Should i replace old copper pipes?

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Hi team,

I'm going through a whole house renovation, and just about to start on the ground floor. Oil boiler already replaced with a system boiler and heat exchanger as installers didn't want to trust the old pipe work to withstand pressure.

I've now worked out rad sizes and pipe sizes for running house at 50 degrees and so am working my way round replacing bits 1 room at a time. The old copper is still very thick and all on compression joints.

My main q is whether i replace the main branch downstairs which is 35mm with new 28mm, or whether I should just pressure test it and check for leaks? Would replacing it really ensure longer life, or do you think the older thicker copper and quality fittings should last?

Ideally looking for a heat pump in the future, hence the leg work now and possible need for pressure at some stage.

Thanks all very much (and sorry about the pic, it was more to show my underfloor insulation should EPC ask in the future!)
IMG_20220520_100632.jpg
 
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i would pressure test without a doubt, if you do find a leak on a comp. fitting it can be dismantled and re made with some jointing paste. Love that old stuff gotta be literally 2x. thicker than new. ( imperial sizes of course)
 
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i would pressure test without a doubt, if you do find a leak on a comp. fitting it can be dismantled and re made with some jointing paste. Love that old stuff gotta be literally 2x. thicker than new. ( imperial sizes of course)
Thanks Nige, do you have experience of dismantling and putting back together? I thought about doing that to one of the 35mm joins, just to make sure that section is clean and tidy but was worried about it not tightening up well again. A bit compound would help as you say.
 
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God I must be more hungover than I thought.... looking at that picture I thought it was a wall for a few seconds!!
 
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If it was mine, I'd change it.

If you're completely renovating then there's a good argument for changing out the old copper. If any of those joints, especially where there are 'adapters' converting old imperial sizes to current metric, decide to weep after the floors are relaid then you'll be weeping too.

The old felt insulation needs repair/replacement so that's another reason added to the argument

The old copper, removed of all brass fittings will probably pay for the new when you turn it in for scrap. Copper with brass attached will only get you brass scrap value., scrappy's gain, your loss.
 
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If it was mine, I'd change it.

If you're completely renovating then there's a good argument for changing out the old copper. If any of those joints, especially where there are 'adapters' converting old imperial sizes to current metric, decide to weep after the floors are relaid then you'll be weeping too.

The old felt insulation needs repair/replacement so that's another reason added to the argument

The old copper, removed of all brass fittings will probably pay for the new when you turn it in for scrap. Copper with brass attached will only get you brass scrap value., scrappy's gain, your loss.
That's where I think you might be wrong - I've priced up replacing in both 28 and 35 and it's pretty costly! I think I probably should just replace them, even though logic tells me otherwise. I can't see how an old compression fitting will be any worse than a new one, and new compression fittings do well over 50 bar. Peace of mind tho...
 
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That's where I think you might be wrong - I've priced up replacing in both 28 and 35 and it's pretty costly! I think I probably should just replace them, even though logic tells me otherwise. I can't see how an old compression fitting will be any worse than a new one, and new compression fittings do well over 50 bar. Peace of mind tho...


Then why ask the question.
 
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Why 28 and 35mm heating pipe for what is a pumped system - is it a mansion you're working on ?. Most domestic pumped systems are plumbed in a mix of 22 and 15
 
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Why 28 and 35mm heating pipe for what is a pumped system - is it a mansion you're working on ?. Most domestic pumped systems are plumbed in a mix of 22 and 15
Yip, pretty much! Needs 25kw of heat, so 3 times the norm!
 
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If only 25kW then your piping at 35mm seems way oversized. I'm running up to 36kW on 22mm quite happily. Yes, your water will flow very quietly but a waste of boiler fuel, heating up a bulk of slow flowing water and a waste of money buying oversized copper. In comparative numbers 22 = 8/m 28 = 11/m 35 = 18/m So it seems you'd be paying between 2 and 3 times the price for an overly 'engineered' system
 
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How big is your new boiler and the house?
It's a 46kw vaillant - certainly oversized. The house is 300sqm Victorian. I'm going room by room, insulating as I go. Once I'm done I'll need 18kw of heating, assuming I can insulate as much as I hope. I've also calculated correct size rad for each room based on heat requirements, and then what sized pipe assuming 50 degrees flow. 28mm is just big enough at 0.9m/s flow, but no harm in being bigger. Was wondering more about the quality of old fittings - I couldn't solder 28mm confidently, and don't have 28mm pipe bender, so if old fittings are as good as new, I'd just leave them. Tricky call, but gut says replace while wallet says keep :)
 
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If only 25kW then your piping at 35mm seems way oversized. I'm running up to 36kW on 22mm quite happily. Yes, your water will flow very quietly but a waste of boiler fuel, heating up a bulk of slow flowing water and a waste of money buying oversized copper. In comparative numbers 22 = 8/m 28 = 11/m 35 = 18/m So it seems you'd be paying between 2 and 3 times the price for an overly 'engineered' system
The 35mm is actually inch and a quarter and is already there, so it's more a question if it's worth replacing. More volume would suit a heat pump down the road, and running at 50 degrees, you need bigger pipes than running at 70. So I'll need 28mm based on calcs. The actual boiler is 46kw which modulates down to 6 and has weather comp.
 

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