Sometimes, it can be really aggravating that the boiler seems to be functioning properly, but you get some particular radiators that never seem to heat up or take ages to get hot. Other potential issues could be at fault here. Some of the more common reasons for this type of issue include air trapped within the radiators, the presence of sludge, unbalanced radiators or a faulty valve. It may also not be the boiler itself that's the problem here – you could be facing issues with water circulation in the system, rather than the boiler itself. If you look online about a boiler repair Bristol, you're sure to find other people that have experienced this kind of issue. But, what causes this kind of problem?