Which Boiler?

[lumi]

We are moving houses next week and need to get a new heating system pretty promptly. However the two plumbers we've seen have given different advice and we don't really want to get this wrong.

The house has 2.5 bar pressure from mains. The house has 5 beds, 2 bath, WC, kitchen, utility room. We don't share the pipe off the mains with anyone else. The heating sytem is very old and absolutely everything needs replacing.

Although we have space for a traditional system we've been told that no-one installs those anymore.

One plumber has suggested that a Highflow 440 is the way forward as it has an integrated tank. However a friend has this sytem nearby and although their shower is good, filling the bath is quite slow.

The other suggests putting 3 tanks in the loft and pumping these to a 42kw combi boiler. The first suggests that this system is likely to have problems as the tanks in the attic can't be sealed properly and getting dirt into the boiler will destroy it.

Are there other alternatives we should consider?

We don't have loads of time to decide and are afraid that we will seriously regret it if we get the decision wrong!

 

[gas4you]

Firstly there are loads of traditional systems still installed today. Sounds like whoever told you this only wants to fit a combi

With 2 baths you should in a perfect world look to fit a system boiler, probably around the 24Kw size for your property and an unvented hot water cylinder.

I would recommend the Vaillant Ecotec Plus 624 with the Vaillant Unistor 210 linked with a VR65 centre and a VRT360F programmable room stat.

Normal combi's will only efficiently supply one hot outlet at a time.

If you really want to go the combi route then the Highflow 440 is good, but for better water flow that lasts longer go for the Vaillant Ecotec Plus 937. Nothing compares to it and it is the latest technology out there at present.

But go the non-combi route if you can and don't be fobbed off by the installer quoting the job.

 

[Doctor Drivel]

Forget tanks in the loft. Look at the simpler combi route first.

High flow models are available:

Wall mounted:
Alpha CD 50
Glow Worm Extramax
Vaillant 937

Floor mounted:
Viessmann 333
Worcester Bosch 440 Highflow
Vokera
ACV HeatMaster
Atmos Multi
Gledhill Gulfstream
Glow Worm Ultramax
Ideal Istore
Potterton Powermax
..and so on...

Your mains must have enough pressure and flow. Test it. Fill a bucket and what is it in litres/min

* Fit a new larger bore mains water stoptap as these can restrict flow.
* A dedicated 22mm supply to the combi from the stoptap - no tee offs, except the cold to the showers which you take off just before the combi on the combi supply - any pressure variations around the combi will affect the shower too, to prevent serious pressure hot and cold pressure imbalances.
* All other cold supplies are teed of at the stop cock in their own dedicated line, which may be 15mm.

One approach is two combis
* can be side by side or stacked on the wall, say in the airing cupboard - taking up little space.
* One combi doing upstairs CH, one down (each with its own stat/programmer on the wall),
* One doing one bathroom, one the other. Divide and rule.
* Combine the outlets for baths to give 24 litres/min flowrate - the only outlet you need high flowrates.

Try the Atmos 12 litres/min Intercombi. Expensive but super reliable - no integral 3-way valve and the DHW works even if the pump fails.
http://www.tbsmerchants.co.uk/cgi-bin/build/detail/PA010010.html
Just under £800 each. So, £1,600 for two. Price up a quality RR boiler and a large megaflw and zon e valves, stat, et. A 250 litre Megaflow cyldiner is over £1,100 and 300 litres over £1,200, then around £1,000 for a quality system boiler. The Atmos combi route is hard to beat on price.

There is no need for a condensate pipe as they have a kit to squirt this out of the flue. This is more cost effective route than one boiler, zone valves, complex electrical controls and wiring doing the CH and an unvented cylinder. And you have CH and DHW backup if one is down. And you never run out of hot water and two people can have simultaneous showers and one not affect the other - for ever.

Now you can have upstairs off during the day saving money on bills - the system is naturally zoned by the combis, and showers at any time for as long as you want.

I personally would do the Atmos two combi route, after that a heat bank (thermal store cylinder)

Note: make sure on any mains pressure system that the showers mixer have integral pressure equalisation valves inside.

 

[lumi]

thanks for the replies - the concern really is that the water pressure isn't great so any combi boiler will have a low flow rate I guess. (?)

I notice you mention the ideal Istor. We thought that this was a new style system boiler that integrates the boiler and cylinder (is this right?). Would this then be a good system - a system boiler that acts like a combi and doesn't have tanks in the attic.

 

[Agile]

A supply pressure of 2.5 Bar is very good.

However the static pressure is virtually irrelevant.

Its the dynamic flow rate that matters. You need about 20 li/min @ 1 bar as a minimum to get good performance.

Tony

 

[gas4you]

The principle of an Istor is very good. I have not fitted any of these so cannot comment on the reliability.

Ideal boilers do have an unreliable name at present, but mainly on their Isar combis, so as this is based on the Icos one would hope it is more reliable.

 

[oakland99]

id go with gas4you, unvented with system boiler, i prefer megaflo (heatra sadia) unvented i find easy to repair and reliable...

 

[Doctor Drivel]

thanks for the replies - the concern really is that the water pressure isn't great so any combi boiler will have a low flow rate I guess. (?)

A large bore full-bore maintap improves flowrate, as does a dedicated 22mm pipe to the combi. How about a new main pipe back to the road? Once done it is done for life.

I notice you mention the ideal Istor. We thought that this was a new style system boiler that integrates the boiler and cylinder (is this right?). Would this then be a good system - a system boiler that acts like a combi and doesn't have tanks in the attic.

The Istor is as you say, a system boiler with an intergrated matched cylinder and optimised for efficiency. The floor mounted Viessmann, Vokera, W-B 440, Gledhill are thermal store heat banks inside, so can be DIYed. The others need G3 certification.

The wall mounted Vaillant 937 can be DIYed. The others need G3 certification.

As been said Ideal do not have good reputation for quality. Viessmann, ACV, Atmos are the RRs with W-B, Vaillant, Gledhill behind with Alpha now joining the 2nd tier after a dodgy period. The Gledhill can do 3 bathroom if the mains pipe is good enough.

All are on-box solutions. I would go for the ACV if it was me buying a floor mounted unit. A class act.

 

[Doctor Drivel]

id go with gas4you, unvented with system boiler, i prefer megaflo (heatra sadia) unvented i find easy to repair and reliable...

And an annual service for the customer just to have a cylinder of water standing still. AVOID!! Unvented cylinders are a last resort.

See my post on two Atmos combis vs a system boiler and unvented cylinder. Price wise, there is no contest.

 

[Agile]

Please ignore DD above.

He has a problem with CORGI registered people and those with the unvented qualification which most of us have if we are seriously involved with heating.

A pressurised HW store is the best way to provide HW to a property with more than one bathroom.

However, neither a combi or unvented will work unless the water supply is adequate.

That needs to be measured before making any decisions.

Tony

 

[oakland99]

id go with gas4you, unvented with system boiler, i prefer megaflo (heatra sadia) unvented i find easy to repair and reliable...

And an annual service for the customer just to have a cylinder of water standing still. AVOID!! Unvented cylinders are a last resort.

See my post on two Atmos combis vs a system boiler and unvented cylinder. Price wise, there is no contest.

see your post, was that the one that said get a pott powermax, yeah that would be great it will work for about a year then go wrong and no one will touch it just like the earlier powermax

 

[Doctor Drivel]

id go with gas4you, unvented with system boiler, i prefer megaflo (heatra sadia) unvented i find easy to repair and reliable...

And an annual service for the customer just to have a cylinder of water standing still. AVOID!! Unvented cylinders are a last resort.

See my post on two Atmos combis vs a system boiler and unvented cylinder. Price wise, there is no contest.

see your post, was that the one that said get a pott powermax, yeah that would be great it will work for about a year then go wrong and no one will touch it just like the earlier powermax

A year? Not my experience of them. Not the best but not like you say. Best use the maker men, not locals who don't know much at all. baxipot may like to comment.

I see you diverted the point to a Powermax, which was not under discussion at all on this thread. The point was two Atmos combis vs a system boiler/unvented cylinder. Think about it a lot.

 

[lumi]

we spoke to another plumber last night who has advised that we should put a 100-200gallon tank of water in our garage and pump it to a 42kw combi. He recons that should solve our problems as the water pressure coming in should then be sufficient to deal with the issue. Hopefully he is right....

Thanks for all your help.

 

[Doctor Drivel]

we spoke to another plumber last night who has advised that we should put a 100-200gallon tank of water in our garage and pump it to a 42kw combi. He recons that should solve our problems as the water pressure coming in should then be sufficient to deal with the issue. Hopefully he is right....

Thanks for all your help.

He had better put in suitable whole house pump with decent pressure lift - these are not cheap.

If you are going that route, then assess a mains water accumulator - a large pressure vessel holding mains pressure water. No pump needed as pressure is at mains static pressure. Still one of those in the garage in the garage attic space.

One can be made up quite easily and cheaply. I posted how to do it here once.

 

[Doctor Drivel]

Please ignore DD above.

The thermocouple changer is here again - the "service" man

A pressurised HW store is the best way to provide HW to a property with more than one bathroom.

True, but there are three ways of doing it:

1. Combi boiler
2. unvented cylinder (needs an annual service)
3. Heat bank (thermal store) No annual service.

No.2 is the worst choice

However, neither a combi or unvented will work unless the water supply is adequate.

That needs to be measured before making any decisions.

Which is rather stating the obvious.

Stick to thermocouples