My gas central heating system seems to have stopped working, it started to make a loud humming noise....?

Hmm I'm gas engineer, it could be the pump or chip it's hard to tel off a description. If it's bangning it could also mean the flu isn't conected properly but that is only on newer boilers. A pump change isn't to much in the uk for labour an part maybe 100� maybe lil less . It's hard to discuss on here, u can get good standrrd boilers baxis for 600� so keep that in mind if u start needing to get a few differant repairs . Heating systems are expensive :/