Worth swapping to an unvented cylinder? + other questions

[Skrufpipe]

Hi, I currently have an old boiler (regular) that is playing up, so I am looking to get it swapped out.

I have briefly talked to a plumber who thinks I might be able to get away with a larger combi, and as a whole, I agree, but I suspect this situation will change.

Bedrooms: 5
Radiators: 17
Bathrooms/Showers: 3 (all showers are currently electric)
Bath: 1
People: 2/3 adults, 2/3 kids (a parent visits for months and one kid is only here at weekends)

At some point in the future (within a couple of years) I would like to swap out at least one, but perhaps two of the showers to run from the hot water supply. The kids are still young enough that we are supervising them while they wash, so only use the bath/shower one at a time, but I suspect there are only a couple more years of this.

The combi boilers that I have been looking at have been the Viessmann 200-W 32kW and the Worcester Bosch Greenstart 8000 50kW. These 2 in particular claim to have flow rates of 17l/m and 18l/m respectively. Are these numbers accurate? (I tend to be sceptical about marketing literature) and would you realistically be able to run 2 showers from it comfortably?

The current system uses a vented cylinder, but I have done a fair bit of reading on the unvented (indirect) cylinders and their ability to provide mains pressure hot water for the showers, and I wouldn't be limited to the low flow rates of the combi. These appear to cost more than £1200 for anything of a decent size, which when coupled with a new boiler becomes fairly pricey. Is it going to be worth the expense to fit the unvented system? How much hassle/expense is it to replace the vented system with this?

My main interest in the Viessmann is the modulation and the reported quality. Assuming I go with this brand, do you need to have a Viessmann trained installer to get the warranty (7 years)? I have checked for local installers, but there are not many around my area, and getting any plumber can be difficult at the minute, so narrowing it down to a subset is not likely to help me find anyone.

Open to other ideas and suggestions on this system.

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[Mottie]

I have done a fair bit of reading on the unvented (indirect) cylinders and their ability to provide mains pressure hot water for the showers, and I wouldn't be limited to the low flow rates of the combi.

As far as I know, with either combi or unvented, you would be limited by the incoming pressure/flow of your cold water supply.

 

[Madrab]

Bedrooms: 5
Radiators: 17
Bathrooms/Showers: 3 (all showers are currently electric)
Bath: 1
People: 2/3 adults, 2/3 kids (a parent visits for months and one kid is only here at weekends

Never, Never, Never a normal combi in that size of house without a serious rethink of outlet design and close management of water usage + times. Possibly a storage combi (111-W) but even then that would struggle once all the storage had been used up. If the mains can support it then an unvented cylinder and quite a good sized one too, at least 250L would be my starting point with either a regular or system boiler. Most reasonable boiler will modulate

Claimed output for the combi are accurate, they have to be otherwise they would be hung draw and quartered but there would be some poetic licence and would really be dictated but mains, environment, pipework etc

1st thing to do is have your mains water supply surveyed and see what the dynamic delivery can be. Then take it from there.

Unvented systems can be pricey but depends on what systems you opt for, the unvented cylinder can be a direct replacement for the vented cylinder as far a location is concerned, it can use the same distribution pipework subject to a survey and the mains can be dropped via the same cold water pipework that feeds the cylinder at the moment, mains supply to the cistern in the loft dependent.

I believe the Viesmann 7Yr is through the homeowner portal so an accredited installer wouldn't be required.

Viessmann product warranties | Viessmann UK

See a full list of our products' warranty prices and register your Viessmann products to make sure your product is protected. Read more

www.viessmann.co.uk

 

[Skrufpipe]

Thanks @Madrab.

Water pressure in the area is generally really good, so I wouldn't expect any issues there.

With regards to unvented cylinders, what are the main points beyond looking at capacity, flow rate and reheat time?

I have not done a lot of research on these, but I see that Megaflo Eco Plus 250L is coming in around £1850(PlumbNation), but others seem to be around £800-£1200, which is quite a difference. I also noticed that the MegaFlo Eco Play 250L in direct heating mode is £200 less than the indirect version, why would that be?

 

[Madrab]

Water pressure in the area is generally really good, so I wouldn't expect any issues there.

It's not about expecting issues @Skrufpipe, to run an unvented cylinder especially a good sized one with the number of bathrooms and other outlets you may have, there is a min dynamic flow and pressure you want to have available. That would be >20L/min @ 3 bar dynamic, so it's really important to know exactly what the mains can deliver.

I would stay away from Megaflop's, they have a great name but overpriced. OSO Super coils are a good cylinder, they're Powercycls are top drawer, Telford's tempest range are good too, Gledhill's Plus cylinders are good too but it's all about recovery times, price point, availability etc you really want a good experienced installer in to survey and have a good chat with you to understand what you actually want from the system

Direct cylinders use immersion elements to heat the water, indirect use internal multi heating coils with fast recovery, so would be more expensive to manufacture

 

[Skrufpipe]

Thanks again @Madrab

I had not come across OSO before since they don't seem to be listed on the sites that I have been looking at. Would I be correct in saying that the recovery time on the 250L model is 34 mins? https://osohotwater.co.uk/product/super-coil-hot-water-cylinder/

About experienced installers, how do you tell? I briefly know a couple of plumbers and know they do good work based on the work that I have had them do, and the reviews of others (not that this should hold any weight), but this has always been with combi boiler installation and repairs (they are reputable installers/companies that have been around a long time). Given that I don't know my earhole from my... on this kind of install, what should I be looking out for?

Concerning the boiler, do you have any recommendations? The modulation ratio of the Viessmann is what drew me to them, I tend to have someone in the house 24/7, and with that, I am heating the house constantly in the darker months and I am assuming the lower modulation ratios of the Viessmann should be more economical over the course. I know everyone recommends what they know well, but I would be hoping for an unbiased view on this one. I had an Ideal Vogue installed in a previous property that was fantastic until it wasn't (it was faulty from the get go, and the installer didn't seem to see that even though was his preferred boiler type)

And hopefully the last question (maybe), what should I be budgeting for this installation? ballpark of course. I had originally thought 3K for a straight boiler swap, but with what now looks like a boiler and a cylinder, it has a 5K feel about it. I was originally hoping to have one of the showers replaced as part of the installation, but like everyone else, there is a limit to my resources.

 

[Madrab]

Would I be correct in saying that the recovery time on the 250L model is 34 mins

Yes - that's considering a 70% requirement to reach full temp

About experienced installers, how do you tell?

That's the million dollar question isn't it. Recommendations - Experience - checkable reviews, previous works and credentials - everything in writing - constructive discussions and planning - gut feeling - etc

Concerning the boiler, do you have any recommendations

Another million dollar question, if modulation is the key then a good boiler coupled with good controls is important - Open Therm/weather compensation is recommended to optimise efficiency. Viessmann are good boilers, as are Vaillant though most modern boilers modulate these days, it's all down to ratios
Intergas have great boilers (my favourite) and they can modulate a little lower than Viessmann/Vaillant. Some have longer warranties if their filters are used. It can be quite specific and again that would be borne out of discussions and requirements.

what should I be budgeting for this installation

Honestly, IMO that's not a question that can really be answered over the net, there are far too many variables that can alter a price quite significantly when it comes to specific sites, levels of hardware, where in the country you are etc