Thoughts on pipes for new CH system

[SilverShadow]

Hey folks

 

I'm sure this question gets asked 1000 times, so apologies in advance if it has......

 

We're looking to replace our CH system in the next year (install a new combi-boiler, to replace the old gravity-fed boiler that seems to come from the steam-locomotive age! 🤪). This will likely involve moving the boiler location & hence alter the pipe layout

 

As part of this, i was originally planning to replace all the existing copper pipes. However, an old skool plumber mate of mine said it was just waste/way for plumber to maximise profits. Tbh, it's not as though copper 'wears out', but i'd imagine it'll be clogged with sludge

 

• Is he correct on his assumption it's ok to reuse the pipes?
• If we kept the old pipes, i presume they'll need flushing out thoroughly?
• A newer combi-boiler CH uses a higher pressure, so i wasn't sure if the old joints (soldered i'd presume) would stand up to this? (I'd bet the old gravity system is at least 30+ years old)

 

Any thoughts or ideas on this most gratefully received 👍

Shadow

 

[JohnMo]

I would get a full power flush before you start and assess.

 

Do you have system boiler now?

Or is another combi?

[Nickfromwales]

2 hours ago, SilverShadow said:

old gravity-fed boiler that seems to come from the steam-locomotive age!

👆. 
 

 

At 30+ years of age I’d replace any of the pipework that’s not 15mm or 22mm. “Microbore” needs cutting out if there’s any 8 or 10mm stuff in there.

 

Keeping the backbone and any ‘embedded’ runs is fine, just needs to be flush properly, eg thoroughly, and then a good quality magnetic filter installed to stop any nasty residual crud getting into the new boiler.

 

I’ve done these exact conversions so many times over the last 30 years that I must be in triple digits, so nothing to worry about at all, but the caveat is that you must accept that any pressure related failures will be on your head and not the plumbers; he’ll be connecting to pipework YOU own  

 

I’d say > 95% of the conversions done gave us no troubles whatsoever retaining at least some or indeed all of the existing pipe work (except the gas run which will defo need an upgrade). 

[SilverShadow]

4 hours ago, JohnMo said:

I would get a full power flush before you start and assess.

 

Do you have system boiler now?

Or is another combi?

 

 

I'd assume it's a system one, as it has cylinder & expansion tank

[SilverShadow]

Thanks NfW - very useful.

 

Yeah, i'd thought reusing the pipes might be feasible (with a lot of cleaning out!). From what i can see, none of pipework is microbore (at least, the pipes connecting the rads aren't!)

 

I wasn't sure how 30-40 year old soldered joints would stand up to the rigmarole of being yanked and dragged about when reconnecting/relaying the new pipework. Given that (afaik) combi systems are higher pressure than old gravity-fed, i just wondered about any minor leaks as a result. Realise there's never any guarantees anyway, but i'd assumed soldered joints would be just fine

 

[JohnMo]

18 minutes ago, SilverShadow said:

assume it's a system one, as it has cylinder & expansion tank

I would stay with a system boiler, but run unvented - you will have way better performance from DHW.

 

Get a good system boiler, that comes out the box equipped to run priority demand hot water, Atag, Intergas etc.

 

Read this article 

https://theintergasshop.co.uk/content/189-why-hot-water-priority-pdhw-is-the-reason-s-and-y-plan-should-be-banned

 

Get heat pump cylinder - NOT one sold for a gas boiler, you get a big coil for really quick reheat times. Then run the central heating on weather compensation or Opentherm, room compensation from a single thermostat ideally one from the same manufacturer as the boiler.

 

Video to watch also

https://youtu.be/_UQlGryL3JA?si=uRfZQWWvM6UMAhrE

 

Then sit back, knowing the boiler is running efficiently as it can do and is saving you around 30% in gas consumption.

[Nickfromwales]

Any solar PV going into the existing hot water immersion?

 

You’d lose that freebie if you jump to a combi. 
 

You’ll have to decide how much hot water you use, but there’s 2 adults and 4 kids (teens & upwards) here and I have a shitty Ariston combi I adopted and we have one bath & shower room plus utility, kitchen, cloak WC, and hot water is plenty survivable for us.

 

If heating a big tank of hot water all the time for just 2 adults then a combi will likely suffice, and newer combis are much better at she flow rates, just get a min 28-30kW size and you’ll be fine. 
 

If PV, go unvented & system boiler for the free summer hot water. 

[SilverShadow]

Thanks guys - the boiler is probably another topic in itself

 

For the record, it's a fairly small detached house (probably 8 or 9 radiators, once we've reconfig'd the house), 1 bathroom & only 2 of us here. The boiler's prime use would be heating a few hours a day, morning showers & the occasional bath. We don't have any solar, & a heat pump likely to be way too bulky/expensive for our needs.

 

Perhaps i'm wrong, but a full system boiler with tank feels a bit excessive & a combi would be the ideal solution?

 

 

 

 

Edited February 4 by SilverShadow

[JohnMo]

9 minutes ago, SilverShadow said:

The boiler's prime use would be heating a few hours a day, morning showers & the occasional bath

We are the same 2 off us, but find the house way more comfortable with a steady trickle of heat. You can keep the house cooler and feel way more comfortable, but also use the gas way more efficiently. So actual gas usage is the same or comes down.

 

Combi v cylinder, we have had both, we actually use less energy heating a modern cylinder than the combi did. The water out of the tap comes much quicker also from opening the tap. The combi would just fire up to full load of if you open a tap for a second or two. That doesn't happen with a cylinder.

[Nickfromwales]

Combi defo the right choice if you’re never intending to add solar. 
 

If only 2 of you then it’s a no brainer. 
 

6 minutes ago, JohnMo said:

Combi v cylinder, we have had both, we actually use less energy heating a modern cylinder than the combi did. The water out of the tap comes much quicker also from opening the tap. The combi would just fire up to full load of if you open a tap for a second or two. That doesn't happen with a cylinder.

The cost and disruption to the whole of house plumbing to retro fit an UVC here do not make sense vs the ‘slight’ uplift in gas use when opening a hot tap; bearing in mind you only ever do so WHEN you WANT hot water anyways?

 

There are just too many good combi’s out there, and if the remit is for lots of pockets of hot water through the day, hand / dish wash etc, then the likes of the Vaillant 938 (their heat store combi with 15L of stored hot water on tap) is the weapon of choice. Fitted loads of these and it’s as close to having a UVC as you’ll get without actually having one. 👌. 
 

Combi all the way here afaic. 👍

[SilverShadow]

Many thanks for the advice, guys

 

Sounds like a combi is the way to go. I've heard good things about Valiant, although read they use aluminium heat exchangers (apparently steel is best)

 

Something else we might take a look at, is a heat pump. Given there's a £7.5k UK grant, if we can get a decent one fitted for <£9k it might make sense. It'd have to be fitted in the garage though (which i've read conflicting reports as to whether it's viable)

[Nickfromwales]

4 hours ago, SilverShadow said:

Many thanks for the advice, guys

 

Sounds like a combi is the way to go. I've heard good things about Valiant, although read they use aluminium heat exchangers (apparently steel is best)

 

Something else we might take a look at, is a heat pump. Given there's a £7.5k UK grant, if we can get a decent one fitted for <£9k it might make sense. It'd have to be fitted in the garage though (which i've read conflicting reports as to whether it's viable)

It won’t be going in the garage!!! 
 

It would sap the heat energy out of the air in there in about 10 minutes. 
 

If someone says it can go in there then send them away 👉.

 

Vaillant HEx have never been an issue afaik, so I doubt that a real problem.

 

Many heat store combis out there so do a bit of googling. In honesty I haven’t bought a gas boiler to fit in over 6 years, so, unlike the aluminium, I’m a little rusty lol. 

[Nickfromwales]

1 hour ago, SilverShadow said:

Something else we might take a look at, is a heat pump.

You’ll need to install a hot water cylinder, plus it’s likely that you’ll need to change all the rads to much bigger, or have a high temp split ASHP, which would prob have much worse COP.

[SilverShadow]

Thanks Nick - we were looking to upgrade the rads as part of the refit (we've been looking at Milano Aruba, if you know them). Our existing system already has a cylinder, so that wouldn't be too much of a problem i guess

 

Essentially, when we change the CH it'll be not only a new heating system (eg: combi), but also new rads and a new location for the combi. We may opt for the combi in the loft (and a vertical vent through the roof tiles, as no gable end wall), but that's TBC

 

A heat pump was just something else to rule in/out. If it can't go in the garage, then it's a no-no, and if there isn't some variant (other than gas boiler) we could fit in there that's covered by a grant then it's combi as suggested above 👍

[JohnMo]

I would 

On 02/02/2025 at 16:23, JohnMo said:

I would stay with a system boiler, but run unvented - you will have way better performance from DHW.

 

Get a good system boiler, that comes out the box equipped to run priority demand hot water, Atag, Intergas etc.

 

Read this article 

https://theintergasshop.co.uk/content/189-why-hot-water-priority-pdhw-is-the-reason-s-and-y-plan-should-be-banned

 

Get heat pump cylinder - NOT one sold for a gas boiler, you get a big coil for really quick reheat times. Then run the central heating on weather compensation or Opentherm, room compensation from a single thermostat ideally one from the same manufacturer as the boiler.

 

Video to watch also

https://youtu.be/_UQlGryL3JA?si=uRfZQWWvM6UMAhrE

 

Then sit back, knowing the boiler is running efficiently as it can do and is saving you around 30% in gas consumption.

The above with you new lower temp radiators means your heat pump ready if you wanted at a later date.

 

Or a combi with inbuilt cylinder. But at a later date if you did change to heat pump, you need to replumb for cylinder.

[JohnMo]

For anyone scratching there head about gas boiler and heat pump cylinder, this is a plot of one. Note the boiler temperature, the dip at the end is the heat cycle going off 

 

 

Edited February 8 by JohnMo

[Nickfromwales]

2 hours ago, SilverShadow said:

Thanks Nick - we were looking to upgrade the rads as part of the refit (we've been looking at Milano Aruba, if you know them). Our existing system already has a cylinder, so that wouldn't be too much of a problem i guess

 

Essentially, when we change the CH it'll be not only a new heating system (eg: combi), but also new rads and a new location for the combi. We may opt for the combi in the loft (and a vertical vent through the roof tiles, as no gable end wall), but that's TBC

 

A heat pump was just something else to rule in/out. If it can't go in the garage, then it's a no-no, and if there isn't some variant (other than gas boiler) we could fit in there that's covered by a grant then it's combi as suggested above 👍

The only kick in the knackers with putting the combi in the attic is a much longer wait for hot water at the furthest outlet.
 

I’ve fitted scores of them in attics, but only after explaining this and the client accepting the compromise, so they don’t (can’t) come back and whinge afterwards.

 

Consider this as the combi (if not a heat store type) will need flow (open the hot tap) for a sequence to occur to light and get to temp and then you get premium temp hot water out.

 

A cloakroom basin hot tap a long way away wouldn’t see hot water in time for you to wash your mits after a pee, for eg. 

[SilverShadow]

Cheers Nick,

 

Only other thing we thought was whether some plumbers don't like going into the loft for servicing them?

 

As a rough guess, i'd imagine the taps would be 5-8m from the loft combi

[Nickfromwales]

44 minutes ago, SilverShadow said:

Cheers Nick,

 

Only other thing we thought was whether some plumbers don't like going into the loft for servicing them?

 

As a rough guess, i'd imagine the taps would be 5-8m from the loft combi

If there’s a combi in the attic, you have to do 3 things or a service agent won’t go up there:

1) there must be a fixed access ladder, not a steps. 
2) there must be lighting up there. 
3) there must be floorboards from the hatch to the boiler

 

5-8m isn’t too bad tbf, but best to know the pro’s & con’s   

[SilverShadow]

Thanks Nick - we've got an extendable loft ladder that you can pull down no probs. It's lit & with floor boards.

 

As a side question: do you know of any problems or no-no's with putting the combi vent through the roof tiles? 

Edited February 8 by SilverShadow

[Nickfromwales]

7 minutes ago, SilverShadow said:

Thanks Nick - we've got an extendable loft ladder that you can pull down no probs. It's lit & with floor boards.

 

As a side question: do you know of any problems or no-no's with putting the combi vent through the roof tiles? 

Happy days.

 

No problem at all, I've done more of these than I can remember.

 

The only thing you'll need (want) to do is chat through the clamping and screwing of the flue components, as I have seen a terrifying number of vertical flues where they've not mechanically fixed the entire flue system and you could literally just lift it off the boiler.

 

Also discuss all of the flue components being suitable, as there are horizontal flue and vertical flue options, and some parts cannot be used if it's a vertical; again I've seen loads of installs where we've then declared them as 'immediately dangerous' and have advised on getting it done properly (never goes down very well, but I am not the kind of person who would knowingly look the other way).

 

Ask questions, choose well, enjoy the benefits  

[SilverShadow]

Thanks Nick, good to know this up front 😁

 

I hesitate to ask more, but I have another general question, & your knowledge is golden:

 

For housing the combi boiler, does it always have to live on an outer wall, so the vent/flue go directly outside?

 

Realise in the loft this won't be the case if the flue goes out the roof, but wasn't sure if you could locate the boiler on any house wall & have a flue (eg 1-2m long) from it to the outside?

[Nickfromwales]

9 hours ago, SilverShadow said:

Thanks Nick, good to know this up front 😁

 

I hesitate to ask more, but I have another general question, & your knowledge is golden:

 

For housing the combi boiler, does it always have to live on an outer wall, so the vent/flue go directly outside?

 

Realise in the loft this won't be the case if the flue goes out the roof, but wasn't sure if you could locate the boiler on any house wall & have a flue (eg 1-2m long) from it to the outside?

It's all good.

 

You can fit the boiler pretty much anywhere, as these are mostly RS (room sealed) appliances which do not require "adventitious airflow" to function. The boiler sucks in fresh air to consume via the outer ring of the coaxial flue, and ejects the products of combustion via the inner one.

 

In attic installs nearly every one has had to go on a made up timber frame, and back in the day you could not mount the boiler on to a combustible surface; we clad the plywood frame with Ellis / cement board. Nowadays iirc there are plenty of boilers which no longer require this to be observed.

 

Rules with flues are, you must be able to see / inspect / 'get to' every mechanical joint. For a flue install where the flue was boxed in and tiled over at the ceiling level in a bathroom, I used a Vaillant boiler and their 4m flue extension, so as to not have any inaccessible joint. I asked the GSR agent to note this in the commissioning log, and to retain pics (same for client) for downstream evidence for future service / repair agents.

[SilverShadow]

Thanks Nick for all your help

 

Just thought i'd ask the last question, as it may be that space could potentially be an issue (if we located to somewhere that has a relatively small m2 outer wall area)

[SilverShadow]

As an aside and distraction, i followed up with the part on here mentioning heat-pumps......

 

We had a firm pop around to give us the spiel around this, just so i could have all the facts/costs to hand:

 

They were quoting circa £16k, for pump & installation (Vailiant, Mitsubishi, or Samsung - air source version). They also rightly (as mentioned on here) said they wouldn't put the pump in the garage, nor the side of the house (where the neighbours fence was <1m from our wall exterior) where we hoped it could live.

 

The did offer to install above the garaqe. However, as it's a sloping 'non-load bearing' roof then it'd need scaffolding, which would make the yearly servicing expensive/ impossible. It also seems like we'd need a servicing plan (circa £15/month), which i'd imagine pays for the yearly servicing up front.

 

They did offer to fit in another slot at the rear corner of the house. However, as we're potentially having a 2 story extension there next year, i was a little worried about damage/needing to remove it, in case any of the foundations/wall brickwork needing doing (as yet, we don't know). They were also a little sketchy about allowed rads with it (we were planning to use some Milano Aruba ones) - i guess they'd need to know if these are to spec as regards pressure/heat exchange, etc?

 

A heap pump feels like something we might do 1 day (with the £7.5k grant) in place, but maybe not with potential building work going where it's suggested location would be. They did mention the £7.5k grant would drop to £5k in April this year, but i couldn't find anything around that