Unvented Cylinder vs. Combi

Thanks to everyone who has taken the time to reply in this thread. There is lots of good information, perhaps also for anyone else is struggling with the same decisions.

The good news is that I already have a 22mm gas pipe between the gas meter and current boiler, therefore, not needing an upgrade if I change to a Combi.

The bad news is I cannot find the water route from the kitchen stopcock to the bathrooms. Worse still, there is a water meter beyond the stopcock, which has 15mm pipes, so upgrading the water feed to 22mm will need a new meter and significant investigation / removal of parts of the kitchen.

But, it seems the general consensus is, an unvented cylinder, with the annual checks and complications with pipe work is not the way to go.

@Bodd - I do need to measure the water pressure, although the pipe issue above will be an issue.

@sxturbo - My hot water flow rate is 6 ltrs/min from the kitchen tap and this is only tap connected directly to the cold mains is the kitchen tap (the outside tap is plumbed from the utility room). I remeasured the cold flow at the same time, and it was 12 ltrs/min.

I am intrigued by the pump solution. If I understand, these pumps (loft installed) have a pressure of around 5 bar (!!) and around 16 ltrs per min.

With a 250 ltr vented cylinder, assume a 50/50 mix of hot and cold, this gives around a 30 minute shower at some pressure!

It sounds like the best solution, considering the cost of two of these Aqualisa pumps is the same as the unvented cylinder.

Are there any downsides to putting pumps in the loft space, staying with a vented cylinder and heat only boiler (which I will need to replace at some point)?
 
Thanks to everyone who has taken the time to reply in this thread. There is lots of good information, perhaps also for anyone else is struggling with the same decisions.

The good news is that I already have a 22mm gas pipe between the gas meter and current boiler, therefore, not needing an upgrade if I change to a Combi.

The bad news is I cannot find the water route from the kitchen stopcock to the bathrooms. Worse still, there is a water meter beyond the stopcock, which has 15mm pipes, so upgrading the water feed to 22mm will need a new meter and significant investigation / removal of parts of the kitchen.

But, it seems the general consensus is, an unvented cylinder, with the annual checks and complications with pipe work is not the way to go.

@Bodd - I do need to measure the water pressure, although the pipe issue above will be an issue.

@sxturbo - My hot water flow rate is 6 ltrs/min from the kitchen tap and this is only tap connected directly to the cold mains is the kitchen tap (the outside tap is plumbed from the utility room). I remeasured the cold flow at the same time, and it was 12 ltrs/min.

I am intrigued by the pump solution. If I understand, these pumps (loft installed) have a pressure of around 5 bar (!!) and around 16 ltrs per min.

With a 250 ltr vented cylinder, assume a 50/50 mix of hot and cold, this gives around a 30 minute shower at some pressure!

It sounds like the best solution, considering the cost of two of these Aqualisa pumps is the same as the unvented cylinder.

Are there any downsides to putting pumps in the loft space, staying with a vented cylinder and heat only boiler (which I will need to replace at some point)?
 
Ash D said:
I am intrigued by the pump solution. If I understand, these pumps (loft installed) have a pressure of around 5 bar (!!) and around 16 ltrs per min.

With a 250 ltr vented cylinder, assume a 50/50 mix of hot and cold, this gives around a 30 minute shower at some pressure!
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You need to make sure that the Plumber follows the Manufacturers instructions when fitting pumps.
When exploring this option on jobs I priced It meant a new cylinder and new CWSTs. Then not so economic.

Look at Booster tanks if you have the room.Grundfos Spare/Slave Home Booster Water …Tank - 180Ltr This would work along side an Unvented cylinder.

Any good plumber can mke a bespoke system if a bigger capacity feeder tank is needed.
 
Tha bad news is, most of the information you have been given, is total Tosh by amature googlers who really havent a clue , get a pro in to quote for the works, you dont have to use them but al least they will have seen the site and can comment
 
ianmcd said:
Tha bad news is, most of the information you have been given, is total Tosh by amature googlers who really havent a clue , get a pro in to quote for the works, you dont have to use them but al least they will have seen the site and can comment
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Thanks Ian...:ROFLMAO:
 
ianmcd said:
Tha bad news is, most of the information you have been given, is total Tosh by amature googlers who really havent a clue , get a pro in to quote for the works, you dont have to use them but al least they will have seen the site and can comment
Click to expand...

Thanks Ian. I mentioned before, but I’ve struggled to get anyone to be remotely interested in this, hence, the plea for help on this site.

I’ve had multiple visits and quotes, all with differing views on the best installation solution, and then silence from all! Our 2 preferred people couldn’t even be bothered to return my calls and texts!

Considering that the total cost of the two bathrooms and boiler / cylinder could be many £thousands, I am really surprised at how little people are interested.

That said, The “new” plumber is super helpful, so I’m more hopeful that he will visit in the coming weeks.
 
Ash D said:
Thanks Ian. I mentioned before, but I’ve struggled to get anyone to be remotely interested in this, hence, the plea for help on this site.

I’ve had multiple visits and quotes, all with differing views on the best installation solution, and then silence from all! Our 2 preferred people couldn’t even be bothered to return my calls and texts!

Considering that the total cost of the two bathrooms and boiler / cylinder could be many £thousands, I am really surprised at how little people are interested.

That said, The “new” plumber is super helpful, so I’m more hopeful that he will visit in the coming weeks.
Click to expand...


Roughly what part of the country are you. You may get someone on here who's local to you.
 
Harry Bloomfield said:
No it is not. A great deal depends on the cold water mains flow and pressure.
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I have never seen a set up where you can't flush the toilet if the shower is in use. Not once, and I've seen a few over the years.
 
denso13 said:
I have never seen a set up where you can't flush the toilet if the shower is in use. Not once, and I've seen a few over the years.
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I have an electric shower. An electric shower demands much less water flow than a combi + shower, yet if anyone flushes either of the toilets the shower will shut off on low water pressure. If I use the bathroom toilet, intending to follow up with a shower, I have to wait until the cistern has refilled, before starting my shower.
 
denso13 said:
Seriously? So what if it takes a few seconds longer to fill, hardly life changing.
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As Harry has mentioned the pressure drop due to a cistern filling is enough to cause his electric shower to shut down.

Of course a combi boiler would never be affected in the same way would it ? Does the good book of boilers mention that as a possibility ?

If the good book doesn't mention it then it cannot happen. Even if it does happen the "engineer" who follows the good book will still say it cannot happen.
 
bernardgreen said:
Of course a combi boiler would never be affected in the same way would it ?
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I wouldn't say never but the combi bashers bring up these things, amongst others, all the time as if they are commonplace when they simply aren't.

A combi is, generally, pressurised to between 1 and 1.5 bar. If you have that pressure available do you really think flushing the toilet will stop the boiler working in some way?

If you don't have that pressure available then don't fit a combi as you won't be able to pressurise it in the first place.

I've said before, I have an old 28kw combi in a 5 bed house with two bathrooms and a WC and the combi is more than adequate.
 
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