Do I need new radiators?

[JavaEnquirer]

I'm upgrading my boiler to a condensing combi. The radiators and pipework were installed about 20 years ago. I don't know much about plumbing and I'm getting competing recommendatiosn from the plumbers I've called in. All but one have said that I should replace my radiators because even after flushing there's a risk that "muck" from the system could damage the boiler. One said that this was nonsense and that I need only replace the radiator valves because they don't look as if they can take the pressure the new bioler is going to deliver.

Any advice? Many thanks in advance.

[Stuart]

On similar lines someone on here suggested that if I was replacing my boiler that I should get the microbore system ( I would be renewing the rads) flushed out ....not powerflushed tho'

Stuart

[manatbandq]

See the "Neighbour's ch" thread

MBQ

[John Rumm]

If your rads have been looked after (i.e. inhibitor has been used in the system in the past), then there is no reason they should need replacement at that age. The chap who suggested that the valves may not be up to it however may have been right, so you could swap them all out first, or pressurise it first and see what happens. If you need to add Thermostatic Radiator Valves (TRV) to lots of rads then you may as well do the lockshield valves at the same time to save potential hassle later. Note that when I converted my system of a similar age from vented to sealed all of the lockshield valves survived without any problemm so I just added TRVs to a couple of rads that needed them.

If the rads are on their last legs then conveting to a pressurised system probably will advance the onset of their demise, but it won't do anything that would not have happened soon anyway.

As to "muck" in the system, one ought to add a flushing agent to the existing system a couple of weeks before decomissioning. Then flush it well when the new system is installed, and treat with inhibitor. A strainer should also be fitted to the return on the boiler to catch any debris before it gets into the boiler. However if you have done the first bits correctly, there ought not be much if any debris to get to the boiler in the first place. (subsequent inspections of the strainer on my system revealed one singlular grain of rust or debris and nothing else in the following two years!)

[Roger Mills]

If the radiators are in good condition, there's no need to renew then. But they'll have to be disconnected in order to change the valves, so the opportunity should be taken to take them outside and give them a really good wash out with a hose pipe.

For a condensing boiler to work at its maximum efficiency, the water temperature needs to be lower than at present - which reduces the capacity of the radiators. For this reason alone, you may wish to replace some or all of the radiators for larger capacity ones. Replacing non-finned with finned of the same physical size increases the heat output by about 50% - which would compensate for the lower water temperature.

However, it would be advisible to do a heat-loss calculation for the whole house, plus a sanity check on radiator capacities. It may well be that the standard of insulation - loft insulation, cavity wall insulation, double glazing - has been improved since the heating system was installed, so the existing radiators may have some spare capacity relative to the current losses.