Should I go Combi or Unvented?

[webbster]

I'm getting my loft done and ahead of that want to replace the boiler, which is an old NetaHeat. I have about 1.9 Flow rate according to a plumber mate who checked it. He says my options are as follows (I believe him but can't make my mind up as the wisest option)

MegaFlow - means paying about £1.5k extra for peace of mind of no leaks and reasonable pressure.

Combi - cheaper, less space needed etc, but the high pressure going through the CH increases the risk of hard to identify loss of pressure (ie leaks)

My reluctance re the Combi option is that when we moved in there was a leaky pipe in the hallway under the floor which was fixed (with plastic fittings). We've since laid a wooden floor (pinned and glued) so any hassle and cost of having to fix a leak might mean I should have gone unvented in the first place.

The house was built in 1778, and the CH system is easily as old as the outgoing boiler - probably a lot older.

Question is - are leaks that common with the combi route? Should I consider paying more now for peace of mind?

 

[middlesbrough]

They are bother sealed systems you can get a leak on either system .

I think unvented are the best systems especially for a family and especially for propertys with more than one bathroom ,

You might want to consider a twin coil cylinder if you go that route so its solar ready should you decide to add solar in the future (if not now)

Id say a unvented system is likely to require less maintenance than combis tend to over the yrs to come

 

[mysteryman]

I think you probably mean 19 litres per minute flowrate from your domestic water main. That being so, a combi will heat water at something near to that rate, so an unvented cylinder cannot achieve a better result.

Your cold main has to service all outlets at once - hot and cold.

 

[dcawkwell]

flow isnt important it can be compensated for the pressure both static and dynamic is more important

 

[oph]

Combis are crap.
Cheap for you short term but when you loose water AND heating in e future when it breaks down you'll wish you'd gone the unvented route

 

[mysteryman]

You can call it flow or dynamic pressure, or whatever you like. How much water can come from your main is what matters. There are plenty of people who like combis, just as there are plenty who don't.

All I was saying is that you won't get a better hot water delivery from an unvented cylinder if the water main cannot push enough water through it.

 

[JohnD]

how many baths and showers in your home, and how many taps are likely to be run at any one time?

have you got a big incoming water main that delivers a lot of water at good pressure? If you fill a bucket at the kitchen tap, and time it, how many litres per minute does it give?

 

[webbster]

So I just ran a bucket of water and got 8.5 litres from the cold tap in a minute.

I actually had a plumber round earlier this week and he said the only way you'd get an improvement on pressure is to replace the mains pipe out to the street.

And even then he felt the pressure wasn't good enough to warrant the expense of the unvented cylinder install. Another option though is to replace the mains pipe that at a later date if we weren't happy with the combi on its own.

So, I've decided to go for a Worcester Bosch 37 Combi - even though I don't really like Combis.

The driving factors are that I want to make space in the loft and in my daughter's room.

Now my only fear is whether there's sufficient oomph to be able to run a bath in the loft when we get that converted next month?

 

[lightning]

if you only got 8.5 litres a min no put having a 37 combi flow rate will be very poor, best with vented cylinder, and system boiler