Combi boiler using old central heating flow and return

[Rodders]

Hi all,

Just a quick question that I have so far received mixed views on.

I currently have a vented central heating system, which I plan to have replaced with a combi boiler in the garage. In order to link up with the existing network, one plumber suggested sending the cold water from the airing cupboard (that currently houses the tank) down one of the pipes that feeds the coil in the tank, and likewise sending the hot water up the other.

This sounds fine and makes sense to reuse the existing network, but another plumber said it was not possible due to the chemicals used in the central heating system, and you shouldn't run fresh water down it (this will not feed the kitchen tap, which is taken directly from the mains).

Could someone please clarify whether this is true. I guess pipes can be flushed or sludge etc, but would any chemicals linger in the pipes that may make it unsuitable for showering, washing hands etc (everything but drinking)?

Thank you for your help
Chris

 

[ShaunCorbs]

the second plumber is correct but technically you can do it but you need to flush and clean the pipework and then sterilise and make safe

but tbh i wouldnt trust the first plumber to do this

 

[Rodders]

Thank you for your comments.

Can I please check why you wouldn't trust him to do this - is it not good practice? The pipes are approx. 10 years old if that makes a difference.

Thanks
Chris

 

[ShaunCorbs]

well if he hasnt told you they need cleaning in the first place its unlikely hes going to do it

 

[Rodders]

Thanks Shaun, appreciate your comments

So the bottom line is it can be done...if done properly!!

 

[ShaunCorbs]

Thanks Shaun, appreciate your comments

So the bottom line is it can be done...if done properly!!

yes

 

[Chalked]

I’ve done it before.
Apart from cleaning and flushing the pipework. There is more draw off time , as the pipes are larger than would be fitted from a combi.

As long as you know the pitfalls, it’s ok.

 

[Rodders]

As in the volume of water you'd need to run through the tap to clear the cold water is more with a 25mm than a 15mm, ,therefore you're waiting around for longer for the water to run hot. I didn't really think of that - just assumed bigger was better!

The longest run from the boiler would be c.12m - so a bit of old school maths suggest there should be around 6 litres of water in a 25mm pipe compared to 2 litres in a 15mm pipe. I've got around 20 l/m of waterflow, so basically it will run cold for 20 seconds, plus a bit of boiler fire up time etc.?

 

[Harvest Fields]

Thanks Shaun, appreciate your comments

So the bottom line is it can be done...if done properly!!

Even though I agree with what has been said above. I still wouldn’t recommend it. Why spend that much money on a new boiler and then cut corners on this. Just run a new section of pipe. You will be much better off in the long run.

 

[Rob Foster]

putting boilers in the garage is also not always good I did because it was easier and safer BUT when it gets cold you may have to run heating just to protect boiler or fit frost stat and with the price of gas I would not do it again. My BIG hate is boilers in bedrooms noise and ultimately unsafe practice IMHO

 

[Rodders]

Thanks again for all your comments.

I'd happily rerun the pipes, only it would either require ripping up the bathroom floor, or going from the underside through the lounge ceiling. It's more balancing the destruction, but totally agree that if doing it, do it properly.

Is there any reason I couldn't thread a 15mm plastic pipe through the 25mm copper - its a completely straight run? Stops the squirrels too!

Thanks
Chris

 

[Last Plumber]

Thanks again for all your comments.

I'd happily rerun the pipes, only it would either require ripping up the bathroom floor, or going from the underside through the lounge ceiling. It's more balancing the destruction, but totally agree that if doing it, do it properly.

Is there any reason I couldn't thread a 15mm plastic pipe through the 25mm copper - its a completely straight run? Stops the squirrels too!

Thanks
Chris

I would do the job properly or not at all.

You need to run the right size of clean copper or plastic pipe from A-B in my opinion.

The circs in there at the moment from the old Cylinder will more than likely be 22mm or 28mm O.D. They are too big for this job as has already been said plus they will be filthy.

Not only is there a risk in ingesting contaminated water for members of your household, there is a risk of contaminating the drinking water main, which is against water authority regulations and bylaws and puts other people at risk of ingesting contaminated water too.

There is also a chance of washing whatever nasty particles are in there through into your plate heat exchanger in your new Boiler.

Please have it done properly. Anything else is wrong. In my opinion.

 

[Rodders]

I think we're all in agreement that I shouldn't be using the old copper pipe - whether it's chemically sterilised or not.

I was wondering now whether I could thread a new 15mm plastic pipe through the old copper - simply using it as a sheath, as no water will be passed through it? Hopefully it should just push through as it's about a straight run.

Thanks

 

[Harvest Fields]

I think we're all in agreement that I shouldn't be using the old copper pipe - whether it's chemically sterilised or not.

I was wondering now whether I could thread a new 15mm plastic pipe through the old copper - simply using it as a sheath, as no water will be passed through it? Hopefully it should just push through as it's about a straight run.

Thanks

But the new pipe will scrape all the way down and through it. Honestly, just take the floor up. You will Thank us all in the long run.

 

[AWheating]

Against water regs, bacteria and contamination issues. I wouldn't want to drink or shower in my central heating water MN