I've just bought a flat (1900s conversion). I having a new bathroom and combi/condensing boiler put in and wondered what the general consensus was on the central heating. Do I need to / should I replace the rads and flush the system if I'm going to put in a new boiler or will it be okay just to connect the new boiler to the existing system?
It should be properly flushed and cleaned before the boiler is installed or the warranty on the boiler may well be voided.
The same should be done, typically with a desludging cleaner after installation to neutralise fluxes etc.
If you identify the boiler, you should be able to find the installation instructions on the manufacturer's web site. That will give anything specific, but the above is normal good practice.
Domake sure that the installer does it.
A lot depends on the age, condition and adequacy of the existing radiators. With a new boiler, you will very likely end up with a non-vented (pressurised) system - whereas it may be vented at present. If the radiators are suspect - particularly if corroded - the higher pressure will probably finish them off, and you will have leaks all over the place. At very least, it's a good idea to replace the valves - and probably mandatory to fit TRVs on most radiators, if they don't already have them.
The other question is one of heating capacity. Are the existing rads the older, non-finned, variety? Do they produce adequate heat? If the heating needs a boost, replacing non-finned with finned of the same size increases the heat output by about 50% without taking up any more wall space.
Cheers guys, sounds like I need to have a proper look at the rads... and then rip them out and put new ones in. Haven't actually completed yet, I'm just trying to get on top of the issues so when the keys are mine I can get started straight away. It is a bit of a project so no doubt I'll be a frequent visitor to this site!
Well, there *some* truth buried in there somewhere - but you're mixing up two things.
A combi uses mains pressure for domestic hot water - but that doesn't go anywhere near the radiators.
Most combis use unvented (pressurised) systems - and thus run the heating circuit at a higher pressure than vented systems - but still not usually as high as mains pressure.
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