In my continuing efforts to spend any spare cash I have (sobs) we’re getting quotes to get a new combi boiler and bigger rads to replace a c.20 year old conventional boiler and rubbish single panel radiators in a 3 bed house.

Question is: is it likely to be false economy to *not* have pipework replaced too? The existing system is (layman here) gravity fed apparently and the new one will be sealed (??) and I gather that this will mean higher pressures in the pipes.

Is this another impossible question or is there a sensible (and easy) rule to go by? Cheers in advance as always.

The pressure will not be an issue, however increasing the heating load on the pipework may well be an issue and some of the pipework be undersized. You can put the biggest rads in you like but if the pipework can’t carry the volume of water required to make them perfrom then you are wasting money on the rads.

I’m not saying that you need to do it, but you need someone to perform a heat loss calculation and a pipe size table to prove the sizes. Some plumbers will be able to do this for you, not many will want to though, but poor system design is inexcusable in my opinion. And this is where the cost of estimates can be a real pain, someone using mainly 15mm and a bit of 22mm will be a lot cheaper than someone who is using 28mm, some 22mm and some 15mm. choose wisely!

We had it done recently.

3450 using old rads, one new one in the lounge, one in the bedroom cupboard and a towel rail.

20mm pipe all round replacing the microbore that was there before. The owner was thinking about not doing it, but the quote ended up being only 800 quid more, so he went for it. Copper piping as well. House heats up fast and there is no risk of the pressurised system popping the microbore in the walls.

Interesting, thanks…

Bloomin’ minefield innit. My dad (a plumber by trade for 30+ years) will be turning in his grave at my ineptitude 😉

change pipe work has you will prob get leaks fittings may go under pressure it wont cost that much extra and at least you no it will last 30 years

15mm and a bit of 22mm will be a lot cheaper than someone who is using 28mm, some 22mm and some 15mm. choose wisely!

Do you not also have an issue with turbulance (?) when dropping sizes?

Check the bore of pipe for gas and water into the boiler.. as mentioned, undersized pipe will reduce efficiency…

What Bear said. And use copper, not plastic. Fit a Magnaclean or the something similar too.

We survived not updating the pipes or radiator when going to a pressurized system

I would recommend you replace the pipework as if its that old it will may be gunked up in places.

Also putting ‘mains’ pressure on old pipework could give you a leak seen it happen (although if its old copper less likely).

Also go copper as plastic pipe expands a lot and I’ve seen the pipe pull out of elbows (plus it just looks plain mingin).

Changing from old skool to condensing and should operate on a 20 degree delta T so pipes will be small. Gas one may not be though…

Also a complete system means that if anything does go wrong the plumber can’t blame old pipes, etc.

HTH.

Question is how much more will it cost to insert the new piping? How many run into/inside the walls and under which/how many floorboards?

Also listen to the quotes from 3 plumbers- what each of them recommends doing.

The gunk tends to live inside the radiators and a overnight cleaner left in the system then inhibtor will sort out.

30yrs? Who lives in their house for 30yrs these days? 5yrs more like.

Listen to each plumber- then make your decision.

Ps. We’ve recently had new combi and all boilers

Ja, had three plumbers round.

– First one said he could test whether the pipes would hold the pressure by pressurising and seeing if it held(????)
– Second one didn’t really mention about changing pipes, although haven’t got the quote yet so can’t say what he’s including
– Third one pretty much said he would recommend replacing pipework but would quote for not as well

Not had any of the quotes yet, mind, but can imagine they will cause a sharp intake of breath whichever way 🙂

pressure should not cause a problem as you will not be raising it a huge amount. More likely to get problems from all the valves etc. Some plastic systems are good, I prefer a crimped system which over the last 7 years has proved very reliable. fittings bit expensive, pipe ok, but leak wise it is the most reliable system I’ve used, including copper as had far too many pin holes / mis soldered fittings.

15mm if ran correctly is plenty big enough for a 3 bed house, main problem is usually size of gas supply to the boiler!

Doing a house extension at the moment, and in the process i’m removing all the 10mm microbore in the older parts of the house and replacing it with the 15mm plastic stuff.

Reason I went for the plastic is that i’m running single lengths of pipes from the manifold tree all the way up to the rads themselves. No joins in the run of pipe. That way if there is a leak, its going to be at the radiator ( where its accessible ), or the manifold ( where it’ll be accessible under a hatch under a carpet, rather than having joins under sections of the house where the floor cant be lifted ( I’m putting it a fair amount of tile / stone flooring )

Wrightson – another magnificent generalisation that is based on what exactly?

As a rough idea how many watts can 15mm carry please?

15mm x 15mm =30mm to a rad is plenty any bigger and will run s**t

why will it run shit? I’m interested to know why, and if the rad is 40m away and is 3kW and the run has 20 elbows, can you then guarantee that it will work?

Stop generalising please.

Generalising in the fact that generally most 3 bed houses generally will run fine on a system generally run with nothing generally more than 15mm!

Oh and a bit of 22mm from and to the boiler, generally!

I put in a new combi & rads, about 5yrs ago. I kept the exisitng (est)20yr old, 15mm piping. Added cleaning solution, then flushed it through off the mains. If the pipework is 15mm, & good quality, I’d not go ripping it out.
They typically run at about 1.5 bar, not mains water pressure surely. Mine doesnt.
Hardest job was routing 22mm to the airing cupboard.
Whatever you do, try & get them to route the condensate drain to an internal waste pipe, save it freezing up over the winter.