticing that there was a power shower fitted and these will not work from a combi boiler. (In fact it's illegal) This firm fits central heating every day using a team of fitters so it seems going to the large firms is not always the way to ensure it's done right.
They also failed to adjust any of the lock shield valves. So re-heat times were very long.
As to what questions to ask to find out if the guys know there trade or not I don't know. Clearly they were gas-safe but also clearly form what happened to my parents that does not make them good installers.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!