Will a unvented cylinder work in conjunction with a combi?

[saltstein]

First of all I know very little about central heating, so please forgive me for my limited knowledge. I just know what I want to achieve.

I am having my detached house renovated (1 bathroom and 2 ensuites) and I do not want any lapse in water pressure when using showers and running baths etc. My builder advised that I should have a condensing boiler fitted alongside a unvented cylinder. So I bought a ferroli maxima 35c condensing combi and it has been installed. I have been told now by a plumber that really I should have had a system boiler to run the unvented cylinder. What I want to know is will a unvented cylinder work in conjunction with a condensing combi? I have not bought the cylinder as yet. Any advice would be helpful being as I have just paid out for a condensing combi.

Regards,

saltstein

 

[kevplumb]

What I want to know is will a unvented cylinder work in conjunction with a condensing combi? I have not bought the cylinder as yet. Any advice would be helpful being as I have just paid out for a condensing combi.

yes you need to pipe it on a s plan

 

[bster]

yes it will, just use the combi supplied hot water for the kitchen and a down stairs loo etc, the rest of the hot water supplys can come from the cylinder.

no prob what so ever, i've actually just read a section in my book (i'm an apprentice) that states that this combination of boiler and unvented cylinder is the ideal system for a multiple bathroom property.


you dont live in a 1 bed flat do you ?

 

[kevplumb]

last one i did was a 9 bed house jeeez you should have seen the bath

 

[bster]

kev you say S (as it is motor open spring return, ensuring that the cylinder wont overheat etc). So why do I have to do my unvented practical using a mid-position and 2 port safety valve, why bother with the mid position (DHW open at rest) Why would you install a mid and a 2port in the first place (unless its an addition to an existing y plan) and not 2 x 2 ports?

 

[Agile]

Wait a moment!

If you have an unvented cylinder then ALL your water usage in the house will be from the mains water.

Any competent engineer would have measured this before specifying anything!

Simply you need about 20 litres per minute to an open pipe for EACH bathroom as a minimum! Thats a massive 60 li/min total and unlikely to be available without upgrading the supply pipe ( about £1000 ).

Loft storage tanks and a VENTED cylinder are more likely to be achievable in the real world.

With such a demanding senario I think that you should be engaging somebody very experienced to specify your system otherwise you are likely to be disappointed.

Builders are businessmen and not heating engineers! Their motivation is to maximise their profits usually by getting you to spend as much as possible, not to fit whats best suited to your needs!

Tony Glazier

 

[ChrisR]

Why would you install a mid and a 2port in the first place (unless its an addition to an existing y plan) and not 2 x 2 ports?

You wouldn't, if you had half a brain. That seems to count a few plumbers out though. Spose I'll get some flak for that...

If you buy say a Megaflo you get a 2 port in the box, whicj you have to use, as it's part of the Approved set of parts making up the System..
It's the same as a standard 2 port, but that doesn't matter, you have to use the one they provide!
Part of the specified protection for a any UVHWSS is a normally-closed boiler-water isolating valve. The boiler-water could be at well over 100 degrees.

If you have to add a Megaflo (inc 2 port ) to a Y plan system, you have to do the wiring carefully!

MOD 2

calm down chris

 

[oilman]

I agree with Agile, but why did you fit a combi with it's unnecessary complexity? You say the builder suggested a boiler and cylinder, you don't mention he suggested a combi.

 

[saltstein]

First of all thanks for all your advice, so I guess broadly the answer is yes. The reason I am in this pickle is because the builder is doing loads of work in my house including the central heating. The deal was we would get a corgi registered plumber in (with unvented qualifications) to commission the boiler and install the unvented side of things. The builder has never dealt with unvented before, so does not know what pipe work needs to come off the boiler to accomodate the unvented system so that the plumber can go and fit the unvented side of things.

The builder figured by using a condensing combi boiler then like one of the posts says above the combi side of things can deal with the hot water for the kitchen and downstairs toilet and the hot water for the bathrooms can come from the unvented cylinder. What I am learning now is usually a system boiler is used in conjunction with a unvented cylinder and a combi adds a extra level of complication. However, I have already bought the boiler and it is installed so I am now forced to do things this way.

I don't want to be dissapointed with my setup so I have called a plumber for advice. However, although he has the unvented qualification he does not seem confident installing the unvented in conjunction with a combi. I guess I need to get in touch with a specialist who has experience fitting such a system. I live in Sheffield if anyone could recommend someone I would be really grateful. Regards, Saltstein

 

[saltstein]

Further to my message some months ago I have had my water supply upgraded and I am now ready to purchase a unvented cylinder for the central heating engineer to fit . I want a good quality efficient cylinder, I plan to stay in the property a long time. Based on the hot water outlets I have (stated below) a gentleman from range calculated that I would need a 300 litre tank. I would appreciate some advice on what make cylinder to go for? Depending on cost, I may be looking for a dual coil cylinder with solar in mind down the line in years to come. I have not asked the engineer because he is bias to one make.

4 showers
4 sinks
1 bath

kitchen hot water to be run direct from combi

I also have another query .. I read on a web site that you have to notify your local building inspector about adding a unvented system. Does anyone know is it just a case of notifying the building inspector or do you have to fill in forms and make a payment to the council?

Many Thanks in advance for your advice

Saltstein

 

[meldrew's_mate]

If you want a high grade cylinder try Megaflow or Santon Premier plus. I believe a solar option is available for the Megaflow.

I see from the postings you have already upgraded the cold mains - good: too low a dynamic pressure is the cause of many disappointments with unvented systems. Keep the large bore all the way to the cylinder with as few elbows as possible i.e not using the old (assumption!!) 15mm pipe.

Secondly, if you are using a commissioning fitter with the unvented qualifications they will be able to self-certify the installation, meaning no specific visit and cost from the Building Inspector, though make sure this is the case before they start (and check the qualies too!). The installer will have to register both the boiler and the cylinder through their registration body at a nominal cost to you (twenty quid or so), for which you will receive a certificate for your home information pack.

 

[gas4you]

Try the Vaillant Aurostor 300.

 

[saltstein]

Thanks for your help guys, the megaflow cylinder seems to be a popular one mentioned many times in this forum. I have a couple more further questions if you can help?

1) I know the difference between direct and indirect, but which one is the cheaper to run?

2) Is the megaflow cylinder direct or indirect?

3) Do you know of a cheap online supplier for the megaflow cylinder, preferably with the solar option?

Cheers,

Saltstein

 

[gas4you]

Indirect will usually be cheaper. For megaflo solar online look HERE

 

[defonarival]

I also have another query .. I read on a web site that you have to notify your local building inspector about adding a unvented system. Does anyone know is it just a case of notifying the building inspector or do you have to fill in forms and make a payment to the council?

Many Thanks in advance for your advice

Saltstein

If the unvented system falls within the G3 regulations then Building control require the installer to fill out and submit a self certification certificate upon completion. If the installer is not a member of any such scheme then building control shall inspect the installation and issue a certificate.......................for a fee of course.