Secondary Heat exchanger Replacement and draining system?

I have to replace the secondary heat exchanger again in My heatline S30 boiler again!!. Does anybody know if I need to drain the system down or do I just need to turn off the water supply. It would seem to me that the the divertor valves mean I should get away with just turning off the mains water, or am I missing something Thanks in advance
Steve
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On Feb 28, 12:40 pm, snipped-for-privacy@scannex.co.uk wrote:

Hi, when I remove mine (an Ariston) I need to turn off the incoming mains water (which goes through the secondary water circuit) and also isolate the flow and return through the primary circuit, which is just a matter of a quarter turn of the relevant valves going into the boiler. Incidentally, before I do isolate flow and return I drain a couple of pints of water from the system so that it's not under pressure, otherwise you'll get a sudden burst of water when you remove the exchanger.
Do you really need to replace it? Unless it's leaking or damaged in some way you can usually restore it to full functionality by descaling and generally flushing the crap out.
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wrote:

Thanks, Have descaled it a couple of times now, had it 9 years, and wondered if its time to replace this time? Does anybody think its worth trying and clean the rads out by flushing the system with fresh water, as power flush seems very expensive! Thanks
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     snipped-for-privacy@scannex.co.uk writes:

It's expected to scale up from time to time in hard water area. It's not generally expected to fail. If the primary side becomes blocked with rust flaking away from the insides of the radiators, that can be hard to clear out. Hard water scale on the secondary side should be easy, but don't underestimate the ammount a heat exchanger can hold, and you will need a lot of descaling chemical. I'd suggest buying a tub of Furnox DS-3, which is designed for this. It's Sulphamic acid, combined with an indicator dye so you can tell when the solution is used up and needs replacing, and a perfume so you don't accidently drink it.

Only if you have some reason to believe it needs doing. A properly maintained system shouldn't corrode and leave debris in the radiators. If radiators are cold at mid-bottom and both pipes are hot, then that indicates a pile of sludge in the radiator.
--
Andrew Gabriel
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On Feb 28, 4:33 pm, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

I have noticed radiators at the top of the house which are a cheap variety when bleed produce blackish water and on one double panel rad the rear panel does not heat and if bled produces nothing, air or water, though as far as I remember its always been cold on rear panel The downstairs expensive Delonghi ones produce nice clear water, not sure if that helps. Thanks for your advice.
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